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Reduced Interference In the Stroop Effect:
Determining When A Word 1s Read Automatically
Michael David Dodd
A thesis subrnitted in conformity with the requirements
for the degree of Master of Arts
Graduate Department of Psycholog
University of Toronto
G Copyright by Michael David Dodd (2001)
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Reduced Interference in the Stroop Effect:
Determining When a Word is Read Automatically
Michael D. Dodd
Master of Arts, 2000
Graduate Department of Psychology
University of Toronto
Besner, S tolz, and Boutillier ( 1 997) claimed to have eliminated S troop interference by colouring
only a single letter of an inelevant word and requinng participants to narne the colour of that
letter. On this basis, they argued that word reading could not be automatic. Four experiments
dernonstrated that their manipulation reduces but in lact does not eliminate Stroop interference.
It is argued that this reduction in Stroop interference is almost exactly offset by an equivalent
increase in latency due to the added requirement of searching For the coloured letter. This two-
process explanation adequately accounts for the Bcsner et al. ( 1997) results as well as oihrr more
recent results (Macleod, 1999; Mamurek, 1999). Moreover, i t is suggested that other aspects of
the Besner et al. methodolog may have produced the illusion that Stroop interference was
eliminated. Irrelevant words are read even in the single coloured letter variant of the Stroop task.
Acknowledgements
There are a nurnber of individuals who deserve special thanks for this, whether they are aware of it or not.
Fint, my wife, Jessica, for standing by me as I pursue my career goals. This path has been a long one and your love and patience through these times is mily appreciated. You are a large part of the reason 1 have been able to make it this far academically.
To ail of rny fnends who were always eager to listen to (or at least feign interest in) my rants whenever something was troubling me. academically or othenvise.
Thanks to Steve Joordens for providing me with insightful cornrnents and help whenever needed.
Most importantly, my supervisor and mentor, Colin MacLeod. You have provided me with geat insight and are always there when needed (even if only in spin t as you iravel the world looking for adventure a la Indiana Jones). Your hard work and investment into my work and rny future is greatly appreciated and will be remembered always.
Table of Contents
.............................................................................................................................. List of Tables vi .................................................................................................... List of Figures vil
... ................................................................................................................. Appendices Directory vrii
................................................................................................................................ Introduction 1 Reduction or Elimination of Semantic Prirning .................................................................. 5 Reducing or Eliminating the Stroop Effect: Colouring Only ri Single Letter ......................... S A Critique of the Besner, Stolz, and Boutilier ( 1997) Argument ............................................ 19 lnterpreting the Apparently Reduced Interference in the Single-Letter Coloured Condition ....... 27 Why the Reduction and Elimination of Sernantic Prirning May 'Iot Generalize to the Stroop
...................................................................................................................... E ffec t 1s Encoding the First Loner of an Incongruent Colour Word All That is Necessary to Invoke
............................................................................................ a Stroop Effect'? .+ln Extension of the Two-process account: CVill Letter Position Influence Response? .............. The Need for ri More Explicit Test of Whether Distractors are Read ..................................
............................................................................................. Negative Prirning'? Rationale for the Present Study ..............................................................................
................................................................................................... Gencral Method Apparatus and Materials ......................................................................................
...................................................................................................... Procedure Experirnent 1 ................................................................................................................................ 57
Method .......................................................................................................................... 57 ...................................................................................................... Participants 57
. . . . . . . . . . . . . . . . . . . . Procedure ................................ , 58 Results ........................................................................................................................... 58
Reduced Interference in the Single-letter-coloured Condition ........................ 58 ............................................................ Position of the Coloured Letter 61
Discussion .................................................................................................................... 64 Are Colour Nonwords a Suitable Control Condition'? ................................. 65
................................................................. More on PositionaI Effects 66 ................................................................... The Importance of Errors 67
..................................................................................................... Experiment 2a 69 ...................................................................................................................... Zilethod 72
Participants ..................................................................................................... 72
......................................................................................................... Procedure 73 ........................................................................................................ Results and Discussion 75
Colour 'laming Study Phase ....................... .. ..... .. ........................................ 75 .... .............................. Recognition Test Phase .... SZ
........................................................................ Recognition Latency 57 ............................................................................................................................... Experiment 2b 95
Method ........................................................................................................................ 97 ...................................................................................................... Participants 97
Materials ........................ ............. ........................................ 97 Procedure .......... .. ........................................................................................ 97
.............................................................................................. Discussion 102
................................................................................................................................. Expetitnent 3 1 03 ........................................................................................................................ Method 105
................................................................................ Participants ................. .. 105 .................................................................................. ................. Materials ... 105
....................................................................................................... Procedure 105 ..................................................................................................................... Results 106
............................................................................................... Discussion 106 ..................................................................................................................... General Discussion I l l
.................................................................................................... S m r y of the Findings 111 .................................................................. Where Does the Present Study Fit:' 114 .......................................................... Final Words on Besner et ai . ( 1997) ... ....... 11s
............................................................ Why Does Letter Position Not Matter? 122 .................................................. ............................. Suggestions for Future Research ... 125
........................................................................................ The Big Picture 118 .................................................................................................................................. Re ferences 131
List of Tables Page
Table 1: Mean Response Times (in ms) and Percentage Error Rates to Narne Colour as a Function of Condition (AI1 Letten Coloured vs. Single Letter Coloured). From Experiment 2: Besner, Stolz, and BoutiIier (1997). .................................................................... 12
Table 2: Mean Response Times (in ms) to Name Colour as a Function of Condition (Al1 Letters Coloured vs. Single Letter Coloured), Number of Display Colours (One vs. Two) and
.......... Cued Colour (Main vs. Odd) From Besner and Stolz (1999) Experiments 1 and 2.. 14
Table 3: .Mean Response Times (in ms) to Same Cotour as a Function of Number of Display Colours (One vs. Two) and Cued Colour (Main vs. Odd) in the Single Letter Coloured Condition From Besner and Stolz ( 1999) Experiments 3 and 4.. .................................. 16
Table 4: 'ulean Response Times (in ms) to 'iame Colour 3s a Function of Condition (Al1 Letters Coloured vs. Single Lctter Coloured) Xcross Four Groups (Vrirying Response Mode and Controls) From Marmurek (1999). ...................................................................... 23
Table 5 : .Mean Response Times (in rns) to Xame Colour as a Function of Condition (Al1 Letters Coloured vs. Single Letter Coloured) Across Four Groups (Varying Response Mode and Controls) From MacLeod ( 1999). ....................................................................... 26
Table 6: Mean Response Times (in ms) to Same Colow 3s a Function of Response .Mode (Vocal vs. Keypress vs. Typewitten) From Logan and Zbrodoff ( 1998). .................................. 35
Table 7: Mean Response Times (in ms) and Percentagr: Error Rates to Samc CoIour as a Function of Group ( 1, 2. or 3). From Bosner (2000).. .......................................................... 49
Table S: Experiment 1: Mean Response Times (in ms). Standard Deviations, and Error Rates to . Name Colour as a Function of Condition (Ail Letters Coioured vs. Single Letter Coloured).. 59
Table 9: Esperiment 1 : Mean Response Times (in rns). Standard Deviations and Errer Rates to Identify Colour as a Function of Letter Position (Incongruent CoIour Words vs. Control Items) in the Single Letter Colourcd Condition. ...................................................... 62
Table IO: Experiment 23: Mean Responsr Times (in rns), Standard Deviations, and Percentage Enor Rates to Xame Colour as a Function of Condition (.A11 Letters Coloured vs. Single Letter Coloured). .......................................................................................... 76
Table 1 1 : Experiment ?a: Mean Response Times (in ms). Standard Deviations. and Percentage Error Rates to Yame Colour as a Function of Lener Position in Single Letter Coloured Items at Study .............................................................................................. 77
Table 12: Experiment Za: Mean Recognition Rates and Standard Deviations for Hits (FulIy Coloured and Sinzle Letter Coioured Studied Words) and False A l a m ( Words Not Presented During the Stroop Task). .................................................................... 83
Table 13: Experiment Za: Mean Recognition Rates and Standard Deviations for CorrectIy Recognized Words (in the Single Letter Coloured Condition) as a Function of Coloured
.............................................................................................. Letter Position 84
TabIe 14: Experirnent Za: Mean Response Times and Standard Deviations for Words .Appearing During the Recognition Task as a Function of Response Type (Yes or Yo) and Word Type (Fully Coloured Single Letter Coloured, and 'lot Presented). ................................ 89
Table 15: Experirnenr 2a: Mean Response Times and Standard Deviations for Correctly Recognized .............. Words (in the Sinsle Letter CoIoured Condition) as a Function of Letter Position.. 90
Table 16: Experiment 2a: Mean Response Times and Standard Deviations (on the Recognition Task) Collapsed Across Conditions for Words That Xppeared During the Stroop Task
........ (Presented) and Words That Did Not Appear During The Stroop Task (Not Presented). 9 1
Table 17: Experiment 2a: Mean Response Times and Standard Deviations for Correctly .................... Recognized Words (Single Letter Colcwed) ris a Function of Letter Position. 93
Table 13: Experiment Zb: Mean Reading Times (in ms) and Standard Deviations ris a Function .................................. of Conditions (Al1 Letters Coloured vs. Single Letter Coloured). ,100
Table 19: Experiment 2b: Mean Reading Times (in ms) and Standard Deviations as a Function of ..................................................... Letter Position in Single Lener Coloured Words.. 101
Table 20: Experiment 3: Mean Reaction Times (in ms), Standard Deviations. and Error Rates to Name Colours as a Function of Condition (Al1 .Asterisks Coloured vs. Single Asterisk Coloured). .................................................................................................... 107
Table 2 l:_Experiment 3: Mean Reaction Times (in ms), Standard Deviations. and Error Rates to Name Colours ris 3 Function of Coloured .Asterisk Position in the Single Asterisk Colowed Position.. ......................................................................................... 1 OS
vii
List of Figures Page
Figure 1: Possible Patterns of Stroop Interference as a Function of the Position of a Single Coloured Letter (Assuming that the Stimulus Word is Six Letters Long.. .e.g., YELLOW). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendices Directory
Appendix A: Word Lists for Experiments 23 and 2b.. ................................................. Appendix B: Participant Consent Form.. .................................................................. Appendix B2: Participant Feedback Sheet.. ..............................................................
....................... Appendix C: Written On-Screen Instructions For Subjects In Experiment 1.. Appendix D: Written On-Screen Instructions For Subjects In Experirnent Za.. ..................... Appendix E: Written On-Screen Instructions For Experiment 2b.. ................................... Appendix F: W ritten On-Screen tnstmc tions For Experiment 3. . ..................................... Appendix G: Summary Table for a 2 x 2 Within Subjects AXOV.4 With Word Type (W)
and Colouring T,vpe (C) as the Independent Variables and Colour 'laming .................................................... Times as the Dependent Variable
Appendix H: Summary Table for a One Way tt'ithin Subjects ANOVA With Letter Position as the Independent Variable and Colour Narning Times as the Dependent Variable (For Control Words Only). ...................................
Appendix I I : Summary Table for a One Way Within Subjects AKOVA With Lener Position as the Independent Variable and Colour 'Jarning Times as the
..................... Dependent Variable (For Incongruent Colour Words Only). Appendix 12: Summriry Table for a 2 x 2 Within Subjects A.1:OV.A With Word Type (W)
and Colouring Type (C) as the Independent Variables and Error Rates as the Dependent Variable.. ...............................................................
Appendix J 1 : Summary Table for a One W3y Within Subjects XX0V.A With Letter Position ris the Independent Variable and Enor Rates as the Dependent Variable (For Incongruent Colour Words Onlyj.. ..................................
Appendix JZ: Summary Table for a One Wriy Within Subjects AXOV.4 With Letter Position as the Independent Variable and Error Rates ris the Drpendent
Variable (For Control iVords Only 1.. ................................................. Appendix J3: Summciry Table for a One Way Within Subjects .AXOVA With Word
Type as the Independent Variable and Error Rates as the Dependent Variable (For Distractors With the First Letter Coloured OnIy).. .................
Appendix 54: S u m r y Table for a One Way Within Subjects AXOVA With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Distractors With the Second Letter Coloured Only). ..............
Appendix J5: Summary Table for a One Way Within Subjects AXOVA With Word Type as the independent Variable and Error Rates as the Dependent Variable (For Distractors With the Third Letter Coloured Only). ................
Appendix J6: S u m r y Table for ri One Way Within Subjects ANOV.4 With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Words With the Fourth Lener Coloured Only). ....................
Appendix 57: Sumrn?ry Table for a One Way Within Subjects ;LC'OVA With Word Type as the independent Variable and Error Rates as the Dependent Variable (For Distractors With the Fifth Letter Coloured Only). .................
Appendix J8: Summary Table for a One Way Within Subjects ANOVA CVith Word Type as the independent Variable and Error Rates as the Dependent VariabIe (For Distractors With the Sixth Letter Coloured Only). .................
Appendix K 1: Sumrnary Table for a One Way Within Subjects ASOVA With Word Type as the Independent Variable and Colour 'laming Times as the
.......... Dependent VariabIe (For Words With the First Lener Coloured Only). Appendk KZ: Sunimary Table for a One Way Within Subjects hXOV.4 With Word
Type as the Independent Variable and Colour Naming Times as the ...... Dependent Variable ( For Words W ith the Second Letter Coloured Only).
A p p e n d ~ ~ K3: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent VariabIe and Colour Saming Times as the Dependent Variable (For iVords With the Third Letter Coloured Only). .........
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Appendix K4: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Naming Times as the
......... Dependent Variable (For Words With the Fourth Letter Coloured Only). 159 Appendix KS: Summary Table for a One Way Within Subjects ANOVA With Word
Type as the Independent Variable and Colour Naming Times as the .......... Dependent Variable (For Words With the Fifth Letter Coloured Only). 160
Appendix K6: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Naming Times as the
......... Dependent Variable (For Words With the S~xth Letter Coloured Only). 16 1 Appendix L: Summary Table for a One Way Within Subjects ANOVA With Colowing
Type (All Letters or One Letter) as the Independent Variable and Colour ........................................... Naming Times as the Dependent Variable.. I62
Appendix .M: S m r y Table for a One Way Within Subjects ASOVA With Letter Position as the Independent Variable and Colour Naming Times as the Dependent Variable.. .................................................................... 163
Appendix N: Summrtv Table for a One Way Within Subjects ANOVA With Colouring Type as the Independent Variable and Error Rates as the Dependent Variable. ................................................................................. 164
Appendix 0: Surnmry Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Error Rates as the Dependent Variable ...................................................................................... 165
Appendix P: S u m r y Table for a One Way Within Subjects AXOVA With Word Type (Full): Coloured vs. Single-Letter-Coloured vs. Xot Presented) as the
....... Independent Variable and Recognition Rates as the Dependent Variable.. 166 Appendix Q: Summary Table for a One Way Within Subjects ANOVA With Letter
Position as the Independent Variable and Recognition Rates as the Dependent Variable.. ...................................................................... 167
Appendix Rl: Summary Table for a One Way Within Subjects ASOVA With Response Type (Fully Coloured Hits vs. Single-Letter-Coloured Hits vs. Unstudied
False Alarms) as the Independent Variable and Recognition Response Times .............................................................. as the Dependent Variable.. 168
Appendix RZ: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Recognition Response Times
................................................................ as the Dependent Variable 169 Appendix S: Summary Table for a One Way Within Subjects ANOV.4 With Letter
Position as the Independent Variable and Recognition Response Times as .................................................................. the Dependent Variable.. 170
Appendix T: Summary Table for a One Way Within Subjects ANOVA With Colouring T>pc as the Independent Variable and Word Reading Times as the Dependent Vanable.. ....................................................................... 17 1
Appendix L': S u m r y Table for a One Way Within Subjects ASOV.4 With Letter Position as the Independent Variable and Word Reading Times as the Dependent Variable.. ....................................................................... 172
Appendix V1: Summslry Table for a One Way Within Subjects ASOVA With Colouring Type as the Independent Variable and Colour Naming Times as
...................................... the Dependent Variable (For Rows of Asterisks). 173 Appendix VZ: S m r y Table for a One Way Within Subjects XXOVA With Letter
Position as the independent Variable and Colour Naming Times as the ............................................ Dependent Variable (For Rows of .4sterisks) 174
Appendix W 1 : Summary Table for a One Way Within Subjects ANOVA With Colouring Type as the Independent Variable and Error Rates as the Dependent Variable (For Rows of Asterisks). ........................................................ 175
Appendix W2: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the independent Variable and Error Rates as the Dependent Variable (For Rows of Asterisks). ....................................................... -176
Reduced Stroop Interference - 1
Since the influentid writings of Cattell(1886). psychological literature has routinely
distinguished between controlled and automatic processes. Any new task is assumed to be
controlled in that. at the outset, it requires a geat deal of attentional resources to perform.
Gradually, however, as an individual becomes more practiced at the task, the resources required
to carry it out decrease. This process was descnbed very well by Schneider. Dumais. and
At first, effort and attention must be devoted to each movement or minor decision, and performance is slow and error prone. Eventually, long sequences of movements or cognitive acts are camed out with Iittle attention, and performance is quite rapid and accurate .... The striking changes that occur with practice have Ied many researchers to propose that qualitative changes
occur in the processing. (P. 1)
As an example, consider an individual first Iearning to drive a car. Initially. a great deal of
attention is paid to the pedals, the gear shifl, mirrors, blindspots, speed, etc. As an individual
gains more driving expenence. however. these things that were initially given a great deal of
attention are now perfonned with great ease and little effort on the pan of the driver. Whereas
the beginning driver has to direct a good deal of attention toward dnving the car, the skilled
driver navigates virtually effortlessly and has resources remaining to engage in other activities
simultaneously if they so wish (e.g., conversing, changing radio stations or, in my fat her's case,
reading) .
It is important to realize that although driving becomes a fairly automatic task. it never
becomes 100% automatic. Attention still must be paid to trafic lights. signs, and directions.
Such is the case with many automatic tasks: Despite the reduction in effort and resources that
cornes with practice, it is still necessary to have control over cenain aspects of every task.
Although the manner in which you drive to work every day may seem "automatic," you would
Reduced Stroop Interference - 2
not want to drive to work automatically on the weekend when your destination was actually the
mall. Thus, the concept of automaticity does not imply that al1 aspects of a task are always
camed out without any effort; it simply suggeas that with practice, less control is required to
perform many tasks.
Friedrich. Henik, and Tzelgov (199 1) outline three main characteristics that constitute
automaticity. First. an automatic process is "effortless in the sense that it does not require the use
of a limited-capacity attentional system" (p. 792). It should be noted, however, that although
such a process requires relatively few resources. it is not always possible to perform numerous
"automatic" processes sirnultaneously. Second. automatic processes develop fiorn increased
practice of these processes. Third, once an automatic process has been activated. it is very
difficult to prevent. This latter point is illustrated nicely by the Stroop effect. often regarded as
the Rosetta stone for automaticity in word reading (Posner & Snyder, 1975).
The Stroop effect was developed by Stroop in 1935, though he was not so pretentious that he
narned it afler himself at the time (MacLeod. 1991). Stroop's discovery was that if an individual
was asked to read a list of colour words when each word was pnnted in a mismatched ink colour
(e.g.. RED in green, Say "red), they would be able to cornplete this task quite easily. If,
however. the task was to name the ink colour rather than the colour word (e.g.. RED in green.
Say "green"), performance was considerably slowed, despite explicit instructions not to read the
word. Thus, the word is thought to be read automatically and consequently the individual c m o t
avoid this interference. Indeed, the Stroop effect has often been considered a key piece of
evidence for the idea of automaticity in reading words (e.g., Posner & Snyder, 1975).
The Stroop effect. however, is just one of many exarnples of automatic processing. Another
often cited automatic effect involves sernantic priming in word pairs. The sernantic priming
Reduced Stroop Interference - 3
effect refers to the phenomenon whereby the processing of a word is facilitated when preceded
by a semantically related context (Neely, 1977). As an example, the word "nurse" is responded
to more quickly in a lexical decision task, where the task is to decide if a string of letters foms a
word. when preceded by the word "doctor" as opposed to the word "bicycle."
Friedrich et al. (1991) built on the work of Neely (1977) and Posner and Snyder (1975), and
pointed to three processes which they assumed to be integral for semantic priming: automatic.
attentional, and postlexical. The automatic process is related to a rapid spread of activation in
memory from the stimulus or concept that is activated to a11 related stimuli or concepts, which
are quickly primed. As an exampie. if an individual were presented with the letter "a," it is
thought that "the lexical representation of a11 words containing that letter will also receive sorne
degree of activation" (Friedrich et al., 199 1. p. 792). Thus. they consider human memory to be a
network of interconnected representations. be they visual. semantic. or phonological. The
representations are thought to be interrelated so that the activation of a visual cue may also
activate a corresponding semantic or phonological cue (cf. Seidenberg & McClelland. 1989).
This activation is not under the control of the individual. Simple presentation of a stimulus
"automatically" activates related concepts at some level (Friedrich et al.. 1 99 1 ).
The second aspect of semantic pnming involves attentional processes. The attentional
mechanism is thought to generate a series of words andor concepts that are related to the prime
word that has been presented (Friedrich et al., 199 1). As an example, if the word "doctor" was
presented to an individual as a prime, the individual would then generate a list of words that
could follow, ranging fiom highly likely (e.g., nune) to less likely (e.g., stethoscope). The idea
of "likelihood of response" is what sets apart attentional processes from automatic processes.
Whereas automatic processes spread through mernory activating a11 related concepts. attentional
Reduced Stroop Interference - 4
processes are more selective, priming some words more than others. In the previous example.
the word "nurse" would be more highly pnmed by the word "doctor" than by the word
"stethoscope." Friedrich et al. (1991) refer to this as the relatedness proportion effect.
Fnednch et al. (199 1) also speak of a third priming mechanism in semantic prirning, a
mechanism which occurs at the postlexical level. The authors provide this example of a
semantic-matching process:
... after lexical access of the target word has occurred, the presence of a relationship between the prime and target words can be used to speed the word-nonword decision process. (Friedrich et al., 199 1, p. 793)
Collectively, these three processes are thouçht to combine to create semantic priming. Semantic
priming effects are found under a variety of situations ranging fiom verbalizing the prime word
(e.g.. Henik et al.. 1983) to making semantic judgments about a prime (e-g.. Parkin. 1979: for an
extensive Iist, see Friednch et al.. 199 1).
Aithough both the Stroop effect and the semantic priming effect are key examples of
automaticity, there is an interesting finding that separates these two effects: A nimber of studies
that have documented procedures that can eliminate the semantic priming effect by changing the
manner in which the participant orients to the prime (e.g., Henik et al.. 1983; Smith. Theodor. &
Franklin, 1983). Despiie a number of documented ways to reduce Stroop interference (e.g.,
manual response; see MacLeod, 199 1. for a review). no methodology had yet led to an
elirnination of the Stroop effect. That was until 1997 when Besner, Stolz, and Boutillier claimed
that they had elirninated Stroop interference by colouring only a single letter of an irrelevant
word and requiring participants to name the colour of that letter. Their interpretation of their
results has come under scrutiny from a number of researchers (e.g. Marmurek. 1999; MacLeod.
1999), as have several aspects of their methodology.
Reduced Stroop Interference - 5
This thesis will explore the concept of automaticity in the context of the Stroop effect and the
elirnination of semantic priming. It was the reduction and elimination of oemantic priming in
past studies that led Besner et al. (1997) to determine whether they could eliminate the Stroop
effect by a sirnilar manipulation. The original Besner et al. (1997) study and its successors will
be reviewed as will the unpublished work by Mamurek (1999) and MacLeod (1999) which
question the Besner et al. ( 1997) methodologies and conclusions. Altemate explanations and
interpretations for the results of these studies will be presented. Finally. new research will be
laid out as an attempt to add further insight to the processes that could account for Besner et al.3
( 1997) results
Reduction or Elimination of Semantic Priming
Numerous studies have been conducted which have shown that the effects of semantic
priming can be altered (e.g.. reduced or eliminated) if certain procedural modifications are made.
Most notably. researchers have been able to elirninate priming effects by changing the manner in
which the panicipant orients to the prime (e.ç., Henik, Friedrich. & Kellogg, 1983; Smith.
Theodor. & Franklin. 1983). Henik et al. (1983) had participants perform one of two tasks on a
prime (naming or letter search) and one of two tasks on a target (lexical decision or colour
naming). Interestingly. when the prime was named. lexical decision was facilitated whereas
colour naming was impeded. Both of these effects were eliminated. however. when a letter
search task was performed on the prime.
Other researchers have employed procedural modifications such as varying the stimulus onset
asychrony (e-g., Besner & Stolz, 1996: Neely, 1977) or having participants scan letters of a target
rather rhan responding to that target as a word (e.g.. Henik. Friedrich, & Kellogg, 1983). One of
the best examples of this latter approach is the study conducted by Friedrich et al. (199 1) to
Reduced Stroop Interference - 6
examine the influence of semantic primes presented in the context of a letter search task. Similar
to Henik et al. (1983). these researchers compared differences in semantic priming magnitude
when participants were asked to name a prime word as opposed to searching through that prime
word for a target letter. The idea was to determine whether semantic primes would still be
encoded at a lexical level when searching for a target letter. even though this was not necessary
for the task. To investigate this. they presented participants with three different types of primes:
Semantic. cross-case identity. and unrelated. Identity priming is essentially repetition prirning,
with the prime word also being presented as the target word. Cross-case identity priming refers
to repetition priming in which the prime appears in lowercase letters whereas the target appears
in uppercase letters (or vice versa). This method of presentation ensures that priming is due to
the word itself rather than just to a lingenng iconic representation of the features or shape of the
word. When participants were asked instead to search for a probe letter in the prime. semantic
priming was eliminated. Identity priming remained, however. thus supporting the idea that the
lexical propenies of the prime word are encoded even in the letter search task. which apparently
only prevents the individual from making semantic associations.
The results of two subsequent experiments by Friedrich et al. (1991) indicated that lexical
priming was undected by switching to the letter search task. Thus, even when a word is
scanned letter by letter, the participant detemiines a lexical identity for the word that then primes
the word in identity pnming. This is an important finding as it demonstrates that letter by letter
processing does not necessarily lead to a disruption in word reading. Consequently, identity
priming was attributed to lexical priming rather than to letter by letter priming. A founh
expenrnent indicated that semantic priming retumed if the word was also spoken aloud by the
expenmenter, even when the participant was instructed to scan for target letters.
Reduced Stroop Interference - 7
Previous studies had demonstrated that responding to a prime word in a nonlexical marner
reduced or eliminated the facilitation from semantic associates (e.g., Henik et al., 1983). The
Friedrich et al. (1 99 1) study demonstrated differential effects of priming for identity vs. semantic
targets when participants were required to visually scan the prime word for a probe letter. The
reduction of semantic priming did not seem attributable to nonlexical priming. Indeed, it appears
as though a lexical entry for prime words is encoded. even when the prime word is s c a ~ e d for a
probe letter. "These data instead suggest that either activation of semantic features of the prime
word or activation of semantic associates is disnipted" (Friedrich et al., 199 1. p. 802). Semantic
priming was reinstated. however, when that prime word was auditorily presented to the
participant. even when the prime word was being scanned for a probe Ietter. Presumably, this
occurs because searching a word for a probe letter may make the word easier to ignore. or less
wordlike because it is broken down into its individual letter components. Presenting the word
uiidiroriiy makes it more difficult to ignore. however. even if the individual has visiially parsed
the word into individual letter cornponents (it would be an interesting but difficult task to try and
attempt to have participants break down words into their individual sound components. and
determine whether this would also reduce semantic priming by making the word less wordlike).
Thus, it appears as though simply presenting a prime is not sufficient for priming effects to
occur. Rather. the individual must process the prime word in a certain way to a certain level.
Henik et ai. (1983) offer an intriguing explanation for these effects, saying that:
... activation of semantic associates rnay require some attentional resources and that the letter-search task focuses resources at the Ietter level, thus preventing spreading activation to related concepts.
(Friedrich et al., 199 1. pp. 793-794)
.Athough the prime word may be processed at some level, that processing may not be enough to
Reduced Stroop Interference - 8
activate related concepts. Friedrich et al. (1 99 1) oEer a different explanation. When the
semantic prime is broken down into letter components by having participants search for a target
letter, prime words may not be encoded lexically, eliminating the beneficial effect of the prime.
This point is important as it provided the grounds on which Besner et al. (1997) posited that they
could eliminate Stroop interference by colouring a single letter of an irrelevant word.
Similar findings to those of Friedrich et al. ( 199 1 ) have ansen from the direct and indirect
remembering literature. It appears as though simply presenting a word to an individual is not
suficient for that word to be consciously remembered (MacDonald & MacLeod, 1998). Some
level of attentional resources is necessary for a word to be encoded. coinciding with the Friedrich
et al. (199 1) suggestion that there may be a partial attentional component to automatic processes.
If these attentional resources are disrupted, then the normal priming effects associated with
presenting words may be reduced or eliminated. Results from these and similar studies have
been used to cal1 into question the "automatic" word processing that was assumed to be present
in semantic priming.
Reducing or Eliminating the Stroop Effect: Colouring Only a Single Letter
The purpose of the present thesis is to investigate the possibility that the Stroop effect can be
eliminated in like manner, a claim made by Besner et al. (1997). Stroop interference on a single
incongruent item has been demonstrated to be as large as 180 ms (MacLeod. 199 1). Besner et al.
(1997), however, claim that the results of their second experiment show that the Stroop effect
can be completely eiiminated by colouring only a single letter rather than the entire word.
Besner et al. (1997) were cunous to determine whether the reduction and perhaps elimination
of semantic priming effects in the lexical decision task would generalize to a reduction or
elimination of semantic priming effects in the Stroop task. To investigate this, they performed
Reduced Stroop Interference - 9
two experiments. They predicted that if only one letter of a word were coloured in a Stroop task,
this mi@ negatively affect the processing of the word as a word and consequently reduce andor
eliminate the S troop effect. The logic of this research is thus sirnilar in nature to the studies of
Friedrich et al. (1991) and others with regard to semantic priming. Although the Besner et al.
(1997) study contained two experiments, it is the second of these that is most relevant to the
present proposa1 and as such will receive the most attention. This is not to Say. however. that the
first experiment is not important, as it has helped to lay the theoretical groundwork for the
present t hesis.
In their first experiment, Besner et al. (1997) used a colour word condition (e.g.. BLUE in
red) and a pseudohomophone condition (e.g., BLOO in red) "to assess the idea that the Stroop
effect is nonnally larger for words than for the pseudohomophones" (p. 222). Stimuli appeared
in either a congruent colour (e-g., RED in red) or an incongment colour (e.g., RED in green) with
either the entire word coloured or a single letter of varying position coloured. Sixty-four
participants each perfonned 288 test trials and 72 practice trials in which al1 eight conditions
(Le., word type X congmency condition X amount coloured) were intermixed. balanced. and
randomly presented. Participants were to indicate the colour of the entire word or of the single
coloured letter by pressing one of four buttons on the keyboard corresponding to the four colours
used (red, yellow. green. and blue).
Analyses indicated that congruent trials were responded to faster than incongment trials. This
finding is consistent with a great deal of past research on the Stroop effect (MacLeod, 199 1). As
well. fully coloured words were responded to more quickly than words containing a single
coloured letter. There was no effect of word type (colour word vs. pseudohomophone). but there
were two significant interactions. First, there was an interaction between the congniency
Reduced Stroop Interference - 10
condition and the word type, with a larger Stroop effect occurring for colour words relative to
pseudohomophones. This would be expected on the basis of many studies investigating the
impact of word type (e-g., Klein, 1964). Most critically, though, there was also an interaction
between the congruency condition and the method of colouring, with larger interference
occurring for fully coloured words relative to single-letter coloured words. Besner et al. (1997)
took these results to suggest that the notion that words are read automatically may be too strong:
If words are always read autornatically, there should not be a difference in the magnitude of the
Stroop effect for fûlly coloured words vs, words with only a single letter coloured. It is worth
noting that a similar argument was made against strong automaticity and in favour of weak
automaticity by Kahneman and Chajczyk (1983) in their "Stroop dilution" studies. Besner et al.
(1997) also argued that the reduced Stroop effect for pseudohomophones relative to words is
evidence that there is more to semantic comprehension than simply phonemics. Theii second
experirnent extended this argument.
Experiment 2 was similar in procedure but featured two key differences: Congruent t d s
were eiiminated (because they encourage the participant to read the word) and
pseudohomophones were replaced with a control condition referred to as "congnient nonwords"
( E T . YENILE. GREM), and BLAT). The use of the word "congnient" applied to nonwords
serving as controls in the context of Stroop research is somewhat confusing, so it may be better
to refer to their controls as "colour nonwords." Besner et al. (1997) chose these control items
rather than baseline X's because, to thern, these items appeared more word-like. Also, the
"controls were chosen to match the incongruent stimuli on Iength and on the first two letters.
given the repeated worry that a Stroop effect cm result simply from the first two letters spelling
a color word" (p. 223). This is an intriguing argument, and one :hat will be examined in more
Reduced Stroop Interference - 1 1
depth &er their Experiment 2 has been reviewed.
In Experiment 2. 64 participants perfonned 36 practice trials followed by 144 experimental
trials. The response tirnes and error rates are presented in Table 1. Again, single letter coloured
stimuli took longer to respond to than did M y coloured words. AIso, incongruent triais took an
overall longer time to respond to than control trials. Finally, there was a critical interaction
between the congruency condition and colouring type. with no Stroop interference apparent
when a single letter was coloured relative to the entire word. It is this last finding that provides
evidence that the Stroop effect has been eliminated. In their words "simply coloring a single
letter instead of the whole word eliminated the Stroop effect" (Besner et al.. 1997. p. 22 1). As
Table 1 shows. when only a single letter appeared in colour, there was no difference between
incongment and control condition response times relative to a 30 ms difference when words
appeared fully coloured. Besner et al. (1997) clairned that these results were proof that the
Stroop effect could be elirninated and that. therefore. automaticity accounts of word reading are
too strong.
This line of work has continued in a series of subsequent articles. Besner and Stolz ( 1999a)
hypothesized that the elimination of the Stroop effect in their 1997 study could have been due to
a narrowing of spatial attention that prevented lexical activation of target words. Thus. they
designed four expenments to test the level of Stroop interference under a variety of different
spatial and colour conditions. In their first two expenments. they used the incongment and
congruent conditions (e.g., colour words appeanng in either congruent or incongment colours).
There were two experimental manipulations. The first was a cuing manipulation that consisted
of a single arrow or string of arrows appearing above and below either the entire colour word, a
single coloured letter which displayed the colour to be named. or a single coloured letter which
Reduced Stroop Interference - 12
Table 1
Mean Response Times (in ms) and Percentage Enor Rates to Name Colour 'as
3 Function of Condition (Al1 Letters Coloured vs. Single Letter Coloured). Froin
Emerirnent 2: Besner. Stolz, and Boutilier ( 1997).
NI Letters Colored Single Letter Coloured
Incongnient 777 2.9
Control 713 2.4
Difference 34 0.5
Note: RS = response Times; %E = percentage of errors
Reduced Stroop Interference - 13
displayed a colour other than that which was to be named. The second was a colour
manipulation in which colour words appeared entirely in one colour (e.g. RED in blue) or in two
colours with one letter in the colour to be named and the other letters in one of the other three
colours used (e.g., RED with R in green and ED in yellow). The only difference between
Experiments 1 and 2 was that colour words in Experiment 2 were displayed with a blank
character space between successive letters "to investigate whether larger spaces between adjacent
letters would lead to irnproved spatial selection" (p. 100). In all, there were 256 trials that
consisted of 8 blocks of 32 trials for each experimental manipulation. As in the Besner et al.
(1997) snidy, al1 responses were made manually.
The results of the first two experiments are presented in Table 2. The key finding was that
cuing a single letter when only one consistent display colour was used reduced Stroop
interference relative to cuing al1 letters. When al1 letters were cued, 126 ms of interference was
observed whereas only 88 ms of interference was observed when a single letter was coloured.
When two colours were used on each Stroop display. the results indicated that cuing the to-be-
responded-to congruent colour decreased interference relative to cuing the dominant incongruent
display colour. When the dominant incongruent display colour was cued, 33 ms of interference
was observed whereas ody 2 1 ms of interference was observed when the to-be-responded-to
congruent colour was cued. The pattem of results in Experiment 2 was comparable to that of
Experiment 1. with the sole exception that responses were made more quickly in every condition.
The pattem of interference, however, did not seem to be significantly reduced by displaying a
blank character space between successive letters. Although the manipulations in the first two
experiments led to a reduction in interference, the researchers were certain that this interference
could be eliminated, so they designed two further experiments to test this notion.
In Experiments 3 and 4. both single colour displays and congrnent trials were elirninated. In
Reduced Stroop Interference - 14
Table 2
Mcan Remonse Times (in ms) to Name Colour as a Function of Condition (Al1 Letters
Coloured vs. Single Letter Coloured). Number of DimIav Coloun (One vs. Two) and
Cued Colour (Main vs. Oddl From Besner and Stolz (1999) Esmriments 1 and 2.
All Letters Colored Single Lctter Coloured
Colour Condition Incongrucnt Conruent Difference Incongnicnt Congruent Diffcrcncc
One Colour 897 77 1 126 866 788 78
Two Coloun %tain Colour Cued N/A N/ A N/A 952 9 19 3 3 Odd Colour Cued NIA NIA NIA 905 884 2 1
One CoIour 860 73 2 128 8 13 75 1 62
Two Colours Main Colour Cued N/A N/ A N/ A 880 829 5 1 Odd Colour Cued N/ A NIA N/ A 830 805 2 5
Reduced Stroop Interference - 15
place of congruent triais, the researchers used the colour nonwords from Besner et al. (1997) as a
control condition "to elirninate any benefit from reading the word" (p. 102). Due to the
elimination of single letter coloured trials, the cue manipulation now consisted of oniy single-
letter cues, rather than whole-word cues. The only difference between Experiments 3 and 4 was
that the to-be-responded-to colour was cued on half of the trials (the incorrect colour was cued
on the other half of the trials) in Experiment 3 whereas the to-be-responded-to colour was cued
on every trial in Experirnent 4. Thus, Experiment 4 encouraged "spatial selectivity" as the
desired response was always precued whereas attending to the cued position in Expenment 3 was
not necessarily helpful. and in fact, potentially hindenng (on 50 % of the triais).
The results of Experiments 3 and 4 are presented in Table 3 . These expenments provided
further evidence that the Stroop effect could be eliminated. When the dominant colour (not the
to-be-responded-to colour) was cued in Experiment 3. there was still 18 ms of interference based
on the difference between incongruent trials and neutral trials; however. when the to-be-
responded-to colour was cued, this difference was reduced to 1 ms. Similarly, in Experiment 4.
there was a small but nonsignificant difference of 9 rns between incongment and neutral trials.
These findings are in accord with Besner et al. (1997) and consequently. were interpreted by
Besner and Stolz (1999a) as further evidence that Stroop interference can be eliminated. and that
therefore word reading is not automatic.
In a further study. Besner and Stolz (1999b) investigated the relation between spatial attention
and the Stroop effect by rnanipulating the position of a coloured letter in colour words, shape
words. and geometric objects. In their first two expenrnents, either colour words (red. blue.
green, yellow), colour-neutral words (these words were al1 five Ietters in length but no
description was explicitly given). or shape words (circle, triangle, square) appeared within a
Reduced Stroop Interference - 16
Table 3
Mean Response Times (in ms) to Name Colour as a Function of Nurnber of DimIav
CoIours (One vs. Two) and Cued Colour (Main vs. Odd) in the Single Letter Coloured
Condition Frorn Besner and Stolz (1909) Eswriments 3 and 4.
Colour Condition Incongrnent Congrnent Difference
Expcriment 3
Two Colours
Main Colour Cued
Odd Colour Cued
Eweriment 4
Two Colours
Odd Cotour Cued 820
Reduced Stroop Interference - 17
bounding box. These words appeared with either a single letter coloured or with every letter
coloured. When a single letter was coloured. its position was randomly determined. Unlike the
previous studies, however. the coloured letter could not appear in every position: Only the
beginning (first), middle (third), and end (fifth) positions were used. The display colour to be
responded to was either congruent or incongruent with respect to the colour words. In the third
experiment, distractor colour words appeared within geometric shapes (circle. triangle. square)
whose borders were either fully coloured or partially coloured. As with the two previous studies.
participants responded manually to the colour display.
The results of these experiments again indicated that Stroop interference was a fbnction of
spatial attention. When targets appeared fully coloured, there was approximately 33 ms of
Stroop interference based on the difference between incongruent and congruent trials in every
experiment. When only a single element of a target was coloured. however. interference was
eliminated in both Experiments 1 and 2. This effect was most pronounced in the second
experiment using shape words. In Experiment 3. however. colouring a single element still
resulted in 20 ms of interference. Besner and Stolz (1999b) provided the following interpretation
of their results:
When the color camer stimulus and the spatially distinct color word belonged to the same domain (Le., when they were both words), the single-colored-element manipulation largely eliminated the Stroop effect (Expenments 1-2). Ln contrast. when the color camer stimulus and the spatially distinct color word belonged to difFerent domains. the single-colored-element manipulation produced a Stroop effect that was as large as when the color camer stimulus was al1 colored.
(P. 453)
Collectively, Besner et al. (1997; Besner & Stolz 1999ah) concluded that the Stroop effect can
be eliminated when participants are made to perform a letter search task on distractor words.
Reduced Stroop Interference - 18
They concluded that this was caused by blocking the flow of activation to semantics:
Explicit processing of a letter's form or color in the context of a word is associated with letter and lexical level activation that is blocked from flowing strongly to the semantic level. Instead, lexical level activation feeds back to the letter level to enhance processing there.
(Besner et al.. 1997, p. 224)
Besner et al. (1997) offer little additional suppon for this argument. For this idea to be
plausible. one would have to provide direct evidence that letter search tasks divert attention From
semantics while simultaneously enhancing letter-level processing. In fact. evidence to the
contrary was presented in an earlier study by Besner himself. Besner. Smith. and MacLeod
(1990) investigated the effects of semantic relatedness when pairs of related words. unrelated
words. or nonwords were searched for a common letter and found that "even though participants
were set to look for individual letters in the search task. semantic level processing occurred" (p.
866). Indeed. words that were semantically related were processed more slowly than words that
were semantically unrelated in a letter search condition even though semantically related words
pairs were processed much more quickly than unrelated pairs in a lexical decision task.
Stolz and Besner (1996) also demonstrated semantic priming effects in a letter search task
when there was a short stimulus onset asychrony between the prime trial and the probe trial.
Thus. switching to a letter search paradigm did not prevent a flow of activation to the semantic
Ievel in either of these studies, though it did result in differential effects of semantic relatedness.
This point will again be important when we consider the work of Besner et al. (1997) who
argued that colouring a single letter of a word prevents activation of that word at the semantic
level and as a consequence. eliminates Stroop interference. Their explanation for this
elimination of the Stroop effect was the same one that they had previously offered to explain the
elimination of semantic priming when a letter search task is used. Their explanation relies on the
Reduced Stroop Interference - 19
concept of "blocking" which they use to identie the prevention of a normally well established
automatic process (word reading) due to an increased focus on the nonlexical aspects of an
irrelevant word (in this case. the coloured letter). Besner et al. (1997) argue that. in essence,
colouring a single letter directs attention towards individual letters, thereby, preventing the
irrelevant word From being viewed as a whote. This argument is dependent upoo the observed
equivalence in response times between incongnient colour words and colour nonwords when a
single letter is coloured. According to these researchers. these response tirne data provide stronç
evidence that "at least some aspects of word recognition are not automatic" (p. 224)
A Critique of the Besner, Stolz, and Boutilier (1997) Argument
Despite their elimination of the difference between a classic incongruent condition and a
novel control condition by the single letter coloured manipulation. interpreting the Besner et al.
( 1997) results is not as straightforward as it might initially appear. Rather than eliminating the
Stroop effect, it appears as though their particular procedural choices decreased the Stroop effect
substantially (by using manual response and unusual controls). arriving at about 30 ms of
interference. Their single letter coloured manipulation thus only had to remove this remaining
30 ms to produce apparent elimination of the Stroop effect 1.
Manual responding has been shown to remove up to 75 % of Stroop interference relative to
vocal responding (MacLeod. 199 1). A number of studies have demonstrated a reduction in
Stroop interference when manual response is used (e.g., Nielson, 1975: Redding & Ge jets,
lThere is one actuai flaw with the Besner et al. (1997) nudy that appean minor. though its magnitude is nor readily apparent. The authors note that they conmcted their control items using the first two letters of each cotour word. flic control nonword "grend." however. uses the first three letters of the colour word "green." Due to the fact that the present study intends to replicate and estend the Besner et al. (1997) findings, the nonword "grend" wi11 also be used in the present study. For consistency ilth the stated method and the other three control items. an item such as "grond" or "grund" wouid actually have been &ter. 1977). This simple methodological variation can reduce normally large (e.g., 180 ms) Stroop
Reduced Stroop Interference - 20
interference down to 45 ms. Certain control conditions may also appear to reduce the Stroop
effect (e.g.. colour nonwords such as BLAT) given that the Stroop effect has been s h o w to
occur even when only the first letter of a conflicting colour word is presented (Regan, 1978;
Logan & Zbrodoff, 1998). Recall that Besner et al. (1997) constructed their control stimuli
( E T . GREM). YEMLE. and BLAT) "to match the incongruent stimuli on length and on the
first two letters, given the repeated worry that a Stroop effect can result simply from the first two
letters spelling a color word" (p. 223). It is quite unclear how this constitutes a corifrd condition
in that it seems likely, even by the authors' own admission. that interference could also occur for
these new nonword stimuli (Le.. there could actually be interference in the nominal control
condition). Thus, it would be difficult to determine whether response times to stimuli are similar
because interference has been eliminated or because the Stroop effect is occumng for both sets
of stimuli.
In essence, incongrnent colour words and control nonwords may be effectively equivalent if
the first two letters of colour words are the source of the majority of Stroop interference. This
possibility will be considered in more depth when the work of Regan ( 1 978) and Logan and
Zbrodoff (1998) is reviewed. The fact that Besner and Stolz (1999ah) replicated Besner et al.
(1997) does not vitiate this argument given that the same response mode and control conditions
were used. Thus, by using colour nonwords (e.g.. RET and YENILE). and by having
participants respond manually, Besner et al. ( 1997) only had to eliminate a 30-rns Stroop effect.
which is very small when compared to the more typical size of the S troop effect ( 1 80 ms). Were
different controls and vocal responding used, it is quite possible that up to a 150-ms Stroop effect
would still be observed between colour words and nonwords, even if the Besner et al. (1997)
manipulation reduced inteièrence by 30 ms.
Reduced Stroop Interference - 2 1
The critical concem with the Besner et al. (1997) study. however, is their bold theoretical
claim that they have eliminated the Stroop effect. A careful examination of the obtained results
suggests a rather different interpretation. Their reduction in the Stroop effect is derived not from
a decrease in response time for the incongruent Stroop tnals so much as fiorn an increase in
response time for their novel control Stroop trials. This seems countenntuitive because one
would expect that a decrease in Stroop interference would be a function of incongruent response
time decreasing to meet control response tirne. Besner et al. ( 1 997). however, have shown an
increase in the response tirne to the control condition, leaving the incongruent condition
unaffected. This does not necessarily mean that Stroop interference has not been reduced or
eliminated, but it is an unexpected pattern of results and one that certainiy deserves further
scrutiny. It is dificult to view Stroop interference as having been eliminated when response
times for incongruent tnals (the condition responsible for Stroop interference) in both the whole-
word-coloured and single letter coloured conditions are vimially identical.
Collectively, these problems have made several researchers dispute the claims of Besner et al.
( 1997). Studies by Marmurek ( 1999) and by MacLeod ( 1999) have replicated Besner et a l . 3
( 1997) basic methodology but have also included additional conditions, such as vocal responding
and different, more common controls. Marmurek's control stimuli consisted of the animal names
cat. lion. mouse, and rabbit. These controls have the advantage of being words that are identical
in length to the colour names but that decrease the chance of invoking a Stroop effect (although
rabbit does begin with the same letter as one of the colour words). In addition, the words belong
to a single category (animais) as do colour words (colours). Besner et a1.k control stimuli and
button pressing procedure were also used for cornparison purposes. Thus. using a 2 X 2 design,
Marmurek compared the performance of four groups of participants. One group responded
Reduced Stroop Interference - 22
manually (button pressing) to Besner et al.'s (1997) stimuli (colour words and nonwords), a
direct replication of the Besner et al. (1997) study. A second group also used Besner et a1.k
(1997) stimuli, though participants responded vocally to the to-be-identified colour. A third
group responded manually but used the aforernentioned animal word controls. The final group
also used the animal control stimuli but responded orally to the colour.
The results of the Marmurek (1999) study showed that Besner et a1.k ( 1997) apparent
elimination of the Stroop effect was dependent on the modality of response (see Table 4). When
rnanual responding was used, Besner et al.'s ( 1997) reduction of interference in the single letter
coloured condition was replicated. though interference was not completely eliminated. For fully
coloured items. conflict trials took longer to respond to than did control tnals. When only a
single letter was coloured. the difference betwcen conflict and control trials was reduced. This
reduction was açain due to an increase in response time for control trials whereas inconçment
tnals sbowed little increase. Clearly. colouring a single letter led to a decreased amount of
interference between conflict and control trials. It is not clear, however, that the decrease in the
difference between contlict and control trials is due to a reduction of Stroop interference nor that
it always constitutes elirnination. Marmurek's ( 1999) results suggest that the difference between
conflict and control trials in the Besner et al. ( 1 997) study could be attributed to the use of button
pressing. When the entire word was coloured, there was a 42 rns response time difference
between conflict and control trials, with conflict trials taking longer. When only one letter was
coloured. both contlict and control tnals decreased in response time. though there remained a 42
ms difference; far fiom an elimination, if even a reduction. of Stroop interference.
When Marmurek ( 1999) switched to his own controls (animal names). a similar if not more
stnking pattern of results occurred. With manual responding. there was a 38 rns difference in
Reduced Stroop Interference - 23
Table 4
Mean Response Times lin ms) to Name Colour as a Function of Condition (AI1
Letters Coloured vs. Single Letter Coloured) Across Four Grou~s (Vanine
Remonse Mode and Controls) From Mannurek ( 1999).
Ai1 Letters Colored Single Lctter Colourcd
Triai Type Incongruent ControI Difference Incongruent Control D ifference
Manual response. nonword controls (Besner et al. replication):
RT 882 83 9
Manual remonse, animal word controls:
RT 789 75 1
Orai response. nonword controls:
RT 758 711
Oral reswnse. animal word controls:
RT 823 709
Note: RT = response tirnes
Reduced Stroop Interference - 24
response tirne between conflict and control trials, with conflict trials taking longer. This
difference decreased to 25 ms when only a single letter was coloured. al1 attributable to increased
response time in the control condition. In the oral response situation, the difference between
conflict and control trials was 1 14 ms when the entire word was coloured. When only a single
letter was coloured, conflict trials decreased in response time by 3 1 ms. though there was still a
substantial difference of 77 rns between contlict and control trials. These results certaidy do not
indicate rlimitiatiori of the Stroop effect. Once again, the diminished difference reflects slower
responding in the control trials in the single letter coloured condition.
Besner et al. (1997) seem to be correct that the difEerence diminishes by 30 ms in moving
from fully coloured to single-letter coloured items. and this seems to be fairly consistent across
response mode and control type. The question rernains. though. as to how this reduction relates
to interference. More critically, their strong daim of eliminating Stroop interference is not
supponed. Besner et al. ( 1997) had stated that their "results are consistent with the claim that it
is possible to prevent the computation of semantics." thereby leading to an elimination of Stroop
interference (p. 224). The Marmurek (1999) results, however. are contrary to this argument
because the colouring manipulation did not prevent sernantic cornputation, nor did it lead to
elimination of' t he S troop effect .
MacLeod (1999) has also replicated the Besner et al. ( 1997) study, again exarnining different
controls and modes of response. Although independent. the MacLeod (1999) study was also a 2
X 2 design crossing mode of respondinç with type of control item. Here. however, different
controls were used: Repeated letter swings (www, m. sssss, mrnmmmm) as opposed to animal
words or colour nonwords. In a sense. whereas Marmurek ( 1999) moved "up" fiom Besner et
a h (1997) colour nonwords to real noncolour words. MacLeod (1999) moved "down" to real
Reduced Stroop Interference - 25
nonwords.
There is a wide-ranging debate in the Stroop literature as to what constitutes an appropnate
control (cf. MacLeod. 199 1). It has been argued that such letter stnngs are less word-like and
therefore. not a domain-appropriate control for comparison with words (Besner et al.. 1997). On
the other hand. many forms of words and nonwords have been shown to produce Stroop
interference (e.g., Dalrymple-Alford, 1972. Klein. 1964). making it difficult to distinguish a
reduction in intei-ference on a confiict trial fiom an increase in interference on a control trial (see
Besner et al.. 1997). For this reason. there is no universally agreed upon control type. though by
including the letter stnngs condition. MacLeod (1999) contributes to an overall clearer picture of
the effect of colouring a single letter of a control relative to colouring the entire item.
Theoretically. any difference between the results of MacLeod ( 1999). Marmurek ( 1999). and
Besner et al. (1997) can be attributed to differences in the control stimuli (letter stnngs vs.
animal words vs. nonwords) because al1 other features of the methodology (button pressing).
colour words, and presentation order (randomized) were held constant. Clearly this will not
solve the argument as to the appropriate type of control stimuli to use in Stroop studies. though it
does ailow for comparison as to the different levels of interference each control condition might
produce.
The MacLeod (1999) results are presented in Table 5. It is not necessary to explicitly outline
the results of al1 four conditions. because they are comparable to Marmurek's (1999) four
conditions. It should simply be noted. however, that MacLeod (1999). despite obtaining a
perfect replication of the Besner et al. (1997) results in the comparable ce11 of his 2 X 2 design.
clearly did not eliminate interference when vocal responding and different controls were used.
Despite a decrease in response time in codict trials as well as an increase in response time in
Reduced Stroop Interference - 26
Table 5
mea an Res~onse Times (in ms) to Name Colour as a Function of Condition
(ALI Letten Coloured vs. Sin& Letter Coloured) Across Four Groups
f Vaning Remonse Mode and Controls) From MacLeod (1990).
Al1 ~etk&olored
Trial Type Incongruent Control Difference
Single Letter Coloured -
Incongruent Control D ifference
Manual response. nonword controls (Bcsner et al. replication):
RT 73 3 700 33
Manunl response. animal word controls:
RT 7 43 696
Oral remonse. nonword controls:
RT 778 728
O n l remonse. animal word controls:
Note: RT = response times
Reduced Stroop Interference - 27
control trials, there was still a substantial difference between the two conditions in al1 but the
Besner et al. (1997) ce11 of his design. indicating reliable Stroop interference. even in the single
letter coloured condition.
Collectively, the works of Besner et al. (1997). Marmurek (1999), and MacLeod ( 1999)
indicate that the Stroop effect is not eliminated by colouring only a single letter. contrary to the
claim of Besner et al. (1997). This holds true for the nonwords condition used by Besner et al.
(1997), the animal words used by Marmurek (1999). and the letter strings condition used by
MacLeod ( 1999). .Mthough these researchers successfully replicated Besner et al.'s ( 1997)
pattern of results under precisely the conditions they used. these newer data have in no way
provided evidence that the Stroop effect was eliminated. In fact. when responding is made vocal
rather than manual, there is a substantial Stroop eRect observed in the single-letter coloured
condition. In al1 three studies. however. the consistent finding has been that the control condition
rises by about 20-30 ms when only one letter is coloured. Unquestionably. this is an interestinç
result just not necessady the elimination of Stroop interference that Besner et al. (1 997)
interpreted it to be. Thus. the pnmary purpose of the present research was to better understand
the manner in which Stroop interference is reduced in Besner et al.3 ( 1997) sinçle letter
coloured condition. In addition. the present research will try to determine why a 30 ms increase
in response time is observed in every condition except the classic incongruent condition.
Interpreting the Apparently Reduced Interference in the Single-Letter Coloured Condition
There are a number of possible explanations for this apparent decrease in Stroop interference.
though there is currently no evidence to uniquely confirm any one of these explanations. One
possibility is that response times to colour words in the single-letter coloured condition do not
increase. perhaps due to a ceiling effect in the fùlly coloured condition, not to a reduction in the
Reduced Stroop Interference - 28
Stroop effect. If response times for colour words in the incongrnent condition were at a ceiling
level when hlly coloured, then the letter search manipulation could not lead to an increase in
response time above that level. This would explain why the letter search task can consistently
lead to an increase in response time for control stimuli but no such response increase for colour
word trials (which always demonstrate the highest response times when al1 letters are coloured).
It seems unlikely, however. that a ceiling effect would explain the results of al1 three expenments
reviewed thus far (Besner et al.. 1997, MacLeod, 1999: Marmurek. 1999) in that response times
of 750-800 ms are not particularly high when one considers individual differences (response
tirnes ranging fiom 1000-1200 ms are not unheard of). Response times would need to be more
inflated before it could be concluded that response time was at a ceiling levei.
A second possibility could be that the contrast between the coloured letter and the rest of the
letters in the word is critical, a type of pop-out effect (see. e.g., Treisman & Gelade. 1980). For
example. the colours red and blue are fairly discemible €rom the colour white when being viewed
on a black background whereas the colours yellow and green do not stand out as much. Thus.
when the coloured letter is red or blue it might stand out more from the irrelevant word making
the irrelevant word easier to ignore (and perhaps, less wordlike). Yellow and green letters may
blend into the white type. however, making it difficult for the participant not only to identiQ the
display colour. but also to ignore the irrelevant word as its integnty is fairly well maintained.
Thus, it might be possible to alter performance on the Stroop task by varying the background
colour or the brightness and hue of the colour displays.
Unfortunately, there is nothing in the literature to suggest that either of these two factors is the
key variable. Besner et a1.k (1997) "semantic blocking" explanation for these eKects is
interesting, though there are some difficulties associated witn generalizing semantic piiming
Reduced Stroop Interference - 29
explanations to the Stroop effect, as outlined in the following section. Nonetheless, I would like
to propose an alternative account for these results that does not necessarily involve the
"blocking" of irrelevant words: Rather. 1 would argue that these results likely point to the
influence of two processes. In taking this stance. it is necessary to believe that Besner et a1.k
(1997) account is partially correct and that it is not merely the control trials that are slowing
down when a single letter is coloured: rather, everything slows down and the response time data
indicate a true reduction in Stroop interference masked by overall slowing of equivalent
magnitude.
There is a distinct possibility that when an individual processes a word with a single letter
coloured (and al1 other letters appearing in white pnnt), they do so differently than if the same
word appeared entirely in a single ink colour. This is not to say that the individual does not read
the word: rather. colouring a single letter may make a word appear unique or less wordlike. If
this is the case, such differential processing rnay lead to a decrease in Stroop interference of
about 20-30 ms. This 20-30 ms reduction in Stroop interference is then likely offset by an
increase in the time that it takes to identiS, the coloured letter because the individual is forced to
search for the coloured letter which varies in position randomly from trial to trial. When the
entire word is coloured, however, it does not matter where in the word an individual Iooks
because every letter position will provide the desired colour response information.
For example, if the first word a participant encounten is a four-letter word with the founh
letter coloured, the participant would have to search for that coloured letter. Once the colour
letter has been identified, the participant would either remain fixated on that position on the
screen or return to the fixation position. In either case, if the next word that appeared was a fully
coloured word, no search time would be necessary and a response could be made irnmediately.
Reduced Stroop Interference - 30
If. however, the next word that appeared was a five letter word with the second letter coloured,
then the participant would again have to engage in another search, thus increasing the time
necessary to make a response. The letter search might in tum iead the participant to process the
distractor word differently, thus leading to a decrease in Stroop interference. This explanation
does an adequate job of accounting for the finding that Stroop interference was decreasing due to
an increase in control response times as opposed to a decrease in response times in the
incongrnent condition. Essentially. incongruent response times stay the same when a single
letter is coloured because the extra time to search for the coloured letter is offset by a decrease in
Stroop interference, which makes it seem as though the times do not change in switching from
fûlly coloured words to single letter coloured words. In the control condition. there should
(ideally) be no Stroop interference and therefore. only the increase in search time affects the
colour naming response. Henceforth. this explanation will be referred to as the two-process
account.
The two-process account implies that a reduction in Stroop interference occun when a single
letter is coloured. It is dificult to accept Besner et al.'s interference elimination conclusion,
however, based solely on similar response times in the incongruent and control conditions of
their study. To argue that the Stroop effect has been eliminated. it would be necessary to show
that the distractor words in Stroop trials are not being read. Besner et al. (1997) have suggested
that colouring a single letter tums the Stroop task into a lerter search task, thus disrupting
semantic processing of the distractor word. Their inference is that this letter search task has
prevented participants from reading the distractor words and, thus, from processing the semantic
properties associated with these words. In a sense then, they are suggesting that colouring a
single letter causes the individual to treat the word as though it is not actually a word. It is
Reduced Stroop Interference - 3 1
difficult to make this argument relying solely on response time data, however. as response time
is an indicator of how quickly participants performed the colour naming task and provides no
information as to whether distractors were read. That distractors are not being read has been
inferred due to equivalence in response times. but no explicit demonstration has been made to
show that colouring a single Ietter causes participants to break words down into their individual
letter components. Thus hrther evidence is needed to corroborate Besner et a1.k (1997)
response time data.
Why the Reduction and Elimination of Semantic Priming May Not Generalize to the Stroop Effect
As was suggested earlier, the evidence is not strong and at best indirect for Besner et a1.k
( 1 997) claim that colouring a single letter blocks semantic processing while simultaneously
enhancing processing at the letter level due to feedback from the lexical level. Without such
evidence, the appropnateness of this rather complex expianation is difficult to judge. Moreover.
as in Friedrich et al. (199 l), semantic primes are usually presented to the participant pior to the
target stimuli. In Stroop research, however, and particularly in the Besner et al. (1997) study, the
distractor item (the colour word) is presented simultaneously with the stimulus that requires a
response. Presenting distractors simultaneously rather than in advance is likely to affect the
rnanner in which a panicipant orients to a task. As an example. if the distractor word in a Stroop
task were presented prior to the presentation of a display colour, participants could employ a
strategy that would enable them to ignore the distractor prior to display colour presentation. At
the very least, presentation of a distractor p ior to a target may provide participants the time
necessary to process and then block the distractor. When distractor and display colour are
presented at the same time, however, simultaneous demands are placed on the participant.
making it harder to ignore the distractor. Thus, a different type of strategy may need to be
Reduced Stroop Interference - 32
adopted rather than ignonng (or processing and then blocking) the first stimulus presented.
Indeed, a nurnber of studies have been reported in which the stimulus onset asynchronies (SOA)
of distractor word and display colours were vaned in the context of a Stroop task. Although
Stroop interference is always observed, different patterns of interference are observed (generally,
a decrease in interference when irrelevant colour words are presented pnor to the colour display)
as a function of different SOAs (e-g. Dyer, 1974; Glaser & Glaser. 1982; Koch & Brown, 1994;
MacLeod & Hodder, 1998: Sugg & McDonaId, 1994; see MacLeod. 199 1, for a review).
Aiso. certain words are more Iikely to be facilitated by a prime stimulus than are other words.
In the earlier example, the word "nurse" is facilitated to a greater degree by the word "doctor"
than by the word "stethoscope." This is due to the higher degree of association between the
words "nurse" and "doctor" relative to the words "nurse" and "stethoscope." In Stroop studies.
however. the colour words used are al1 very highly associated with each other and to the concept
of colour. For this reason. even if a reduction in semantic pnming were observed for a letter
scan task, it is doubtful that the semantic properties of the colour words could be ignored on
every trial. Although various researchers (e.g., Fnedich et al.. L 99 1 ) have s h o w that the effects
of semantic primes can be reduced and in some cases eliminated. no researcher has shown that
the pnming effects of such highly related words can be eliminated al1 of the time, particularly
with such a tiny stimulus/response set as is the case in the standard Stroop task. Due to the
strong semantic relation among colour words, as well 3s to the fact that each word is presented
numerous times. it is unlikely that the semantic relation between these words could be absoluteiy
ignored. This is evidenced by the fact that when vocal responding is used in the Besner et al.
( 1997) task a Stroop effect does occur (Macleod, 1999; Marmurek, 1999). indicatinç that the
semantics of the colour words have been computed. Finally, as has been previously noted. there
Reduced Stroop Interference - 33
are a number of documented ways to reduce the Stroop effect (e.g., manual responding), which
are not necessanly relevant to semantic priming (see Sharma & McKema, 1998). Besner et al.
(1997) have employed two of these methods in their study: manual responding, and items that
produce interference in the "control" condition.
When letter search was examined by Marmurek (1999) and MacLeod (1999) with vocal
response and different controls. a substantial Stroop effect was still observed despite the
reduction of Stroop interference by 30 ms. Clearly, the colour word is being read in the
Marmurek (1999) and MacLeod (1999) studies. showing that semantic pnming occurs in at least
some, if not most, situations even when a Ietter scan task is used. It should be noted. however,
that Besner et al. (1997) are correct in stating that words are not always automatically read.
CIeariy there are many situations in which word reading is not necessary or would even be
detnmental. As an example. consider an individual who scans a dictionary to find a definition
for a cenain word. On a single page of a dictionary there are numerous words and definitions for
these words. The individual does not. however. automatically read every single word on the
page as this would be a great waste of time. Rather. they quickly scan until they find the word
for which they are seeking a definition. perhaps reading (automatically or otherwise) only a few
other words during the search.
Automatic effects must be contemually bound, with the previous example providinç a
situation in which al1 words are not automatically read. Aithough words are not always
automatically read, however, Besner et al. ( 1997) provide insufficient proof to support the daim
that colour words are not being read in their letter scan condition. Simple response time data are
not enough to prove that a word has not been read and that the semantics of the word have not
been encoded and understood. Response time data solely indicate how long participants take to
Reduced Stroop Interference - 34
colour name when a single letter is coloured, they do not provide an unarnbiguous rneasure of
whether distractors are read. It is appropriate to use response time in studies of semantic priming
as there is an expected response benefit of having previously seen a related word. An absence of
this benefit would indicate that the prime word had not been read. In Stroop studies. however.
one cannot argue that an equivalence in response time between incongment colour words and
colourlike nonwords is indicative of distractors having not been read. Other possibilities exist.
An equivalence in response time rnay be the result of both distractor types being read and
producing approximately equal interference. Such an equivalence could also be caused by more
than one process contributing to response tirne in the Stroop task. This is the basis for the two-
process account that I have outlined.
It has already been suggested that Besner et ah's (1997) original Stroop effect was quite
small. and likely due to a number of other methodologicai choices they made (e-g.. manual
response. novelcontrol condition). Thus. rather than trying to account for a complete elirnination
of the Stroop effect, it seems more reasonable to atternpt to account for the approximatcly 20-30
rns of decrease in Stroop interference that is observed when only a single letter is coloured. The
two-process account explains this decrease nicely. and will receive further scmtiny in the present
thesis.
Thus far, however. there has been a key omission in the discussion of factors that may have
infiuenced the results of Besner et al. (1997): the possible influence of the position of the
coloured letter when irrelevant letters appear with only a single letter coloured. 1 will now
review the relevant literature that suggests that the first letter of an incongment colour word may.
in and of itself, produce Stroop interference. Following this, the NO-process account will be
extended to allow for an investigation of the position of the coloured letter under this Framework.
Reduced Stroop Interference - 35
Is Encoding the First Letter of an Incongruent Colour Word Al1 That is Necessary to Invoke a Stroop Effect?
The influence of the position of the single coloured letter has yet to be investigated but.
according to the preceding logic, this may be crucial. Experiments by Singer, Lappin. and
Moore ( 1975) and Regan (1 W8), as well as recent research by Logan and Zbrodoff ( 1998). have
suggested that the first letter of an incongment colour word may be al1 that is necessary to invoke
a full-blown Stroop effect. This idea was first put forth over 25 years ago by Singer et al. (1975)
who examined the potential difference in Stroop intederence when the to-be-named colour
appeared in the first. middle. or last two letters relative to the entire word being coloured.
Aithough the greatest Stroop interference was observed when the entire distractor word was
coloured. there was also an effect whereby the first letters of an incongment colour word
interfered more than did the letrers in the rniddle or at the end of that word. This finding was
confirmed by Regan (1978). who demonstrated a delay in colour naming when only the first
letter of an incompatible colour word was presented as a distractor.
Regan (1978) designed a study to investigate the efFect of presenting only the first letter of an
incongment colour word afier previous researchers had demonstrated no Stroop interference for
colour words relative to colour-word anagrams (e-g.. BELU). which were used as control stimuli
(Hintzrnan et al., 1972). She argued that the colour-word anagrams may have been encoded in a
meaningful manner by panicipants despite their apparent lack of meaning. Thus, Regan sought
to investigate whether these effects would generalize to single letters:
Single letters per se are irrelevant to color naming. If al1 the stimuli are single letters and the task is to name the color of the ink in which a letter is pnnted. participants should be able to ignore the letters. However, if these familiar stimuli are processed automatically and if those letters that are color-name initials interfere with or facilitate color naming, it would be even stronger evidence in suppon of the
Reduced Stroop Interference - 36
involuntary nature of the processing of familiar items ... .If such an effect occurs, it would further indicate that ... the way such an item is processed may (be determined) by the way its processing fits into the overall computation required by the task. (P. 134)
Regan discovered that the first letter of incongruent and congruent colour words led to a pattern
of Stroop interference and facilitation similar to other studies in which entire colour words were
presented: "Aithough letters alone may not elicit color names as primary associates. given the
color-naming task they are processed in relationship to color names" (p. 135). This point is also
highly relevant to my previous critique of Besner et al.'s (1997) controls as inappropnate: Given
the colour-narning task, colour nonwords may have been encoded in a meaningful rnanner and.
consequently may have elicited Stroop interference. Though Regan's ( 1978) work is very
important to the present thesis. little attention was given to this line of research until Logan and
Zbrodoff ( 1 998) recently reponed a very related finding.
Logan and Zbrodoff(i998) examined the size of the Stroop effect with different modalities of
response: vocal. button pressinç. and typewritten responses. In the latter case. participants had to
actually type out the word corresponding to the colour of ink in which colour words appeared.
Only the first and last of their experiments are relevant here. Their first expenment was a simple
Stroop study with three groups, corresponding to the three response modes just mentioned.
Logan and Zbrodoff s reason for including the typewritten response section was simple: By using
button pressing as a modality, researchers leave open the possibility that the decrease in
interference is due to transfer inappropriate processing rather than to a decrease in the effect of
automaticity. It is difficult, therefore, to determine whether button pressing leads to a decrease in
interference due to a dissociation of response (an arbitrary bunon press representing a colour
rather than a colour word response) or to an increased response time due to a legitimate decrease
Reduced Stroop Interference - 3 7
in the effect of automaticity (e.g., such as the notion that semantic priming can be disrupted
when a letter search task is applied to a prime word). The typewritten response. on the other
hand. has the benefit of being similar in response modality to button pressing and similar in
automaticity to vocal response. In addition, for experienced typists (which Logan and Zbrodoff
used). typewritten responses should be approximately as automatic as vocal responses. Thus,
their incorporation of typewritten response provides a good test of whether response differences
are due to response modality rather than to automaticity:
If the difference was due to response modality. then the typewritten Stroop effect should be no larger than the arbitrary-keypress Stroop effect. If the difference was due to automaticity. then the typewntten S troop effect should be as large as the vocal Stroop effect, and both should be larger than the arbitrary keypress. (P. 98 1 )
Logan and Zbrodoff(1998) were also interested in the response time of typewritten responses as
a function of congruity. In other words. would typewritten responses be more rapid when Stroop
trials were congruent relative to incongment trials. where the incompatible colour word could
irnpede typing speed?
The results of their first experiment demonstrated a larger Stroop effect for typewritten
responses relative to vocal and keypress responses (see Table 6). There was a 62 ms difference in
response time between typewritten responses and the next longest condition, arbitrary
keypresses. It is of interest, however. to note that the longer response times in the typewritten
response condition were not attributable to the length of time that it took to type an entire
response. but rather to the length of time it took to make the first keypress of the response. Thus.
if the ink colour to be typed was "red." the word "red" was typed at an equal rate in al1 three
conditions. In typewritten responses to the incongment condition, however, participants
dispiayed a greater delay in onset response time before typing the letter "r."
Reduced Stroop Interference - 3 8
Table 6
Mean Remonse Times (in ms) to Name Colour as 3 Function of Remonse Mode
(Vocal vs. Kehpress vs. T\.pewritten) From Logan and Zbrodoff ( 1998).
Response Mode
Keyp ress
Esperiment One (3 response modes. incongrnent colour words)
Colour Word RT Y 12 96 1 1023
Esperiment Ttvo (T>pe~vtitten response. incongruent colour words vs. incongrnent single letters)
Colour Word RT NIA NIA 1032
Single Letter RT NIA NIA 1 0 16
Note: RT = response times
Reduced Stroop Interference - 39
This typewritten response pattern led Logan and Zbrodoff (1998) to investigate the idea that
an incongment single letter was al1 that would be necessary to produce a Stroop effect. In their
third experiment, they exarnined the difference in Stroop interference for typewitten responses
of an entire colour name relative to just the first letters of colour names. The resuits of the
experiment demonstrated that there was an approximately equal amount of Stroop interference
for both incongruent colour names (RED in green) and incongment single letters (R in green).
There was only a 16 ms difference between typing times for the two conditions (10 16 ms for
single letters and 1032 ms for colour words). which was not a significant difference. Thus.
Logan and Zbrodoff (1 998) suggested that the observed equivalence in Stroop interference
implies that al1 letters after the first letter of an incongment colour word have iittle. if any. effect
on the magnitude of Stroop interference.
Thus far, the concepts of automaticity. the Stroop effect. and semantic priming have been
considered. Studies have been reviewed which demonstrated a reduction in and/or an
elimination of semantic priming effects. These studies served as the basis for Besner et al.'s
(1997) experiments in which they claim to have eliminated the Stroop effect. It has been argued
that Besner et a1.k ( 1997) explanation is not without cornpetitors and that their data do not
necessanly demonstrate the elirnination of the Stroop effect. A number of the elements of the
Besner et al. ( 1997) study have been outlined which may explain their apparent elirnination of
Stroop interference in ways other than the way they espouse. A two-process explanation was
also introduced to account for the results of Besner et al. (1997). Finally. research was reviewed
that suggests the imponance of the first letter of an incongment colour word in producing Stroop
interference. To this end. there is another possible explanation for the Besner et al. (1997) data.
which is a closely related to the two-process account. This should not be viewed as a separate
Reduced Stroop Interference - 40
explanation for the Besner et al. (1997) results so much as an extension of the already outlined
two-process account.
An Extension of the Two-process account: WiIl Letter Position Influence Response?
The design of Besner et al.'s (1997) second experiment was within participants and,
therefore, participants were exposed to every condition (single ietter word. single letter nonword.
fully coloured word, fully coloured nonword) in a mixed fashion. Had participants received ody
hlly coloured words. it would be possible to constantly fixate on any part of a word or nonword
because each position would provide the desired response. This is not possible. however, in the
single-letter coloured condition because fixating on any given point will not provide the relevant
information al1 of the time. To compensate for this. the participant has to find the easiest rnethod
to identify the colour of the stimuli across al1 trials.
It is likely that scanninç each word or nonword from left to right would be the rnost "natural"
method to arrive at a response. Under this scenario, if the entire word is coloured. then the
participant can respond to the colour afier scanning to only the first letter. If a single letter is
coloured, then the participant must scan from lefi to right until the coloured letter is observed.
Thus, faster response times would be observed for a single letter coloured at the beginning of a
word than for a single Ietter coloured toward the end of a word. In addition. response times for a
single letter coloured at the beginning of a word relative to words which appear entirely in colour
should be approximately equal due to being able to respond after scanning across to the first
letter in either case.
The results of Besner et a1.k (1 997) second expenment can be interpreted in the following
manner. assurning that participants are scanning left to right so as to locate the colour to be
named. In the fully coloured incongrnent condition. participants are able to respond to the colour
Reduced Stroop Interference - 4 1
after they have processed the first letter. When the colour to be named can be processed
immediately, this does not necessitate breaking the word down into individual letters. Indeed, a
response can be made before individual letters have been processed and rejected, leaving the
entire word intact. This increased the likelihood that the word would be viewed as a whole.
Therefore, when the stimuli are colour words, the word interferes with colour naming, creating
Stroop interference. When the stimuli are not colour words. however. Stroop interference
ostensibly does not occur because nonwords are less likely to provide interference relative to
colour words. Thus, colour naming is achieved 30 ms more rapidly when a colour nonword
(Besner et al.'s RET-type control) is presented relative to when the coloured stimuli are actual
colour words.
Consider, however, the single-letter coioured condition. Here, the word is broken down into
its individual letter components and the individual scans left to right until the coloured letter is
encountered. If the coloured letter were the first letter encountered, then equal Stroop
interference should occur in both the coIour nonword control and the colour word, consistent
with the findings of Logan and Zbrodoff (1998). If the coloured letter is not the first letter. then
the expected pattern of Stroop interference is less clear-cut. As words are broken down into their
single-letter components, this increases the chance that the words will be processed differently.
This logic is similar to that of Besner et ai. (1997). though there is currently no need to suggest
that this differential processing necessitates that the distractor is not read. There should be an
increase in response time, however, due to the extra time it takes to scan across the tarset
stimulus until the coloured letter is encountered. Thus. the 30 ms of response time that would be
added due to scanning for a single letter is counteracted by a reduction in Stroop interference
when the coloured letter is not the first lener. This does not suggest an elirnination of the effect:
Reduced Stroop Interference - 42
Stroop interference rnay still be highly prevalent when the first letter encountered is the coloured
letter (in accordance with the prediction of Logan & Zbrodoff. 1998) and perhaps to a lesser
degree when subsequent letters are coloured. This strategy of scaming left to right until the
coloured letter is encountered seerns reasonable as it would lead to a response afier o b s e ~ n g the
Srst letter on more than 50 % of the t d s (e.g.. every trial in the fully coloured condition as well
as any time that the first letter is coloured in the single-letter coloured c o n d i t i ~ n ) ~ .
Under this explanation, there are three possible pattems of Stroop interference that could anse
for coloured letters occumng afier the first letter. These pattems are outlined in Figure 1.
assuming that the stimulus is the 6-letter word YELLOW printed in red. Similar functions could
be displayed for shoner words. One possibility is that as long as the coloured letter is not the
first letter, no Stroop interference should occur (LA) . This would suggest that the moment a
word is broken down into its individual letter components, it is no longer viewed as a meanineful
whole. thus preventing Stroop interference. This logic is panially in line with Besner et al.'s
(1997), though they did not explicitly take into account the importance of the position of the
coloured letter in that study or in any of their subsequent studies.
A second possibility is that more Stroop interference would be observed for coloured letters
appearing eariier in a word relative to coloured letters occumng later in the word ( 1 -B).
The third possibility is that when the first letter is not the coloured letter. greater Stroop
ULogan is correct in assuming tlint the first letter of a confhcting colour word is al1 that is needed to invoke a Stroop effect, then it might be eqxcted tliat there would be equai Stroop interference betwecn the conflict and control trials when the entire word is coloured. This is not thc case. hotvever: Besner et al. ( 1997). Marmurek (1999) and MacLeod (1999) al1 observe an approximate 30 ms Merence between confiict and control trials when Besner et a1.k methodolog-. is replicated. There is no clear espimation for this difference in pattern in Logan's research. There is. hotvever. the possibility that colouring a single letter makes a word appear less wordlike and as such forces the individual to deal with the stimuli on a letter by letter basis. Unfortunatel-. there is no esisting evidence for tiiis in the litenme.
Amount of interference (in ms)
Amount of interference (In ms)
Amount of interference (in ms)
Reduced Stroop Interference - 43
Figure 1: Possible patterns of Stroop interference as a funcüon of the position of a single coloured Ietter (assuming that stimulus word is six letters long ... e.g., YELLOW)
Position of the single coloured lettet
1 2 3 4 5 6
Position of the single coloured letter
Reduced Stroop Interference - 44
interference would occur for coloured letters O C C U ~ ~ ~ later in a colour word as opposed to
earlier (1-C). Even though the word itself has been broken d o m into its individual letter
components, larger Stroop interference may be registered when more of the word has to be
scamed to find the coloured letter, analogous to a letter-by-letter reading strategy.
There is no evidence in the literature to support any of these daims; the influence of the
position of the coloured letter remains an empirical question. The concept of dealing with letters
irdividrraliy is important because this is what is thought to decrease or eliminate the Stroop effect
as it did in semantic pnrning expenments (e.g.. Friedrich et al.. 1991). The importance of the
position of the coloured letter, however, has not been given any explicit pnor research attention.
Consequently. the proposed research will focus initially on the position of the coloured lerter and
its corresponding response. [t seems certain that the first letter of a conflicting colour word will
produce interference. but the influence of the position of the colour on the remaining letters is
not as clear-cut. As just outlined. there could be no difference in interfierence between the
remaining letters (al! showing relatively little) or there could be an increase or decrease in
interference for letters which occur later in a word relative to letters which occur earlier in a
word. As one goal. the present study will for the first time examine the pattern of response times
dependent upon the position of the coloured letter.
The Need for a More Explicit Test of Whether Distractors are Read
To argue that Stroop interference has been eliminated, it would be necessary to show that
the word in Stroop trials has not been read, given that the Stroop effect rests on the notion that
the irrelevant word is automatically read and interferes with the colour naming response. Besner
et al. (1 997) argued that they had eliminated the Stroop effect but did not directly show that the
word had not been read, instead relying on the equivalence in response times to support their
Reduced Stroop Interference - 45
argument indirectly. Critically. they did not remark on the apparently increased control
condition times. 1 have already argued that simple response time data are not necessarily
indicative of whether irrelevant words have been read, as there are numerous factors that can
influence participant response. 1 have also outlined previous research that suggests that
irrelevant words are likely still being read when a single letter is coloured. even if this colour
manipulation leads participants to process distractors differently than they would if they
appeared fùlly coloured. To further emphasize this point. 1 will now briefiy review a few
relevant findings.
Friedrich et ai. ( 199 1 ) have already shown that identity priming remains when a single letter
is searched for. even though semantic priming is disrupted. kueger and Weiss (1976) have also
shown letter search effects that indicate that nontarget letters are still being attended to. Across
three experiments, t hey observed faster search times for fixed position target letters in words
relative to nonwords. This finding also held when participants searched for the presence vs.
absence of a target letter in words vs. nonwords. The inability to disrupt the word superiority
effect - the effect whereby "participants are reliably faster and more accurate in letter
identification if the letter appears within a word" (Reisberg. 1997. p. 47) - on any level suggests
that words and nontarget letters are still being perceived. despite their irrelevance to the letter
search task (Knieger & Weiss. 1976). Thus. it is highly likely that colour words are being read
in the Besner series of studies, even if the possibility exists that they are being processed in a
different manner than they would be had al1 letters appeared in colour. In addition, the limited
set of words used in Stroop studies means that these words are presented to participants on
multiple trials and are even primed by the corresponding to-be-named colours. It is likely.
therefore, that enhanced repetition priming woiild occur relative to Friedrich et a1.k (1 99 1) smdy
Reduced Stroop Interference - 46
in which participants ody saw each target word. Clearly. there is ample evidence to suggest that
distractors are likely read, even when a single letter is coloured. Nonetheless, we are unable to
speak of the fate of the Stroop effect without a more explicit test of whether distractors are being
read when a single letter is coloured. Thus, the main focus of the present thesis will be to
provide an explicit test of the manner in which irrelevant words are processed when they appear
on a Stroop trial with a single letter coloured.
Negative Priming?
One way to examine whether a word has been read would be to examine negative priming
trials in the Besner et al. (1997) and Besner and Stob (1999db) studies. Negative priming refers
to slowed processing on a second trial when the required response is that which was suppressed
on a first trial. This effect was first observed within the context of a Stroop study (Dalrymple-
Aford & Budayr. 1966). For example. if a participant receives the word GREEN in the colour
blue (say "bluet') on one trial and then receives any other colour word in the colour green (say
"green") on the following trial, they will be slower to respond than if the colour to be named on
the second trial was anything other than that which was suppressed initially (green). Negative
priming occurs because the individual read the word GREEN on the first triai and understood not
to respond to it. Thus. when required to respond to the colour "green" on the subsequent trial.
their suppression of the word on the previous trial interfered with their response to the colour.
thus indicating that a semantic connection was made (see Fox. 1995 for an in depth review of the
negative priming literature).
If participants in the Besner et al. (1 997) study were slow to respond to negative priming trials
on which a single letter was coloured, it would demonstrate that distractors are being read.
Undoubtedly there would be a number of negative priming trials in the Besner et al. (1997) data
Reduced Stroop Interference - 47
due to the small stimulus set and large number of trials. Negative priming trials could also be
used to investigate whether the Besner et al. (1997) colour nonwords elicited Stroop interference.
If they did. then slowed responding would be expected if. for example, participants saw RET in
green (say "green") followed by BLLJE in red (say "red) relative to BLUE in yellow (say
"yellow"). The slowed response would occur because suppression of the word RET might be
functionally sirnilar to suppression of the word RED. Unfortunately. we do not have access to
the Besner et al. (1997) data to search for negative priming trials.
As it happens, Besner (2000) himself has recently perfiormed a negative priming study using
his single letter coloured manipulation:
the elimination of a Stroop effect does not speak to the ultimate fate of the irrelevant word. One way of determining whether the irrelevant word ever gets processed despite the absence of a Stroop effect is by examining whether there is a negative priming effect.
(Besner. 2000. p. 4)
Besner used a number of different procedures in an attempt tu prevent panicipants from reading
irrelevant words ( e g spatial cueing. colounng a single letter) and then tested whether negative
priming would occur. a certain indicator of whether words are being read. In a single
expenment. he employed three groups of participants, each of whom completed a slightly
different Stroop task. The first group identified the colour displays of irrelevant colour words in
which al1 words appeared fully coloured (50% congruent trials, 50% incongment trials) and with
al1 letters spatially cued by a small arrow (similar to the cueing procedure from Besner & Stolz,
1999db). 125 ms pnor to the appearance of the stimulus. This group served as the baseline
condition. The second group identified colour displays of irrelevant colour words (50%
congruent trials. 50% incongment triais) in which a single letter appeared in colour and dl other
letters appeared in white. On every trial. the coloured letter was cued, again using a small arrow.
Reduced Stroop Interference - 48
Finally, a third group completed the same task as the second group. with the sole exception being
that the proportion of congnient to incongment trials was altered in an atternpt to discourage
participants fiom reading colour words (as previously explained. congruent trials may encourage
participants to read distractors as they provide the desired response). Thus, only 20% of trials
were congruent whereas 80% were incongment. As in previous experiments. there were four
display colours (red, blue, yellow. and green) and their corresponding colour words served as
distractors. The response buttons were also the same as in al1 previous experiments in the Besner
et al. series. Al1 participants cornpleted 40 practice trials followed by 120 experimental trials.
The results of the experiment are presented in Table 7 and again it appears as though the
single letter coloured manipulation led to an elimination of Stroop interference. There were 93
rns of Stroop interference in Group 1 but only 1 rns of interference rernained in Group 33 .
It is encouraging to the argument of Besner et al. (1997) that this experiment provided another
replication of the effect of the single coloured letter manipulation on Stroop interference. When
Besner (2000) cornpared response times on negative priming trials to non-negative pnming
trials. however. non-negative priming trials were responded to 52 rns more quickly than negative
priming trials. This would appear to be quite strong evidence that words are being read
autornatically dunng the Stroop trial and that the irrelevant response is suppressed. thus ieading
to a difficulty in responding to the previously suppressed response on the trial that follows. The
existence of negative priming here would therefore appear to be inconsistent with the Besner et
al. account.
Intnguingly. Besner (2000) offers a different interpretation of these results, suggesting that
%t should be noted that it may not be entirely appropriate to use Gmup 1 as a badine cornparison for Croup 3. A more appropnate cornparison would be a fourth group where the entire irrelmant word appeared firlly coloured and 20% of trials were congruent whereas 80% were incongment. The focus of the present review. howmer. is negative priming and. therefore, this point will be given no hirther scrutin!.
Reduced Stroop Interference - 49
Table 7
~Mean Response Times (in ms) and Percentage Error Rates to Name Colour ,as
a Function of Grouo r 1 , 2. or 3). From Besner (2000).
Group 1 Group 2 Gro~ip 3
Incongruent 753 3.4 723 3 .O 759 2.3
Control 660 2.0 68 J 2.9 758 2.9
Difference 9 3 1.4 39 0.1 1 0.6
Note: RT = response Times; %E = percentage of errors
Reduced Stroop Interference - 50
irrelevant words are being processed subsequent to colour naming (a sort of second-look
hypothesis following response). This was a necessary position for him to assume, given his
rejection of automatic word reading in this condition. Unfortunately, this is a post hoc argument
and is not consistent with the prevalent accounts of negative priming. My position is that the
presence of negative priming in the single letter coloured condition is expected if the word is
read automatically, and that this evidence is therefore actually inconsistent with Besner's overall
claim. Negative priming in the single letter coloured condition shows that the words in that
condition were being read, and quite strongly implies that they were being read automatically.
Had words been read subsequent to colour naming, there would be no reason to suppress them as
they would no longer interfere with the colour naming process already cornpleted for that trial.
Rationale for the Present Study
That negative priming is found when a single letter is coloured is the firsr piece of explicit
evidence that supports the notion that distractors are being read when a single letter is coloured.
Nonetheless. to further determine whet her distractors are being read, and thus whether the Stroop
effect can be elirninated. additional evidence is necessary. Consequently. 1 have chosen to use an
altemate method of detennining whether distractor words are being read when a single letter is
coloured in the Stroop task relative to the entire word being fully coloured.
The main focus of the present study will be an examination of memory for words that are
presented during Stroop t d s by providing participants with a number of words that are not the
colour words usually used. Following a Stroop-like task - using ordinary noncolour words as
distractors - participants will be presented with a surprise recognition test for these words. with
half of the items having appeared during the Stroop trials and half not having appeared during
Reduced Stroop Interference - 5 1
the Stroop trials. If participants are able to identiQ words which were presented to them with a
single letter coloured during Stroop trials at a level greater than chance, it will indicate the words
have in fact been read and understood. If performance on single letter coloured words is low (at
or around chance levels), however. the critical cornpanson will be between words that appeared
with a single letter coloured and words that appeared fully coloured. If recognition mernory for
fully coloured words is also low. then it would suggest that either the recognition task is not an
appropriate measure of whether distractor words are being read, or that there is no appreciable
difference in the manner in which participants process distractors appearing hlly coloured and
distractors appearing with a single letter coloured. If. however, recognition is high for hlly
coloured words but low for single letter coloured words, this would definitely be consistent with
the Besner et al. (1997) argument that colouring a single letter of a distractor word blocks
semantic processing by making the processing of these words different from that of hlly
coloured words.
Although the major focus of the present thesis is to determine whether irrelevant words are
read when a single letter is coloured dunng the Stroop task. there are additional issues that will
also be investigated. First, the possible influence of the position of the coloured letter has
already been outlined and will receive ample attention in the present research. Al1 experiments
have been designed in a manner such that useful comparisons can be made with regard to
response time and recognition rates as a function of coloured letter position. Second. regardless
of whether distractors are being read during the Stroop task. an additional issue has arisen: that
being the manner in which and the extent to which irrelevant words are processed when a single
letter is coloured relative to when al1 letters are coloured. Even if irrelevant words are always
read during the Stroop task, independent of colouring type, the single Ietter coloured
Reduced Stroop Interference - 52
manipulation may lead to differential processing of irrelevant words relative to that engaged by
fully coloured words. For example, a two-process explanation has been introduced to account
for the results of Besner et al. (1997) in which response times would rise due to an increase in
search time but coincidentally drop due to a decrease in Stroop interference, perhaps because the
irrelevant word becomes less word-like. Although it seems reasonable to speculate that two
processes may offset each other to influence response tirne when a single letter is coloured. it is
difficult to argue for this unless these processes are parsed apan and s h o w to influence
responding individually in the predicted manner. Thus. a number of aspects of the present
expenments will attempt to separate these mechanisms so that the manner in which single letter
coloured words are processed relative to fully coloured words can be determined.
The present study consists of four experiments. The fkst expenment is a replication of the
Besner et al. (1997) Expenment 2 with an iocreased emphasis on the position of the coloured
letter. It is assumed that Besner et al.'s (1997) basic pattern of results will replicate. given that
these results have already been independently replicated twice. The influence of the position of
the coloured letter is less readily predictable and remains an empincal question. This replication
will provide no information, however. as to the rnanner in which distractors are processed and
whether rhey are being read. Thus. Expenment 2a is the first explicit test in the thesis of whether
distractors are being read when a single letter is coloured during the Stroop task. A task similar
in nature to the Stroop task in the present Experiment 1 will be used, but noncolour words will
serve as the distractor items. Though these words are not supposed to be read. a recognition task
will test participant memory for the presented words. Particular interest will be given to those
words that appeared with a single letter coloured relative to words that appeared fully in coiour.
If single Ietter coloured words are recognized at a level equal to fully coloured words (and at a
Reduced Stroop Interference - 53
rate greater than chance). it would suggest that irrelevant words are read when a single letter is
coloured, contrary to the claims of Besner et al. (1997) but consistent with my interpretation of
the Besner (2000) negative priming data. It is predicted that single letter coloured words will be
remembered at a rate greater than chance and at a rate equal to fully coloured words. The
influence of the position of the coloured letter on both response time and recognition rate will
also be investigated in this experirnent. Again, no a priori predictions were made regarding any
expeaed pattern of positional results. only that letter position may be infiuential.
Regardless of the outcome of Experirnent 2a. there is still a need to investigate the manner in
which irrelevant words are processed when a singie letter is coloured relative to al1 letters.
Specifically, a two-process expianation has been introduced to account for the results of Besner
et al. ( 1 997). Thus. Experiments 2b and 3 served two functions: ( 1) to supplement the results of
the first two expenments in determining whether irrelevant words with a single letter coloured
are processed differently then irrelevant words with al1 letters coloured. and (2) to parse apan the
two processes that 1 have posited to account for the results of Besner et al. ( 1 997). In particular.
these experiments test the notion that colouring a single letter of an irrelevant word increases
participant response time relative to colouring al1 letters of an irrelevant words while
sirnultaneously reducing response time due to a decrease in interference associated with the
irrelevant word, resulting in a net offset between the two processes.
Experiment 2b was a simple word reading task in which some words appeared hlly coloured
whereas others appeared with a singie random ietter coloured. The expectation, in accordance
with the two-process account. was that words with a single letter coloured would take longer to
read than would words that appeared hilly coloured.
Finally. Experiment 3 was a Stroop-like task using rows of asterisks rather than irrelevant
Reduced Stroop Interference - 54
words as distractor items. Again it was expected that it would take participants longer to colour
name when a single asterisk was coloured relative to al1 asterisks being coloured. If this rise in
response time for single letter coloured displays is prevalent in both Expenments 2b and 3. it
would provide considerable support for the two-process account. It is difficult to determine
whether colounng a single letter reduces Stroop interference without experiencing this
corresponding increase in response time. Nonetheless, colouring a single letter has led to a nse
in response in al1 conditions except the colour word condition across three experiments (Besner
et al.3 colour nonwords; Marmurek's animal words. and MacLeod's rows of' X's) and it
therefore seems reasonable to posit that a decrease in colour word interference in the colour word
condition is responsible.
General ~Method
Apparatus and Materials
Each expenment in the present study was wntten in QuickBASIC and was adapted from the
same program that was used for MacLeod's (1999) independent replication of the Besner et al.
(1997) Experiment 2. An IBM-compatible 486 cornputer was used to display the stimuli on a
Ma_enavox 15" colour monitor and participants responded using either the keyboard
(Experiments 1 .2a and 3) or a microphone (Expenment 2b). dependent upon the experimental
requirements. When the experimental task was a colour-identification task (Experiments 1. 2a.
and 3)+ participants responded using one of four response keys (z, x, >, or ?) representing the
four colours (red. blue. yellow. and green. respectively). The response rnethod for the
recognition test in Experiment 2a and for the word reading task in Experiment 2b will be
outlined in the Apparatus and Materials sections of those experiments.
Reduced Stroop Interference - 55
A practice task was also incorporated into each experimental session that consisted of
displays of asterisks with either a single astensk or al1 astensks coloured. Participants indicated
display colours using the same four keys as previously outlined.
The stimuli used in Experiment 1 were the same colour words (red, blue. green. yellow) and
corresponding colour nonwords (ret, blat. grend. yenile) used by Besner et al. (1997). Ail colour
words and colour nonwords appeared in incongruent colours and lowercase type. to be consistent
with Besner et al. ( 1997), Marmurek (1999), and MacLeod ( 1999).
The stimulus set for Experiments 2a and 2b consisted of 160 noncolour English words (see
Appendix A). The selection procedure for these words will be fùrther detailed in the materials
section of those experiments. For Experiment 3. the stimulus set consisted of rows of asterisks.
between 3 and 6 asterisks in length. Ail stimuli in Expenments 2 and 3 appeared with either a
single character or with al1 characters coloured. In al1 experiments. there was an equal number of
fully coloured and single letter coloured trials. When only a single letter was coloured. each
letter position was represented in as equal a rnanner as possible.
Procedure
This section will detail the procedure for every colour naming task (Expenments 1. ?a. and
3 ) The procedures for the recognition task in Experiment 2a and for the word reading task in
Experiment 2b will be detailed in their respective Method sections. Al1 other experiments are
replications and extensions of Besner et a1.k (1997) Experiment 2.
Prior to testing, participants indicated their willingness to panicipate by filling out a consent
form that bnefly detailed the nature of the study (see Appendix B 1). Participants then sat
approximately 30 cm fiom the monitor. with a keyboard in front of them. To farnilianze
participants with the button pressing procedure that was to be used during the expenment, they
Reduced Stroop Interference - 56
initialy perfomed 72 tnak in which a row of asterisks at the center of the screen appeared either
fully in colour or with a single, randomly varying, asterisk coloured. Participants were instructed
to indicate the display colour of the row of astensks or the single asterisk by pressing the
corresponding button on the keyboard, as just outlined. This task allowed participants to Ieam
the button pressing procedure in the absence of distracting colour words and equivalent
nonwords. Following the familiarization task, participants took part in the actual expenment.
Participants were initially presented with wntten. on-screen instructions (see Appendices C
through F) which were supplemented by oral instructions pnor to the experiment. On each trial,
a single word, colour nonword. or row of asterisks was presented in the middle of the computer
screen. Each stimulus appeared either entirely in colour or with a single randorn character
coloured. Participants were instructed to ignore the irrelevant word or nonword and to indicate
the display colour of the entire item or single letter by pressing the conesponding button on the
keyboard as quickly and as accurately as possible. Immediately following a manual response.
the stimulus disappeared fiom the screen. Afier a penod of 500 ms. a row of asterisks appeared
on the screen to alert participants that another item would follow rnomentarily. The nea target
stimulus appeared after 500 ms. This warning was used in al1 experiments except Expeirment 3.
in whkh a row of dashes were used because the distractor items were rows of asterisks.
Each panicipant completed a set of practice trials followed by the actual experimental trials.
Al1 trials were randornized. with half of the trials being incongruent trials (colour words) and half
being neutral trials (colour nonwords). In addition. half of the trials had al1 letters coloured
whereas half had only a single Ietter coloured. In this latter case, the position of the single
coloured letter varied randomly, with each position being equally likely to be the critical
coloured letter. Upon completion of al1 experimental trials, participants were debnefed as to the
Reduced Stroop Interference - 57
purpose of the experiment and @ven their credit slip (see Appendix B2).
Experiment 1
This is a replication and extension of the Besner et al. (1997) Experiment 2. with the
additional goal of determining the effect of the position of a coloured letter relative to a fully
coloured word. The basic procedure for the experiment was exactly the same as in Besner et al.
(1997). and it was expected that the principal phenornenon they observed - the
decline/elimination in interference in the single letter coloured condition - would replicate. given
prior replications by Marmurek (1999) and MacLeod (1999). The new emphasis would be on
additional analyses camed out to determine the effect of the position of the coloured letter.
The three different potential patterns of results already outlined for coloured letter position are
shown in Figure 1. Basically. Stroop interference could increase or decrease as the participant
scans lefi to right. A decrease would be expected if Logan and Zbrodoff (19%) are correct in
positing that the first letter of an incongnient colour word is mostly responsible for Stroop
interference. On the other hand, an increase would be expected if interference increases as a
hnction of how much of the irrelevant word is scanned (e-g., if the individual is scanning lefi to
right. they will have seen more of the irrelevant word when the last letter is coloured relevant to
when the first letter is coloured). In accord with the findings of Regan (1978) and Logan and
Zbrodoff (1998), it was anticipated that colouring the first letter would lead to equal Stroop
interference in both the incongnient and control conditions, but the effect for the other letter
positions is less readily apparent.
Method
Participants. Thirty-five University of Toronto at Scarborough undergraduates, both male
and female, participated for course credit. Each participant had normal or corrected to normal
Reduced Stroop Interference - 58
vision as determined by self-report. Testing time for each participant was approximately 15
rninu tes.
Materials. The stimulus set used in the present expenment was the same colour words (red.
blue, green, yellow) and corresponding colour nonwords (ret. blat. grend, yenile) used by Besner
et al. (1997), together with the same four pint colours..
Procedure. The present expenment replicated, as closely as possible. Besner et al.3 ( 1997)
Experiment 2 and the basic procedure was outlined in the General Method section. Following
the initial practice session, participants compieted 192 colour-identification trials.
Results
Al1 analyses in the present experiment and in the following two expenments were performed
using SPSS. Response times were excluded from analysis for trials on which colour naming
errors were made. or when naming times were less than 300 ms or greater than 2000 ms. These
latter exclusions were also considered errors. but occurred very rarely.
Reduced Interference in the Single-letter-coloured Condition
One purpose of the present expenment was simply to replicate the pattem of results that was
reported in Besner et al. (1997). To examine the success of this goal. mean colour naming times
for incongrnent colour words and control colour nonwords. appearing both fully coloured or with
a single letter coloured. were obtained for each participant. Mean naming times. standard
deviations, and percentage errors are show for each of these conditions in Table 8. Besner et
al.'s (1 997) basic pattem of results was the reduction/elirnination of Stroop interference in the
single letter coloured condition. The present results replicated the reliable reduction but not the
elirnination in their pattem of data. When distractor words appeared fully coloured, it took
participants longer to colour name on incongruent trials relative to control trials, a difference of
Reduced Stroop Interference - 59
Table 8
Esperiment 1: Mean Response Times (in ms), Standrird Detiations. and Enor Ehtcs to
N m e Colour as a Function of Condition (AI1 Letters Coloured tvs. Single Letter Coloured).
Al1 Létters Coloured Single Lctter CoIourcd
Condition RT SD %E RT SD %E
Incongruent 729
ControI 684
D ifference 45
112 3.7 742 102 4.9
1 O4 4.0 720 1 Or) 4.2
8 0.3 22 2 0.7
Note: RT = response times; SD = standard deviation: Y& = perccntagc of mors
Reduced Stroop Interference - 60
16 ms. When distractor words appeared with a single letter coloured, however, this difference
reduced to 22 rns. Again, participants took longer to colour name when distractor words were
incongruent as opposed to control. This reduction in naming (or. more properly. identification)
response was mostly attributable to a rise in naming times in the control condition, also
consistent with Besner et al. 's ( 1997) pattern of results.
Although their basic pattern of results replicated. the present study did not obtain an
elimination of the Stroop effect: There were 22 ms of interference remaining when a single letter
was coloured relative to the entire distractor being coloured. A 2 X 2 within-participants
anaiysis of variance (ANOVA) was performed on the mean colour naming response times with
colour type (fully coloured or single letter coloured) and distractor type (incongruent colour
word or colour nonword) as the independent variables. There was a significant main effect of
colour type, (1, 34) = 14.68, MSe = 1367.03, g < .O0 1. and a significant main effect of
distractor type. F (1. 34) = 33.53. MSe = 1 184.83. g < .O 1. In addition. there was a significant
interaction between colour type and distractor type, F ( 1. 34) = 4.24, MSe = 1 1 16.12, EI < .05. A
summary table for the ANOVA appears as Appendix G.
Two planned comparisons firther corroborated that the present pattern of results was sirnilar
to the pattern obtained by Besner et al. ( 1997). There was no significant difference between
colour naming tirnes for incongruent colour words appearing fully coloured (730 ms) and
incongruent words appearing with a single-letter coloured (742 ms), ( 1. 34) = 1.84. MSe =
1367.03, p > . O 5 There was, however. a significant difference between colour naming times for
control items appeanng fully coloured (684 ms) and control items appearing with a single letter
coloured (720 ms), F (1. 34) = 16.59. MSe = 1367.03. g < .O 1. Two additional paired sarnple t-
tests demonstrated that there was a significant difference between the interference observed
Reduced Stroop Interference - 6 1
when al1 letters were coloured (46 ms) relative to a single letter (22 ms), [ (34) = 2.06, p < -05
and a significant difference between the interference observed when a single letter is coloured
and zero interference, 1 (34) = 3.52, g < .O 1. This finding is key as it demonstrates that Stroop
interference was still highiy prevalent when a single letter was coloured. contrary to the findings
of Besner et al. (1 997) and Besner and Stolz (1 999ah).
Mean error rate deviations as a function of distractor type and colour type can also be found
in Table 8 and mean error rates as a function of the position of the coloüred letter can be found in
Table 9. A 2 X 2 within participants ANOVA was performed on mean error percentages, again
with colour type and distractor type as the independent variables. There was no main effect of
distractor type nor was there a significant interaction of colour type and distractor type, both Es <
1. There was. however. a marginally significant main effect of colour type. F ( 1, 34) = 3.4 1,
MSe = 0.0005, e = .07, with more errors occurring for words with a single letter coloured than
for fully coloured words (see Appendix H). This demonstrates the absence of any speed-
accuracy tradeoff between the critical colour type conditions.
To further examine the significant effect of colour type, two planned cornparisons were
conducted. The first demonstrated no overall effect of colour type on control items. F < 1. In
contrast, the second demonstrated a significant effect of colour type on incongruent colour
words, (1 , 34) = 10.08, MSe = 0.0005, g < .O 1, with more errors occumng when a single letter
was coloured relative to al1 leners being coloured.
Position of the Coloured Letter
Due to the present interest in the position of the coloured letter (namely. is interference a
function of letter position with more interference occumng for coloured letters appearing earlier
in words versus coloured later?), several analyses were camed out to examine this effect in
Reduced Stroop Interference - 62
Table 9:
E~mriment 1 : Mean Response Times (in ms). Standard Deviations and Error Rates
to Identifv Colour as a Function of Letter Position (Incongruent Colour Words vs.
Convol Items) in the Single Letter Coloured Condition.
incongruent Words Control Items
Coloured Letter Position RT SD %E RT SD %E - . .-
1 745 97 6.4 743 179 6.7
2 742 135 4.2 73 1 120 4.9
3 744 115 5.8 692 83 1.8
4 751 146 3 . 3 719 140 4.1
5 732 170 4.6 723 145 3.4
6 709 188 1.4 710 164 0.0
Note: RT = response Urnes: SD = standrird de~iation; %E = percentage of mors
Reduced Stroop Interference - 63
greater detail. The critical analyses concerned the response time data and the outcome was
absolutely clear.
Two one-way within-participants ANOVAs demonstrated no main effect of the position of a
coloured letter on response times for control items. E (5. 170) = 1-36. MSe = 8062.73. p = 24. or
for incongrnent items, 4 (5, 170) = 0.71, MSe = 1 1050.72, p = -62 (see Appendices 11 and 12).
Error rates were also examined, and ANOVA tables for these analyses can be found in
Appendices J 1 through J8. Due to the large number of compansons (most of them
nonsignificant), they will not be reported in depth. There are, however, a few interesting
compansons worth noting.
Two one-way within participants ANOVAs were performed to examine the effect of the
position of the coloured letter on error rates for incongrnent colour words and colour nonwords.
These analyses demonstrated no effect of the position of the coloured letter for incongruent
colour words. F (5, 170) = 1.58. MSe = 0.01. g = .30 (see Appendix J 1). but a significant effect
for colour nonwords, E (5. 170) = 5.09. MSe = 0.004. e < .O1 (see Appendix J2). It should be
noted that the highest error rates were recorded when the first letter was coloured and the next
highest error rates were recorded when the second letter was coloured (see Table 9).
There were no significant differences in error rates between incongruent colour words and
colour nonwords when either the first letter or the second letter were coloured, both Es < 1.
There were, however, significant differences between incongruent colour words and colour
nonwords when the third, founh, or fifih letters were coloured (see Appendices J3 through J8),
with a greater number of errors occumng for words. This is to be expected given that the third
letter of each colour nonword is the position where these words are first confirmed not to be
colour words. This difference did not hold, however, when the sixth letter of colour words and
Reduced Stroop Interference - 64
control items appeared in colour (i.e.. the word YELLOW or the nonword YENILE). This could
simply be due to the low proportion of trials with the sixth letter coloured in the present
experiment (less than 5% of experimental trials).
Due to the significant effect of the position of the coloured letter on colour nonwords. a
Tukey HSD was performed to compare the difference in error rates as a function of the position
of the coloured Ietter in control items. Of particular interest to the present experiment was the
finding that there was only a slight difference in error rates between controls with the first letter
coloured and those with the second letter coloured (with more errors occumng for items with the
first letter coloured). There were. however, substantially more errors when the tirst letter was
coloured relative to al1 other coloured positions.
Discussion
The results of Experiment 1 replicated one of the key elements of the basic pattern of results
from Besner et al. (1997). with reduced interference for single-letter-coloured as opposed to fùlly
coloured words. Unlike in Besner et al. (1997). however. in this experirnent interference was not
eliminated when only a single letter was presented in colour. Although 24 ms of Stroop
interference was removed when participants responded to single letter coloured words relative to
M y coloured words (which is almost the exact average of Stroop interference eliminated across
the Besner et al.. 1997. MacLeod. 1999. and Marmurek. 1999. studies), a reliable 22 rns of
Stroop interference remained. So even in the Besner et al. (1 997) set of conditions - manual
responding and colour nonword controls - the outcome is not always elimination of interference
in the single letter coloured condition (see also Marmurek, 1999).
The safest conclusion is that colouring only a single letter reduces interference by 20-30 ms.
an interesting result certainly deserving explanation. Again, however. the majority of the
Reduced Stroop Interference - 65
reduction in Stroop interference can be attnbuted to a nse in control response times rather than to
a decrease in incongruent response times. This was also the case in the Marmurek (1999) and
MacLeod (1999) replications and extensions of the Besner et al. (1997) study. as indeed it was in
the Besner et al. series of studies. Thus. the present results corrorborate the results of Marrnurek
(1999) and MacLeod (1999) in demonstrating that the Stroop effea is reduced but not elirninated
by colouring a single letter of a distractor word. Rather it appears that a number of the
methodological choices that were made by Besner et al. (1997) sometimes lead to apparent
elirnination of Stroop interference.
Are Colour Nonwords a Suitable Control Condition?
A secondary senes of analyses provide sorne suppon for the argument that the Besner et al.
(1997) controls may be inappropriate. Earlier. 1 argued that using the colour nonwords (e.g..
RET) as controls rnay be questionable given that Stroop interference has been known to occur
for the first letter or letters of an incongruent colour word. A series of one-way within-
participants ANOVAs was conducted to compare response times for letter positions in control
items relative to incongruent colour words. There was no significant difference when the first or
second letter was coloured. This pattern changed, however, when either the third or fourth letter
was coloured. When the third letter was coloured. naming times were faster for control
distractors by 52 ms. M e n the founh letter was coloured, narning times were again faster in the
control condition, though this difference only approached. and did not achieve. conventional
levels of signîficance (p = .07; see Appendices K I through K6 for ANOVA summary tables and
Table 9 for means and standard deviations).
This is the pattern of results that would be expected if the first two letters of control items
(and thus, the control condition itself) elicit Stroop interference. No significant difference.
Reduced Stroop Interference - 66
however, was recorded between narning times for control and colour words when the fifth and
sixth letters were coloured, thus making this pattern of results difficult to interpret. It could be
that there are an insufficient number of trials where the fifih or sixth letter is coloured (only in
GREEN, GREND, YELLOW, and YENLE) to make any valid inferences regarding these
positions. The design of the present experiment led to a low proportion of such trials given that
each position was coloured equally ofien for each word length, and that five and six letter words
with a single letter coloured accounted for a mere 25% of the experimental data across al1 letter
conditions (and therefore, about 5% across al1 tnals).
More on Positional Effects
There was little efFect of letter position in the present study. None of the three foreseeable
patterns of results were even remotely evident. This may suggest that participants either fail to
form a strategy when performing the Stroop task, or that they form a strategy that is less intuitive
than those previously outlined. One such possibility would be a twist on the predicted pattern of
results that was outlined in the two-process explanation for the Besner et al. ( 1997) results.
Here. 1 suggested that panicipants rnight scan fiom left to right when each new word is
encountered such that the first letter of distractor words would provide the desired response on
more than 50 per cent of tnals (Le., al1 fully coloured trials plus some single letter coloured
trials). The response time results for individual letter positions in Experiment I do not support
this possibility.
Alternatively, participants may remain fixated on the position of the screen where the last
single coloured letter appeared and not engage in additional search until another single letter
coloured item appears (with the coloured letter likeiy to be in a diferent position than that in the
previous single letter coloured item). This seems reasonable, as the participant no longer decides
Reduced Stroop Interference - 67
to retum to the lefi side of the screen to orient to the next target, rather they remain fixated on the
position where they ended up on the previous trial. For example, if the participant encountered a
four-letter word with the third letter coloured, they would search for that coloured letter and
respond. If the following word appeared fully in colour. or was another four letter word (or, to a
slightly lesser extent, a three or five letter word) with the third letter coloured. then the
participant would be able to respond without engaging in any additional search for the coloured
letter. This response strategy is probably easy for the participant to engage in. but unfonunately
does not lend itself to a predictable pattern of results, given that the position of the coloured letter
and the order of presentation of trials is cornpletely randomized4. To preface the following three
expenments, positional analyses were also conducted. but in no case was any interpretable
pattern observed. I will, therefore. limit the discussion of positional analyses hencefonh.
The Importance of Errors
1 have argued that the Besner et al. (1 997) controls may be inappropriate because Stroop
interference may be occumng for these items. due panicularly to the first two letters. This
result was supponed by the previously reviewed response time data and is fùrther corroborated
by the present error rate data. First, there was no overall difference in error rates between colour
words and colour nonwords. Assuming that errors are the result of improperly responding to the
distractor. one should expect fewer errors in the control condition if the controls are free of
Stroop interference. This is not the case here, suggesting that the colour nonword controls do
elicit Stroop interference.
4~nother way of thinking of the dinerence behveen hilly colowed words and words tkiiih a single lener coloured is that the latter contain a greater number of characten which m e elicit a response. For esample. relative to a sis letter word nith one letter coloured a fully coloured sis letter word has six times as man? chancten which the individual can respond to (if the word is king btoken dowvn into individuai letter components). A stimulus sampfing theory (e-g. Estes. Bjork. & Skaar. 1974; Estes. Mlrneyer. & Reder. 1976) might prove usefbi in thinking about how these letters are processed,
Reduced Stroop Interference - 68
This interpretation was further corroborated by the positional analyses that were camed out
on error rates. When either the first or second letter of a control item appeared in colour, there
was no difference in error rates between incongruent colour words and colour nonwords. When
the third letter was coloured. however, substantially more errors were made when the distractor
was a word rather than a control. According to the Regan (1978) and Logan and Zbrodoff
(1998) positional theories, no difference should be observed between the first two letters of
colour words and the Besner et al. (1997) colour nonwords. This was indeed the case.
Interestingly, for both incongment colour words and incongment colour nonwords. most errors
were made when either the first or second letter was coloured. consistent with the argument that
the first one or two letters of incongrnent colour words may provide the bulk of Stroop
interference. A sirniiar pattern of results emerged in the positional comparisons. There was a
significant (or marginally significant) diference in error rate when the first letter was coloured
relative to when any letter other than the second letter was coloured. I î is also of interest to note
that significantly more errors were made by participants when inconpent colour words
appeared with one letter coloured relative to fùlly coloured. This pattem of errors is highly
inconsistent with the Besner et al. (1997) argument that colouring a single letter prevents the
semantic processing of an irrelevant word. If this were the case, then one would expect fewer
errors when a single letter is coloured relative to the entire word being coloured. assuming ihat
errors are the result of an inappropnate (or uncontrolled) response to the irrelevant word?
Despite the fact that I have argued against Besner et al.3 (1997) explanation for their results.
it is unquestionable that these researchers have still obtained an interesting pattem that deserves
%bis argument seems teasonable b u s e there is no dinerence in enor rates as a fùnction of colouring hpe in the e~periment that follows. which consists of a merent English language word on eveq trial. These words are l e s likely to cause interference relative to incongruent colow words.
further attention. In particular, the reduction of Stroop interference. and the corresponding rise
Reduced Stroop Interference - 69
in control condition response times rather than decline in incongment condition response times.
both seem to be highly replicable. The following experiments further investigate the manner in
which Stroop interference is reduced and the differential processing that may occur for single
letter coloured items relative to fully coloured items. Experiment 2a will investigate recognition
memory for words that appeared during a Stroop task versus words that did not appear
Experiment t a
The results of Experiment 1 partially replicated the basic pattern of results from Besner et al.
(1997). Expenment 2. Looking solely at response time data colouring a single letter reduced the
Stroop effect by 23 rns - a result which matches the average reduction in Stroop size across
conditions in the MacLeod (1999) study. This reduction did not. however, result in elimination
of the Stroop effect. Thus. including the present Experiment 1. numerous studies have now been
conducted which have demonstrated a reduction in Stroop interference as a function of colouring
a single letter (Marmurek, 1999; MacLeod. 1999). but not an entire elimination of this
interference. This would suggest that rnerely colounng a single leiter does not fully eliminate
Stroop interference, contrary to the claim of Besner et al. ( 1997; Besner & Stolz 1999ah). As
has been previously stated. however, these studies al1 must rely on response time data with no
explicit evidence to suggest that colouring a single letter prevents participants from reading a
distractor word or, at the very Ieast, that distractor words are processed differently. Thus.
Experiment 2a was designed as a more explicit test of whether distractor words were being read
dunng Stroop trials.
The first phase of Expenment 2a consisted of a Stroop-like colour naming task in which each
distractor was a different noncolour word. Naming the colours of these noncolour words was
treated as a kind of study phase. so that memory for them could be tested following the Stroop
Reduced Stroop Interference - 70
task with a surprise recognition test. It would not have been wonhwhile to test memory for
target words in the first study because the same eight items (colour words and colour nonwords)
were presented numerous times and. therefore, would be very easy to identiQ. By presenting
each target word only once, the recognition task here provides a more powerfil test of whether
words are being read in the single letter coloured condition, contrary to the explicit instructions
not to read them. If something about colouring a single lerter causes a word to be processed in a
less wordlike manner. it would be expected on a levels of processing basis (cf Craik & Lockhart.
1972) that fully coloured words should be recognized more quickly and more accurately than
single letter coloured words. This would also seem to be what Besner et al. ( 1 997) would
predict, given their argument that words are not automatically read and that semantic analysis is
blocked in the single letter coloured condition. If. however. single letter coloured words are in
fact encoded as words to the same extent as hlly coloured words. then a different recognition
pattern is expected: Single- letter-coloured words should stiil be recognized at a rate greater than
baseline (Le., the false alarm rate of incorrectly recognizing words that did not appear during the
Stroop task), and indeed should be recognized just as well as fully coloured words.
Both Marmurek ( 1999) and MacLeod (1999) obtained a Stroop effect for words appearing
with a single letter coloured in their studies pattemed after Besner et al. (1997) when they used
vocal as opposed to manual responses. The present Expenment 1 also obtained Stroop
interference. albeit reduced. when a single letter of an irrelevant word was coloured. Clearly, in
these cases. the target word is being read despite explicit instructions not to read it. It is
therefore predicted that the recognition memory test will indicate that words appearing with a
single letter coloured are in fact being read. If so. this would indicate that automatic reading is
not elirninated simply by colouring a single letter of an irrelevant word and that a diKerent
Reduced Stroop Interference - 7 1
explanation is needed for the results of Besner et a1.k (1997) response latency data. Two
possible explanations regarding Besner et a h (1997) methodology that rnay have influenced the
data have already been outlined (manual response, unusual control stimuli) but surely other
viable explanations exist. If, however, recognition for words appearing with a single coloured
lener is poor relative to that for words appearing fblly coloured, this would be consistent with
Besner et a1.k (1997) daim that the Stroop effect can be eliminated in certain situations by
colouring a single letter, which defeats "automatic" reading and thereby leads to differential
encoding in the whole word and single letter coloured conditions.
Nonword control stimuli were eliminated from this expenment because the object was to
determine whether participants have read and understood the words that they were to ignore.
Even if nonwords were read, the panicipant would be unlikely to attach any meaning to these
stimuli or to be able to rernember them and. therefore. they are not appropriate for study. In
addition to accuracy. response latency was measured on the recognition test to compare times for
words appearing with a single letter coloured relative to words appearing fully coloured. As with
the first experirnent, the position of the single coloured letter vaned.
There is a possibility that recognition may be dependent upon the position of the coloured
letter. though there is no existing evidence to suggest this. If. for exarnple, colounng a single
letter causes a word to be processed in a less wordlike manner, then slower recognition times
might be observed for words that appeared with a single letter coloured relative to words that
appeared fully coloured. The influence of the position of a coloured letter on recognition
response cimes remains an empincal question. Thus, recognition memory as a function of lener
position was also investigated in the present experiment. Though the focus of interest in the
present expenment was recognition as a function of colour type, recognition as a function of
Reduced Stroop Interference - 72
letter position and response time was also considered.
Method
Participants. Thirty-eight University of Toronto at Scarborough undergraduates. both male
and fernale, participated for course credit. Al1 participants had normal or corrected to normal
vision (as determined by self report) and none of the participants had participated in the first
experiment. Testing time for each participant was approximately 15 minutes.
Materials. The materials used for the experiment were 160 noncolour common English
words. These noncolour words. ranging from three to six letters in length, were matched with
regard to word length and frequency using the Thorndike and Lorge (1944) noms. Of these 160
words. 40 were generated for each individual colour-word length (Le.. 40 three letter words. 40
four Ietter words, etc.). None of the 160 words began with the letters 7." "b." "y," or "g" to
avoid the potential problern that Besner et al. ( 1997) may have experienced with their controis.
There is a chance that a minimum of Stroop interference could occur with these noncolour words
seeing as Stroop interference has been reported for other English language words and not just the
colour words which are traditionally used in Stroop studies (Klein. 1964; see MacLeod, 199 1 ).
Such interference, however, is inconsequential to the present study as the purpose will simply be
to determine whether distractors are being read under letter search conditions. Nonetheless,
response time data will be analyzed to determine whether the obtained pattern of results mirrors
the pattern obtained by Besner et al. ( 1997).
These 160 words were divided into two equal lists of 80 words for use in the present
expenment, and in Expenment 2b. Rather than creating random lists of 80 words for each
participant. two permanent list randomizations were created and used randornly for Experiments
2a and 2b. The two lists were created because of concems emanating from pilot testing in which
Reduced Stroop Interference - 73
it was detennined that a number of words fiom the list of 160 shared some similanties (e.g..
iconic representation, sirnilar phonetics). Thus, there was cause for concem that some words
might provide complications for the participant during the recognition phase of the present
expenment. For example, if the participant saw the word "fog" during the Stroop-like colour
naming study task they could mistake it for "dog" or "log" during the recognition task. Thus,
the two lists of 80 were constnicted to ensure that such confusions would be kept to a minimum
(e.g.. the best attempt was made to keep rhyming words or words with very similar iconic
representations on opposite lists). The order of presentation of the two lists was a function of
participant number, with odd nurnbered participants seeing List 1 in Experiment 2a and List 2 in
Experiment 2b. whereas even numbered participants saw the sarne lists in the opposite order.
This was done to ensure that the obtained results were not confounded by the order of
presentation of lists.
Unlike the first expenment, words could appear in any of the four expenmental colours. This
was deemed unproblematic given that colour words and colour nonwords were not used in the
present experirnents and that there should be no inherent connection between stimulus length and
colour word length. This was also the procedure used for Experiments 2b and 3. in which al1
distractors could appear in any colour.
Procedure. Though the stimuli were different. the basic procedure of the study phase of this
expenment was similar to Besner et a1.k (1997) Experiment 2 and to the present Experiment 1 .
Although there were nearly 192 experimental trials in the first experiment (in accordance with
Besner et al., Mannurek, and MacLeod), the number of trials in this experiment wase decreased.
Because a greater number of different words were used here (a different noncolour word on each
triai). it would be unreasonabie to present participants with nearly 150 words and expect them to
Reduced S troop Interference - 74
remember many of them. In fact, pilot data suggested that presenting participants with even 64
words to remember was too great a load: Recognition performance did not exceed chance for
either single letter coloured or fully coloured words. Thus after the initial practice phase.
participants received 32 expenmental trials. Due to the small number of trials, it was impossible
to ensure that al1 letter positions would be equally represented on trials in which a single random
letter was coloured. This was not deemed problematic given that the results of the first
experiment, coupled with the pilot data for the present experiment, demonstrated that there were
no interesting effects of the position of the coloured letter.
Every participant had an experimental set of 64 words randomly drawn from the original list
of 80 words, with 32 of these words acting as colour naming study trials and recognition test
targets, and 32 acting as distractors on the recognition test that followed. Upon completion of al1
32 colour naming study trials, participants took pan in a surprise recognition test consisting of 64
triais. Half of the trials were made up of the words that appeared during the Stroop task (16 fully
coloured. 16 single letter coloured) and the other 32 were distractors. selected randomly fiom the
original list of 80 words. Each word appeared in white type on a black background. The order
of presentation of studied and distractor words was again randomized. Panicipants were
instructed that they were now to identifi the words that they had seen during the Stroop task and
to reject the words that they had not seen, taking as much time as necessary to complete this task.
On each trial, a single word appeared in the middle of the computer screen. Participants
responded to each word by pressing either the "P' button if they believed that the word appeared
during the Stroop task or the "z" button if they believed that the word was not presented during
the Stroop task. Hits, errors, and response latencies were recorded and analyzed for the
recognition test.
Reduced Stroop Interference - 75
Resuits and Discussion
Of the 38 participants that were tested, the data of four participants were excluded from final
analysis. Three of these participants were disqualified for failing to follow instructions during
the recognition test. Each of these three failed even to examine the words presented to them and
indicated that they did not think they had seen over 90% of the words. responding at a very rapid
speed. Dunng debriefing, two of the three participants admitted that they had completely
guessed during the recognition test and did not think there was any chance they had read the
words during the Stroop task. Thus. they did not even try during the recognition task. One
additional panicipant rnisunderstood the directions during the recognition task and was under the
mistaken impression that every word that was presented during this task had also appeared on the
Stroop task. This led her to indicate that she had seen nearly every word on the Stroop task
resulting in high hit rates for fully coloured and single letter coloured words. but a
correspondingly high false alam rate.
Because a large nurnber of analyses were conducted. the results will be divided into a number
of subsections. In addition, individual discussion sections will be presented following each
result section to avoid losing sight of important findings. The first set of analyses was perfiormed
on the initial phase of the present experiment. which consisted of the 32-item colour naming task
with a different English word presented on every trial.
Colour Naming Study Phase
Mean response times and error rates were calculated for each participant. Response time.
error rate, and standard deviation data for words as a function of colour type and position of the
coloured letter can be found in Tables 10 and 1 1.
A one-way within participants ANOVA was performed with colour type (fully coloured or
Reduced Stroop Interference - 76
Esperiment Za: Mean Remonse Times (in nis), Stnndxd Dc\iations. and Perccntaae Error Rates
to Name Colour as a Function of Condition (AH Letters Coloured vs. Single Letter Coloured).
RT SD %E
Fully Coloured
Single Letter Coloured
DifTerence
Note: RT = response times: SD = standard deviation: %E = pcrcentage of errors
Reduced Stroop Interference - 77
Table 1 1
Emrirnent 2a: Mean Remonse Times (in ms). Standxd Deviations, and Percentage Error Rates
to Name Colour as a Function of Letter Position in Single Letter Coloured Items at Studv.
Coloured Lener Position RT SD O/oE
1 733 137 7.1
7 756 157 4. J
3 695 190 1.5
4 754 180 2.9
5 800 257 1.5
6 693 197 0.0
Note: RT = response times: SD = standard de\riation; %E = percentage of crrors
Reduced Stroop Interference - 78
single lener coloured) as the independent variable and colour narning times as the dependent
variable. There was a main effect of colour type, F (1, 33) = 9.49. MSe = 2958.30, g < .01, with
participants taking longer to colour name words that appeared with a single letter coloured (743
rns) relative to words in which al1 Ietters were coloured (703 ms) (see Appendix L). A second
one-way ANOVA demonstrated a marginally significant effect of the position of the coloured
letter, E (1, 34) = 2.17. MSe = 25988.84, g = .O6 (see Appendix M). As in Experiment 1. there
was no meaningfii pattern of response time as a fùnction of coloured letter position and,
therefore. no further analyses were camed out in this regard.
As in Experirnent 1, a nurnber of planned analyses were camed out on error rates. A one-way
within participants ANOVA was performed with colour type as the independent variable and
error rate as the dependent variable. The analysis yielded no effect of colour type, < 1 (see
Appendix N). A second one-way within participants ANOVA. however, yielded a significant
effect of the position of the coloured letter on error rate. F (5. 165) = 2.37. MSe = 0.01. p = .O4
(see Appendix O). To investigate further this difference in error rates, a Tukey HSD was
performed to investigate al1 pairwise comparisons. As in the first experiment, there was only a
slight difference in error rates between controls with the first letter coloured and those with the
second letter coloured (with more errors O C C U ~ ~ ~ for items with the first letter coloured).
Participants, however, made significantly more errors when the first letter was coloured relative
to letters coloured later in the word. This is surprising because none of the distractor words in
the present experiment shared a first letter with the first Ietter of the incongruent colour words
that were used. Thus, this digerence could again be attributable to the higher proportion of trials
with the first letter coloured relative to trials with other lener positions coloured. The low
proportion of other Ietter trials makes it difficult to develop a cohesive explanation for these
Reduced Stroop Interference - 79
results.
Though the initial Stroop task was mostly used as the study phase for the surprise recognition
task to follow, the response time data add support to the two-process account. Recall that the
two-process account posits that colouring a single letter may reduce Stroop interference while
simultaneously increasing response time. In the present experiment, there should be little to no
interference attributable to distractors because colour words were not used. Even if the
distractors elicit a small amount of interference, however (as has been show to happen with
English language words; see Klein. 1964). this should have little systematic effect on response
tirne data because each trial contains a different random word with each word consequently
having an equal chance of eliciting Stroop interference. It is, therefore, safe to assume that the
present response time data Vary solely as a function of colouring type (single letter vs. whole
word). To that end. the response time data frorn the Stroop task support the notion that colouring
a single letter slows the colour naming response relative to words appearing fully coloured. Note
that this difference is in the 40 ms range, as is the difference in response time between colour
nonwords appearing fully coloured and colour nonwords appearing with a single letter coloured
in Besner et al. (1997). Experiment 2 (see Table 1). Thus, only incongruent colour words fail to
demonstrate an increase in response time when fully coloured words are compared to single
letter coloured words.
There is no reason to think that incongruent colour words are in any way immune to colouring
a single letter; thus. it is probable that an increase in response time occurs there as well. but is
offset by a coincident reduction in Stroop interference. This logic is consistent with the two-
process account proposed. Unfortunately. there is a fundamental problem in interpreting a
change in amount of interference (a difference score) when there is also a change in the control
Reduced Stroop Interference - 80
condition (against which the difference score is computed). In the Besner et al. case. they
emphasize the decrease in inteference fiom 30 ms to O ms as condition changes for fùlly
coloured to single letter
coloured. Yet at the same time. the control condition increased 30 ms From fully coloured to
single letter coloured. So there was essentially a perfect tradeoff Did interference decrease in
the incongment condition or did it increase in the control condition or was there just some
overall slowing in the single-letter coloured condition. perhaps due to the necessity to search for
the colour infomration? This complicates interpretation yet also forms the basis for the two-
process
explanation set out here. Further insight into this explanation will be gained when Experiments
7b and 3 are considered because they explicitly attempt to separate the two posited processes.
As in Experiment 1. there was no effect of colouring type on error rates. Error rates were
equal regardless of whether the entire word was coloured or a single letter of the word was
coloured. This result is not surprising if noncolour English words elicit hardly any Stroop
interference. It has been shown, however, that noncolour English words can elicit Stroop
interference, though not as much as incongment colour words (e.g. Klein, 1964: Dalrymple-
Alford, 1972). If distractors in the present experiment do elicit Stroop interference. then the
absence of an effect of colour type on error rates funher discredits Besner et a1.k (1997)
semantic disruption hypothesis. Under the semantic disruption hypothesis, error rates when a
single ietter is coloured should be reduced, if not eliminated, relative to error rates when the
entire word appears coloured. If this is the case. it would further corroborate the identical
finding from Experiment 1. where colounng a single letter of an incongruent colour word did not
reduce error rates relative to fùlly colouring incon_muent colour words. It is difficult to
Reduced Stroop Interference - 8 1
determine whether Stroop interference is present in the distractor words in Experiment 2% and
therefore this explanation is speculative.
As in the first experirnent. the data on the effect of the position of the coloured letter were
unirformative. Though there was a marginally significant effect of the position of the coloured
letter, none of the anticipated patterns of results were observed. Again, the altemate explanation
outlined in the discussion section of Experirnent 1 would seem to apply here: Participants are
trying to invent an efficient response strategy but it is certainly not strictly based on coloured
letter position.
There was, however, an unanticipated effect of the position of the coloured letter on error
rates, with higher error rates occumng for words with the first letter coloured relative to words
with later letters coloured. This result is surprising given that none of the distractors began with
the first letter of an incongruent colour word and. thus, cannot be accounted for by the ietter
position account derived from Regan (1978). Again. it may be that this result is an artifact of the
higher proportion of t d s with the first letter coloured relative to words with other letters
coloured. That aside, the important contribution of the Stroop task is in showing that colour
naming is slower for words containing a single coloured letter relative to words containing al1
letters coloured. This is entirely consistent with the two-process account because the Besner et
al. ( 1997) single letter coloured manipulation has led to an increase in naming response when
any distractor is used other than colour words (e.g. rows of X's, noncoIour words, colour
nonwords, animal names). Again. there is no reason to think that colour words are in some way
immune to this response time increase and therefore, it seems reasonabie to assume that a second
process is Ieading to a corresponding decrease in response time. The two-process account is
prornising in this regard.
Reduced Stroop Interference - 82
Recognition Test Phase
The key point of interest in Experiment 2a was the recognition rates for words appearing
during the initial colour narning study phase. If Besner et al. ( 1997) were correct in theorking
that colouring a single letter disrupts semantics, then words appearing fully coloured during the
Stroop task should be better recognized than words appeanng with a single letter coloured during
the Stroop task. IE however, colouring a single letter does not lead to differential processing of
the irrelevant words dunng colour naming relative to colouring the entire word, then there should
be no difference in recognition rates between fùlly coloured and single letter coloured words.
Mean hit rates and false alam rates were recorded for each participant. The false alarm rates
were used as the baseline recognition measure. No trials were eliminated due to response times
that were deemed too fast or too slow because participants were told to take as much time as they
needed for recognition. Mean recognition rates for each word type, expressed as the proponion
of "yes" responses, can be found in Table 12. Mean recognition rates as a function of the
position of the coloured letter can be found in Table 13.
A one-way within participants ANOVA was perfonned with word type (fully coloured, single
letter coloured, or new) as the independent variable and the probability of saying "yes" as the
dependent variable. There was a significant effect of word type, F (2. 66) = 53.68. MSe = 0.01.
p < .O 1 (see Appendix Q). To fùnher quali@ this main effect, three plamed comparisons were
conducted. These analyses demonstrated that the probability of a "yes" response to Mly
coloured words and single letter coloured words was significantly greater than to words that did
not appear dunng the Stroop task, F (1, 33) = 90.05, MSe = 0.0 1. p < .O 1 and F (1. 33) = 71 -79,
MSe = 0.0 1, p < .O 1, for fully coloured words and single letter coloured words, respectively. -
There was no difference. however. between hit rates for hlly coloured and single letter coloured
Reduced Stroop Interference - 83
Table 12
Esperiment Za: Mean Recognition Rates and Standard Deviritions for Hits (FiiIlv Coloured and Single
Letter Coloured Studied Words) and False Alarms (Words Not Presented During the Stroop Task).
PR("Yes") SD
Fully Colourcd 0.53 O . 17
Single Letter Coloured O. 50 0. 18
Not Presented 0.25 O. 13
Note: PR("Yes") = Probability of a "Yes" Response (Hit for a Studied Word: False Alarms for an Unstudied Word): SD = Standard Dwiation
Reduced Stroop Interference - 84
Table 13
Eweriment 2a: Mean Recognition Mes and Standard Deviations for Comctlv Rccomized
Words (in the Single Lettcr Coloured Condition) as a Function of Coloured Letter Position
Coloured Letter Position PR("Yes") SD
Note: PR("YesV') = Probability of a "Yes" Response (Hit for a Studied Word: False Alarms for an Unstudied Word): SD = Standard Deviation
Reduced Stroop Interference - 85
words, (1, 33) = 1.10, MSe = 0.01, g = .3 1.
As with the previous experiments, positional analyses were conducted in the present
experiment. This was accomplished by examining recognition rates as a function of coloured
lener position for words that appeared during the Stroop task. As in the two previous
experiments. there was no interesting effect of the position of the coloured letter, nor was there a
significant difference in recognition rate as a function of letter position, F (5, 165) = 1.04.
MSe = 0.12, = .40 (see Appendix R2). Tentatively, these results seem to discount the Besner et
al. (1997) argument that colouring a single letter leads to a disruption of semantic processing (or
even different ial processing).
The major point of interest in the present study was recognition rates for previously presented
distractor words. Recall that Besner et al. ( 1 997) proposed that colouring a single letter of a
distractor word tumed the colour naming task into a letter search task thus disrupting semantic
processing of the irrelevant colour word. In essence, Besner et al. (1997) argued that colouring a
single letter of a word causes that word to be processed in a less wordlike manner. The basis of
this argument was formed solely on response time data, however, in the absence of any esplicit
proof that the irrelevant words were not beinç read. Thus, the present recognition test was
designed to provide a more explicit test of how distractors are processed.
The results of the recognition test are inconsistent with the daim that colouring a single letter
disnipts semantics. There was no difference in hit rates between words that had appeared fully
coloured during the Stroop task and words that had appeared with a single letter coloured dunng
the Stroop task (53% and 50% for fully coloured and single letter coloured words. respectively).
Both of these word types, however. were correctly recognized at a much greater rate than the
false alarm rate for unstudied distractor words (25%). Had colouhg a single letter disrupted
Reduced Stroop Interference - 86
semantic processing. then it would be expected that recognition rates for such words would be
closer to the 25% false alarm baseline than to the 53% hit rate for studied targets. Clearly. this is
not the case.
Of course. it could be argued that recognition processes are not solely based on semantic
processing, and this is quite correct. Thus, the 25% baseline I am using may be a bit low. The
key issue in this experiment was whether single letter coloured words would be recognized at a
rate equivalent to fully coloured words, and this was indeed the case. Besner et a1.k (1997)
semantic blocking argument applies only to single letter word. not fully coloured words. That
recognition rates are equal for these two word types is indicative of some level of processing
above what has been predicted by Besner et al. (1997). even if it is possible that other factors
influence recognition rates. Though it could also be argued that recognition rates are still
relatively low for words that appeared during the Stroop task. they are being correctly recognized
considerably better than distractors are being incorrectly recognized. The low recognition rates
rnay simply be a function of the size of the stimulus set and their limited indirect. which may
make it difficult for participants to remember a greater proportion of words. Nonetheless. the
fact that fully coloured words were not systematically recognized at a rate greater than single
letter coloured words is encouraging for the present argument.
The relatively low recognition rate for words that appeared dunng the Stroop task is actually
not surpnsing in the face of past research. Szyrnanski and MacLeod (1 996) compared
recognition memory for words that were explicitly read to that for words that appeared as
distractors during a colour naming task and found that explicitly read words were recognized at a
greater rate than implicitly processed distractor words. When an implicit repetition priming
lexical decision task was presented to participants, however, explicitly read and implicitly read
Reduced Stroop Interference - 87
words showed equal levels of priming. Thus it could be the implicit nature of the present Stroop
study task that led to recognition rates of only 50%, but these words undoubtedly are being read.
One additional way to test this would be to give participants an initial Stroop task (identical in
nature to the Stroop task in the present experirnent) and follow it up with an implicit task such as
the lexical decision one used by Szymanski and MacLeod (1996) or the reading one used by
MacDonald and MacLeod (1 998). Identical performance for hlly coloured and single letter
coloured words on an implicit test would Further corroborate the present results in demonstrating
that colounng a single letter does not necessarily lead to a disruption in automatic processing.
Once again, the effect of the position of the coloured letter was investigated in the present
analyses and no interesting effect of letter position was found on recognition rates. Panicipants
were equally likely to recognize single letter coloured distractor words independent of the letter
that had appeared coloured.
Recognition Latency
Though no explicit predictions were made concerning recognition latency, a number of
analyses were performed in this regard. This was done for several reasons. First, in normal
recognition. it is generally expected that participants will respond to words that they have seen
faster than to words that they have not seen (Reisberg, 1997). In the present experirnent.
however, words were presented in a more irnplicit manner and, therefore, it seemed worthwhile
to determine whether this pattern would hold. Second. it might be expected that participants who
are slower on the initial Stroop task would have better recognition for distractor words because
they are exposed to these distractor words for longer than participants who are faster on the
initial Stroop task. Finally. these analyses were perforrned to investigate the pattern of
recognition response tirnes as a function of the position of the coloured letter during the Stroop
Reduced Stroop Interference - 88
phase. Mean response times and standard deviations for each word type and as a function of
coloured letter position are presented in Tables 14 and 15. respectively. Collapsed mean
response times for words that appeared during the Stroop task and words that did not appear
during the Stroop task, independent of correctness, can be found in Table 16.
To investigate whether participants would respond more quickly to words they had seen
during the Stroop task relative to words that they did not see during the Stroop task, a number of
ANOVAs were conducted that paralleled the recognition accuracy analyses from the preceding
section. Thus, a one way within participants ANOVA was performed to compare response times
for fully coloured hits (correct "yes" responses), single letter coloured hits, and unstudied false
alarms (incorrect "yes" responses). This analysis yielded no effect of previous exposure to
words on response time, F (2. 66) = 1.45. MSe = 1404 12.3, p = .24 (see Appendix S 1 ). A fùnher
analysis performed on recognition response times as a function of coloured letter position also
yielded no effect of letter position, F ( 5 , 165) = 1.2 1, MSe = 274557.7. p = 0.3 1 (see Appendix
S2). The expected pattern of response was observed. however. in the sense that participants were
faster to correctly accept words that had appeared dunng the colour naming study task (answer
"Yes") than to incorrectly accept nonpresented distractor words. Panicipants were also slower to
incorrectly reject words that appeared dunng the colour naming study task than to correctly
reject words that did not appear during study (see Table 14). The failure to reach statistical
significance may simply be due to the implicit nature of the present task. When participants
explicitly study words for later recognitioa they are thought to practice them in the interim and
therefore. have more experience with these words when they are to be recognized. In the present
experiment. however, participants were oniy implicitly exposed to words by unintentional
reading of distractors and it is extremely uniikely that these words were rehearsed in the interirn
Reduced Stroop Interference - 89
given that participants were
Table 14:
Esueriment 2a: Mean Response Times and Standard Dcviations for Words Auuearinq
Durine. the Recognition Task as a Function of Response Tvpc (Yes or No) and Word Tvpe
jFu1lv Coloured, Single Letter Coloured. and Not Presented).
Response Type
Ycs No
Full! Coloured 1189 493 1397 669 Single Letter Coloured 1214 572 1370 65 1
Not Presented 1342 556 1273 500
Note: RT = response times; SD = standard detiation
Reduced Stroop Interference - 90
Table 15
EsPenment 2a: Mean Remonse Times and Standard Deviations for Conectlv Recognized
Words (in the Single Letter Coioured Condition) as a Function of Letter Position.
Coloured Letter Position RT SD
6 1130 413
Note: RT = response cimes; SD = standard daiation
Reduced Stroop Interference - 9 1
Table 16:
E~wriment Za: Mean Responsc Times and Standard Dcviations (on the Recognition Taskl
Collapsed Across Conditions for Words That Appeared Durine: the Stroop Task (Prcsented)
and Words That Did Not Appear During The Stroop Task (Not Presented).
RT SD
Presented
Not Presented
DLBerence
Note: RT = Response Times: SD = Standard Deviation
Reduced Stroop Interference - 92
unaware that recognition test would follow. As in previous analyses, there was no effect of the
position of the coloured letter at study on recognition response times.
To investigate the possibility that participants who were relatively slow during colour naming
would have greater recognition memory for distractors due to increased exposure time - a kind
of "total time" of study hypothesis (cf'. Cooper & Pantle, 1967) - participants were divided into
two groups of 17 via a median split on speed of response. Recognition rates were then çenerated
for participants who were fast vs. slow overall, fast vs. slow on fully coloured words. and fast vs.
slow on single-letter coloured words. Three one-way independent samples t-tests indicated that
there was no difference in recognition rates between participants who were fast or slow in colour
narning for fully coloured words. single letter coloured words, or overall responses. al1 1s < 1 . In
retrospect. thiç is not a shocking result as recognition is generally dependent upon the manner in
which words are processed rather than on their duration of exposure (cf Craik & Lockhart,
1972). Slower participants did not necessanly engage in any extra processing of irrelevant
words relative to faster participants and, therefore. the observed equivalence in response rates is
not surprising
Finally, the present experiment investigated recognition response time for correct responses
as a function of the position of the coloured Ietter dut-ing the Stroop study phase. Mean response
times and standard deviations are presented in Table 17. It should be noted that not every
participant is represented at every letter position because some participants failed to provide any
correct responses for certain Ietter positions. In these cases. the mean of al1 participants for that
letter position was used. A one-way within participants ANOVA demonstrated no significant
difference in response time as a function of letter position, F (5, 165) = 1.2 1 MSe = 332588.7,
Reduced Stroop Interference - 93
Table 17:
Esperiment 2a: Mean Res~onse Times and Standard Deviations for Correctlv Recomizcd
Words (Single Letter CoIoured) as a Function of Letter Position.
Coloured Letter Position RT SD
1 1185 40 1
2 1205 977
3 13 82 50 4
4 125 4 544
5 1108 428
6 1130 4 13
Note: RT = response times; SD = standard de~iation
Reduced Stroop Interference - 94
e = -3 1 (see Appendix T). At this point. it seems unnecessary to perform any positional analyses
in later experiments. Nonetheless, 1 will continue with these analyses as they have been planned.
in case a meaningfùl pattern of results should anse in Iater experiments. This is a possibility
given that Experiments 2b and 3 are of a slightly different nature than the present experiment and
Expenment 1.
Due to the relatively undenvhelming nature of the response time results in Experiment Za, it
would be undesirable to terminate the present discussion without returning to the most important
findings from this experiment. First. there was no difference in recognition rates between words
that appeared filly coloured during an initiai Stroop task and words that appeared with a single
letter coloured during the same task. Both of these word types. however, were recognized at a
rate far greater than baseline. This finding casts serious doubt on the Besner et al. (1997) daim
that coiouring a single letter of an irrelevant word dismpts processing of that word and that it is
this that is responsible for the elimination of the Stroop effect. Clearly. single letter coloured
words are being read by participants. and apparently to the same extent as fully coloured words.
despite explicit instructions to the contrary. This is at least consistent with the idea that even in
the single letter coloured condition words are read automatically. Consequently, an altemate
expianation is needed for the results of Besner et al. (1997).
Data from the present colour naming task support the previously outlined two-process
explanation, with participants taking 40 ms longer to colour name when a single letter of a word
is coloured relative to al1 letters being coloured. This is another key finding as it funher
confinns the results of previous experiments in which there is a response time cost associated
with the colounng of a single letter for al1 irrelevant stimuli other than incongnient colour words.
This is now the fourth recorded set of stimuli (along with colour nonwords, animal words, and
Reduced Stroop Interference - 95
rows of X's) that experience a response time increase when a single letter is coloured relative to
al1 letters. colour words being the sole expection. It appears increasingly likely that this increase
in response time is offset by a decrease in Stroop interference in the incongruent colour word
condition and that this is what accounts for the results of Besner et al. (1997). 1 have already
offered considerable evidence (past theory and research) to suggest that the use of questionable
control items and the use of button pressing have contnbuted to Besner et al.'s (1997) finding of
an elimination of Stroop interference and their resulting account. When these procedures are
replaced by the more traditional vocal response and more standard controls (e.g., rows of X's).
then reliable Stroop interference is observed. even when a single letter is coloured (Mamurek.
1999; MacLeod, 1999). Thus, it seems more appropriate to view colounng a single letter as a
way to reduce, but not to eliminate Stroop interference. This reduction is what then must be
explained, which is what the present two-process account attempts to do.
Expenments 1 and 2a appear to offer considerable support for the two-process account. even
though this account was not the central focus of these experiments. I now tum to two
experirnents which further investigate the two-process account; namely the differential manner in
which stimuli are processed when a single character is coloured, relative to the entire stimulus
appearing in colour.
Experiment 2b
Though Experirnent 2a provides a more explicit test of whether single Ietter coloured words
are being read during the Stroop task. another possible explanation needs to be further explored.
The possibility that the 20-30 ms reduction in Stroop interference is due to two processes was
previously reviewed and will be given further attention in the next two experiments.
It is nonetheless interesting to consider the manner in which the 30 ms of Stroop interference
Reduced Stroop Interference - 96
was reduced in the Besner et al. (1997) and Besner and Stolz (1999ab) studies, given that their
pattern seems counterintuitive. Recall that response times in the incongment condition were not
reduced to match response times in the control condition when a single letter was coloured;
rather, response tirnes in the control condition rose to match those in the incongruent condition.
The two- process explanation for these results is that colouring a single letter leads the individual
to process distractor words in a different manner that. in tum, eliminates approximately 30 ms of
Stroop interference. For example. one possibility is that colouring a single letter of an irrelevant
colour word causes that word to be processed in a less wordlike manner. thus leading to a
reduction in interference. This reduction. however, rnay be offset by an increase in colour
naming in the single letter coloured case that coincidentally totals about 20-40 ms. This would
occur because colouring a single letter forces the participant to search for the letter. whereas
colouring the entire word allows the participant to remain fixated on one point. This would
explain why control response times rise (seeing as they should be relatively unaffected by Stroop
interference) when a single letter is coloured. whereas incongment trials rise in response time
due to search time but subsequently decrease due to a decrease in interference. This leads to the
illusion that the response times are unaffected by a shift to single letter colouring. were presented
with a single, randornly selected. letter coloured. Participants should take longer to read words
with a single letter coloured than words entirely in colour if the presence of a single coloured
letter disrupts processing. Slower reading times for single lener coloured words would not only
suggest that colouring a single letter slows processing relative to colouring an entire word. but
would also suggest that colouring a single letter may cause a word to be processed in a less
wordlike manner. This does not necessarily mean that words are not being read so much as they
may be being processed differently.
Reduced Stroop Interference - 97
To test this explanation. and the manner in which individuals process words with a single
letter coloured, Experiment 2b was a simple word reading task. The design was similar to the
Stroop task used in Experiment 2a. except that participants were now instructed to read the
words and ignore their ink colours, as quickly and as accurately as possible. Half of the words
were presented entirely in one of four colours (red, blue, yellow. green); the remaining words
Method
Participants. Participants in the present experiment were the same 38 University of Toronto
at Scarborough undergraduates, both male and female. participated for course credit in
Experiment 2a. Though every participant performed satisfactorily in the present experirnent. for
consistency, the 4 participants whose data were excluded fiorn the previous experiment were also
excluded here. Testing time for each participant was approximately 15 minutes.
Materials. The materials in this experiment were 80 noncolour English words. These 80
words comprised the second list that was created from the original 160 words in Experiment 2a.
Unlike the previous expenments, a microphone and voice key was used to record participant
response due to the nature of the task.
Procedure. The word reading study was presented to participants upon completion of the
recognition test fiom Expenment 2a. Alhough many of the aspects of Experiments 2a and 2b
were counterbalanced (e-g.. number of trials. order of lists). Experiment 2b was always
performed following Experiment 2a. This was done to ensure that the stimulus set from
Experiment 2b did not interfere with the recognition test from Experiment 2a. and because
Expenment 2a was considered to be the more crucial of the two experiments.
For each participant, 64 words were randomly selected From the original list of 80. The
experimenter had a printout that listed the order of word presentation so that participants could
Reduced Stroop Interference - 98
be monitored for errors. The experiment consisted of 64 trials in which participants were
instructed to read aloud the words presented to them as quickly and accurately as possible.
ignoring the display colour.
On some tnals, the microphone did not pick up the participant's response and on some trials
the participants rnisread the target word. Ail such incidents were recorded but only the latter
were considered true errors.
Results
True errors (misread words) were made by panicipants on less than 1.5% of trials overall.
This was not deemed problematic because the task in the present expenment was word reading.
not coloiir naming, and there was therefore no reason to expect that error rates should
systematically Vary as a function of whether words appeared fully coloured or with a single letter
coloured. A one-way ANOVA confirmed that there was no difference between the nurnber of
errors made for words appearing fully coloured relative to words appearing with a single letter
coloured, F (1, 33) = 1.9 1. MSe = 1.73, e = 0.18. Indeed. the very existence of the standard
Stroop effect indicates that it is easier for participants to ignore print colour than actual words
and therefore the position of coloured letters should exert little influence. Response time
differences had been expected if colounng a single letter had indeed caused a disruption in
semantic processing, not due to any type of search as in the previous experiments. In addition.
errors did not systematically differ as a function of colouring type: There was an approximately
equal number of errors for fully coloured and single letter coloured words. Aside from tme
errors, response times were excluded fkom analysis when the microphone did not pick up the
initial response, or when narning times were less than 300 ms or greater than 2000 ms. These
constituted less than 1% of the data and did not differ between the fully and singly coloured
Reduced Stroop Interference - 99
conditions.
The purpose of the present experiment was to examine the manner in which individuals
process words with a single letter coloured relative to words appearing entirely in colour. To
examine this, mean word reading times for words appearing fully coloured vs with a single letter
coloured were obtained from each participant. These mean reading times and standard
deviations are shown in Table 18. As expected, participants were siightly faster reading words
appearing fùlly coloured (564 ms) relative to words appearing with a single random letter
coloured (571 ms). This result was nearly. though not entirely. confimed by a one-way within
participants ANOVq with colour type (fülly coloured or single letter coloured) as the
independent variable and colour naming times as the dependent variable. The main effect of
colour type was not significant, F (1. 33) = 2.77. MSe = 422.59, g = - 1 I . though it approached
marginal levels of statistical significance (see Appendix ü).
-4s in Experiments 1 and îa, a second one-way within panicipants ANOVA was conducted to
examine the effect of the position of the coloured letter. Mean reading times and standard
deviations are shown in Table 19. Although there is virtually no difference in reading times
when any of the first four letters are coloured, it took participants quite a bit longer to read words
that appeared with either the fifth or sixth letter position coloured. This difference was
confirmed by a one-way within participants ANOVA, (5, 165) = 3.10. MSe = 1337.36, Q = .O 1.
with the position of the coloured letter serving as the independent variable and reading times as
the dependent variable (see Appendix V). It should be noted that this difference was due solely
to the difference in reading times between the first four letter positions and the last two letter
positions, as there was little response time variance within these two groups of positions (see
Table 19).
Reduced Stroop Interference - 100
Table 18
Esperiment 2b: Mean Reading Times (in ms) and Standxd Dcviations ,as
a Function of Conditions (Al1 Letters Coloured vs. Sinek Letter Coloiircd).
Fully Coloured
Single Letter Coloured
Difference
Note: RT = reading cimes; SD = standard deviation; %E = petccntage of errors
Reduced Stroop Interference - 1 O 1
Esperiment Zb: Mean Reading Times (in ms) and Standard Deviations
ris a Function of Letter Position in Sin& Letter Coioured Words.
Coloured Letter Position RT SD
1 57 1 96
2 568 87
3 567 9 1
4 567 89
5 5 88 103
6 589 102
Note: RT = v o n s e cimes: SD = standard deviation; %E = percentage of erron
Reduced Stroop Interference - 102
Discussion
The results of the present study add some support to the notion that it takes longer to process
stimuli appeanng with a single letter coloured relative to stimuli appeanng fully coloured. This
difference, however. was smaller than might be expected (only 7 ms). Perhaps coloured letters
are more difficult to read off of a black background than are white letters. Thus, any difficulty
that may be associated with reading a word with a single letter coloured could be offset by a
relative ease in deciphenng the Ietters appeanng in white. Another possibility that could account
for these results is practice effects canying over From the first expenment. Though the two tasks
differed, each experiment involved differential colouring of stimuli and the exposure to such
colouring in Experiment 2a may have led to a decreased sensitivity to colouring type in the
present expenment. The built-in experiment order confound does not permit determining
whether this is the case.
An altemate, and perhaps more plausible explanation is simply that words are generally easy
to read itticntiotialfy, regardless of whether they appear fully coloured rather than with a single
letter coloured. In Expenrnents 1 and 2% the task was to identify the display colour and not to
read the word that is presented on the screen. Thus. whereas colouring a single letter rnay
substantially disrupt the automatic and unintentional reading of a distractor word, it may not
disrupt the intentional reading of a target word. The point of the present experiment, however.
was simply to examine whether words appearing with a single letter coloured are processed
differently than words appearing fully coloured, and the present results do provide slight suppon
for this possibility, despite the mal1 effect size. Experiment 3 also provides a test of whether
single letter coloured words and fully coloured words are processed differently in a manner that
Reduced Stroop Interference - 1 O3
is more similar to Expenments 1 and 2a..
Experirnent 2b also exarnined word reading times as a function of the position of the coloured
letter. Unlike the first two experiments, there was a significant main effect of the position of the
coloured letter. with participants taking longer to read words that appeared with the fifth or sixth
letter coloured relative to words that appeared with one of the first four letters coloured.
Although statistically significant, this result is of little practical importance to the present study
given the interest in how colouring a single letter affected the colour naming process and the
unintentional reading of distractor words, not the intentional reading of target words (where the
position of the coloured letter should not actually affect response time). Again, this could be an
artifact of an insufficient number of trials where the fifth or sixth letter is coloured.
Aithough the present experirnent was designed to test the possibility that colouring a single
letter of a word leads to different processing relative to fùlly colouring a word. it is difficult to
apply the present results to those of the first two studies given that a different task was used
(word reading as opposed to colour naming). The present results somewhat support the notion
that colounng a single letter of a word may slow processing relative to fully colounng a word but
this may be a function of the task that was used rather than the colouring of the words
themselves. Thus, to further test how participants process stimuli with a single character
coloured. one further experiment was conducted under colour naming conditions.
Experiment 3
1 have argued that Besner et al.'s (1 997) methodology of colounng a single letter is, by itselE
not a plausible way of eliminating the Stroop effect. To make this argument, 1 have pointed to
various replications of their Experiment 2, as well as a number of unique methodological choices
that they made. It remains possible. however, that colouring a single random letter of an
Reduced Stroop Interference - 104
incongment colour word actual does eliminate approximately 20-30 ms of Stroop interference,
with this reduction in Stroop interference offset by a slowing in response time as participants
search for the coloured letter. If this is the case, it would explain why response times in the
control condition of Besner et al. (1997) appeared to rise whereas response times in the
incongruent word condition appeared not to change. The 20-30 ms reduction in Stroop
interference in the incongment condition would be offset by a slowing in response. thus
providing the appearance that these response times were unaffected when a single letter was
coloured.
The same explanation does not hold for control items. however, as no Stroop interference
should be present in this condition and, therefore, response times should only be affected by the
eara time it takes to search for the coloured letter. This two-process account is plausible, but is
also difficult to test. This is because there is no way to demonstrate that colouring a single letter
of a colour word reduces Stroop interference, independently of an overall slowing of response
times. The two processes seem dependent, and therefore, there is no real way to separate thern.
One can investigate, however, whether colouring a single letter (or character) slows responding
relative to colouring al1 letters. This has already been demonstrated in Experiment Za, but there
is a possibility that even these noncolour words evoke Stroop interference (see MacLeod, 199 1,
pp. 172- 174 for a review).
Experiment 3 was designed to fimher test the notion that colounng a single character slows
colour naming relative to colouring dl characters in a stimulus item. To test this prediction
independently from distractors that may elicit Stroop interference, 1 used a variation of the
praaice task that was used in Expenments 1 and 2. The stimuli on al1 trials were rows of
asterisks with al1 or only one random asterisk in colour. It was predicted that participants would
Reduced Stroop Interference - 105
take longer to indicate the display colour when a single asterisk was coloured relative to al1
asterisks being coloured. This slowing in response should be somewhere in the range of 20 to 30
ms. Such a result would support the idea that colouring a single character reduces Stroop
interference relative to colounng al1 characters. but is accompanied by an overall slowing in
response.
Method
Participants. Twenty-four university undergraduates. both male and fernale, participated for
course credit. Each participant had normal or corrected to normal vision as determined by self-
report and none of the participants had participated in any of the other experiments. Testing time
for each participant was approximately 5 minutes. Due to the very brief duration of this
expenment, it was added to the end of another unrelated experimental session taking place in our
laboratory.
Materials. The materials were rows of astensks which were equivalent in length to the
colour and noncolour words used in the first two expenments (i.e., 3.4. 5. or 6 asterisks in
length).
Procedure. To familiarize participants with the button pressing procedure that was to be
used during the experiment, participants initially perfonned 24 practice trials that were identical
to the types of trials contained within the expenment. With the exception of the number of
practice trials. the procedure was identical to the Stroop tasks in Experiments 1 and 2a. with
participants identifjmg the display colour of a fully coloured row of asterisks or of a single
coloured asterisk within the row. rather than words and nonwords. Following the familiarization
task participants completed the actual64 experirnental items.
Resul ts
Reduced Stroop Interference - 1 O6
Mean naming times and standard deviations were calculated for each participant. Colour
naming times for rows of asterisks appeanng fully coloured (677 ms) were 20 ms faster than for
rows of asterisks appearing with a single astensk coloured (697 ms) (See Table 20). A one-way
within participants ANOVA was perfomed with colour type (al1 asterisks or a single coloured
astensk) as the independent variable and colour narning times as the dependent variable. This
analysis indicated that the 20 ms difference in naming times between fùlly coloured rows of
asterisks and rows of asterisks with a single asterisk coloured words was significant. F ( 1. 24) =
7.90, MSe = 597.84, p = . O 1 (see Appendix W 1). There was no effect of the position of the
coloured asterisk (see Table 2 1 for means and standard deviations), F (5, 120) = 1.65, MSe =
7 186.22, p = .15 (see Appendix W2).
Error rate analyses demonstrated no difTerence in error rates as a function of colour type, F ( 1.
24) = 1.23. MSe = 0.0006, g = 0.28, or as a function of coloured asterisk position, F (5, 120) =
1.16, MSe = 0.003, p = 0.33 (see Appendices XI and X2).
Discussion
Due to the nature of the present distractors, it was not necessary to examine error rates as a
function of colounng type or position of the coloured asterisk because asterisks provided little, if
any, distraction to participants. In addition, though there was a marginally significant effect of
the position of the coloured character, there was no intuitive or interesting pattern of colour
naming times as a function of the position of the coloured character. Again, none of the
anticipated patterns of positional results were prevalent, thus lending credence to the notion that
participants either fail to develop a strategy for colour naming or develop a strategy that does not
lend itself to an easily analyzable pattern of results regarding coloured character position.
The results of the present experiment were exactly as expeaed. Participants took longer to
Reduced S troop Interference - 1 O7
Table 20
Ewenment 3 : Mean Reaction Times (in ms). Standard Deviations. and Enor Rates to Name
Colours as a Function of Condition (Al1 Asterisks Coloured vs. Single Asterisk Coloured).
AI1
Single
D iffe rence
Note: RT = response tirnes; SD = standard deviation; O/oE = percentage of errors
Reduced Stroop Interference - 1 O8
Table 18
Emcriment 3: Mean Reaction Times (in ms). Standard Deviations. and Error Rates
to Name Colours as a Function of Coloiired Asterisk Position in the Single Asterisk
Coloured Position.
Coloured Letter Position RT SD %E
1 674 1 14 2.7
2 685 116 6.8
3 71 1 12 1 3 .O
4 702 142 1.9
5 698 128 1.3
6 737 18 1 O
Note: RT = response tirnes; SD = standard deviation: %E = percentage of errors
name the display colour when a single astensk was coloured relative to al1 asterisks being
Reduced Stroop Interfierence - 109
coloured. This slowing in response was right around the 20 ms range that was demonstrated for
control items in the Besner et al. (1997), and MacLeod (1999) studies. as well as the present
Experiment 1. It should be noted that this slowing in response times would have been larger,
except that two participants showed a pattern of results that were in the direction opposite
expectation (these participants were approximately 100 ms faster indicating the display colour
when a single character was coloured relative to al1 characters being coloured). Without these
participants. the difference in response times would actually be closer to 35 ms.
Thus, the evidence does suggest that colouring only a single letter of a coloured item slows
down responding to colour by approximately 20-30 ms. This leads to the illusion that colouring
a single letter of a colour word does not affect response times relative to colouring al1 letters.
For control items, where there is ostensibly no Stroop interference occurring, colouring a single
letter leads to a slowing in a response which causes response times to nse and match incongruent
word response times. Again though, despite a relative ease in demonstrating that colouring a
single letter leads to an increase in response time, it is difficult to show that colouring a single
letter leads to a reduction in interference when it is always accompanied by this increase in what
would appear to be search time. Due to the fact that response time increases have been
demonstrated for al1 irrelevant word types except colour words. it seems reasonable to conclude
that an additional process is leading to a corresponding response time decrease when a single
letter is coloured.
These results could be seen as suggesting that the Stroop effect has been eliminated as Besner
et al. (1997) conclude, but 1 have already suggested why this may not be the case. A strong
argument for my position seems to be a high probability that some Stroop interference is
occumng in Besner et al.3 (1997) control condition (e-g. E T , BLAT), as was suggested by the
Reduced Stroop Interference - 1 10
pattern of results in Experiment 1, as well as by past findings regarding the first letter of an
incongruent colour word (e.g., Regan, 1978). Consequently, Stroop interference would still be
present in each stimulus type (colour words and colour nonwords), despite an equivalence in
response times across conditions. A more detailed explanation of the possible problems
associated with these control items, as well as other Besner et al. (1997) procedures, will be
reserved for the General Discussion section.
One other possible explanation for the results of the Besner et al. (1997). MacLeod (1999).
Marmurek (1999). and the present studies is that colour words are in some way immune to the
slowing in response that seems to occur when a single letter is coloured relative to colouring al1
leners in other distractor words. There are, however. at least two pieces of evidence that would
suggest that colour words are not immune to this slowing in response time associated with
colounng a single letter. First. there is nothing in the literature to suggest that there is anything
"special" about colour words that should make them immune to the slowing in response
associated with colounng a single letter. Second. in seneral. there was a slight rise in response
times for colour words when a single letter was coloured in the present expenments. and in
Besner et al. ( 1997). MacLeod ( 1999), and Marmurek ( 1999). indicating that colour words were
at least being slightly influenced by the single letter coloured manipulation. Thus. it may be that
when one colours a single letter of a colour word. the average reduction in Stroop interference is
approximately 20 ms whereas the average increase in response times is approximately 30 ms.
Regardless, it does not seem likely that colour words are immune to slowing when a single ietter
is coloured.
Reduced Stroop Interference -1 1 1
General Discussion
The present series of experiments was conducted to further examine the possibility that the
Stroop effect can be eliminated, a claim put forth in articles by Besner et al. (1997) and Besner
and Stolz (1 999a,b). These researchers claimed that the Stroop effect could be eliminated by
colouring only a single letter and not al1 of the letters of an incongment colour word. I have
pointed out a number of possible problems with the Besner et al. (1997) procedure (e-g., control
stimuli, response mode), and have reviewed a number of replications and partial replications of
the Besner et al. (1997) work that have not completely elirninated the Stroop effect. 1 have
argued that to elirninate the Stroop effect via preventing word reading. one would have to show
that distractor words are not being read (and thus. not providing interference).
Summary of the Findings
Although Besner et a1.k (1997) results demonstrate an equality in colour naming response
times between fully coloured words and words with a single letter coloured, a simple reliance on
naming time differences is not definitive in demonstrating whether distractor words are beinç
read. Thus, the present Experiment 2a was designed to provide a more explicit test as to whether
distractors were being read on Stroop trials. A two-process account was introduced to account
for the results of Besner et al. (1997) and two subsequent expenments were conducted to test this
view (Experiments 2a and 3).
The purpose of Experiment 1 was to replicate and extend Experiment 2 from Besner et al.
(1997). with the additional goal of examining the effect of the position of the single coloured
letter. Although the key aspect of the basic pattern of Besner et al.'s (1997) results replicated. -
interference decreased for single-letter-coloured words relative to fully coloured words - there
was no evidence to suggest that the Stroop effect had been eliminated. Colounng only a single
Reduced Stroop Interference - 1 12
letter appeared to decrease, but not to elirninate, Stroop interference. Thus, the present
Experirnent 1 adds to a growing literature of replications and partial replications of Besner et al.
(1997) and Besner and Stolz (1999a/b), that have not demonstrated an elhination of the Stroop
effect (e.g., MacLeod, 1999; Marmurek, 1999).
Error rate analyses from Experiment 1 also discounted the Besner et al. (1997) claim that
colounng a single letter leads to a disruption in semantics. Overall, participants made more
errors when incongruent colour words appeared with a single letter coloured relative to fully
coloured. Were Besner et al. (1997) correct in claiming that colounng a single letter disrupts
semantic processing of distractors, then fewer errors would be expected when a single letter is
coloured, assurning that errors are the result of an incorrect response to the distractor words.
The purpose of Experiment 2 was to provide a more explicit test of how distractor words are
processed under these conditions. Experiment 2a examined recognition rates for distractor
words that were presented dunng an initial Stroop colour naming study phase. Rather than using
colour words and colour nonwords, each Stroop trial consisted of a different English language
word. Participants were then subjected to a surprise recognition test to examine tneir memory
for the to-be-ignored distractor items. Collectively. the recognition accuracy and response time
data indicated that colouring a single letter does not disrupt semantic processing of distractor
words and it is therefore more likely that colounng a single letter reduces Stroop interference
while simultaneously increasing response time. Consequently, the two-process account was
given further scrutiny in Expenments 2b and 3 .
Enperiment 2b further examined the marner in which words are processed when they appear
with a single letter coloured relative to having al1 lerters coloured. Using an intentional word
reading paradigm, there was a mere 7 ms benefit for fully coloured words over single Ietter
Reduced Stroop Interference - 1 13
coloured words in terms of reading time. The most plausible explanation for this is the
possibility that different processes occur when individuals read words intentionally rather than
incidentally. This is of little consequence to the present iine of research, however, given that
Stroop research deals exclusively with colour naming of only incidentally read words.
Expenment 3 was an examination of the two-process account that has been posited to account
for Besner et ale's (1 997) results. In an attempt to tease apart these two processes, a Stroop task
was used in which rows of astensks appeared as distractors rather than words. The results of the
expenment indicated that it does take participants approximately 20-30 ms longer to name a
display colour when only a single character is coloured relative to al1 characters being coloured.
This result supports the notion that colounng a single letter may lead to a reduction in Stroop
interference. which is in tum offset by a slowing in response.
The present experiments were also designed to test the influence of the position of a coloured
Ietter on response. Previous research (e-g. Regan. 1978) had demonstrated that much of Stroop
interference may be attributable to the first letter or letters of an incongruent colour word (e-g..
the letter 'Y in blue) and, therefore. 1 sought to determine the influence of letter position on the
present response time and error data. Although positional analyses were useful in further
demonstrating that the Besner et al. (1997) control stimuli may be inappropnate (a point which
will be expanded upon shortly), there were no other sijgificant effects of letter position. Nor
were any interesting or intuitive patterns of results observed for letter position across the set of
experirnents. This is only a minor disappointment to the present line of research and does not
detract frorn the other important findings that have already been reviewed. In the upcorning
section, 1 will hrther outline the issues that have been raised to this point, as well as considering
the implications and interpretations of the present results. Possible methodological problerns
Reduced Stroop Interference - 1 14
will be considered, and ideas for future research in this area will be suggested.
Where Does the Present Study Fit?
The present Expenment 1 is now the third known attempted replication of Besner et al.
(1 997). Experiment 2, in addition to the further studies by Besner and Stolz ( 1999% b).
Previously, both Marmurek (1 999) and MacLeod ( 1999) have performed replications of the
original Expenment 2. as well as partial replications in which different control stimuli and
response modes were used. In al1 of the straight replications of Besner et al. ( 1997). Besner et
al.3 ( 1997) basic pattern of reduced interference was replicated. though Marmurek ( 1999) failed
to demonstrate an elimination of Stroop interference. as was also the case in the present
Experiment 1. MacLeod (1999) and Besner and Stob (1 999) both observed an "elimination" of
Stroop interference though this elimination was wiped out by MacLeod (1999) when he switched
to different controls and vocal response.
Marmurek (1 999) and the present Experiment 1 both observed the difference between control
and incongrnent trials to be closer to 20 ms than O ms in the sinlge letter coloured condition. In
addition, when Marmurek ( 1999) and MacLeod ( 1999) performed partial replications of Besner
et al. (1 999) using different control items (animal names or rows of X's) and different response
modes (vocal rather than button pressing). substantial Stroop interference was always observed.
even when only a single letter was coloured. Thus. the present Experiment 1 adds to the growing
literature that demonstrates that colouring a single letter of a distractor word does not. by itselt
eliminate Stroop interference. although interference is consistently reduced by this manipulation.
The present Expenment 2a, however. is the first attempt to apply an explicit memory test to
the Besner et al. (1997) paradigm in an attempt to determine the manner in which distractor
words are processed when a single letter is coloured relative to the entire word. 1 have argued
Reduced Stroop Interference - 1 1 5
that Besner et d.'s (1997) reliance on equivalence in response times is insufficient grounds to
conclude that distractors are not read when a single letter is coloured. Indeed. the present results
demonstrate that distractor words are being read, regardless of the manner in which they are
coloured. Recognition rates for words appearing with a single letter coloured during an initial
Stroop task were equal to those for words appearing fully coloured during the same task. In
addition, each of these word types was recognized at a rate well above baseline (as detennined
by false dams to words not presented during the Stroop task).
Error rate analyses funher supplemented the present claim that colouring a single letter does
not lead to a dismption of semantics for distractor words. In the present Experirnent 1, the error
rate for incongment colour words increased when they appeared with a single Ietter coloured
relative to fully coloured. Had colouring a single letter disrupted semantics, then it would be
expected that error rates for incongment colour words would decrease when a single letter is
coloured. assuming that errors are the result of an incorrect response to irrelevant words.
Marmurek (1999) observed a sirnilar (if not greater) increase in error rates for incongruent colour
words when a single letter was coloured relative to al1 letters, and Besner et al. (1997) obtained
no change across these two conditions. Clearly, these results suggest that distractor words are
being read when a single letter is coloured and. therefore. this method of colouring does not lead
to a dismption of semantics nor to an elimination of Stroop interference, contrary to Besner et al.
(1 997).
It does seem entirely reasonable. however, to suggest that colouring a single letter of a
distractor word leads to a rediictioii in Stroop interference, likely in the 20-30 ms range. This
reduction in Stroop interference is then offset by an increase in overall colour narning response
time in the single letter coloured condition which, from the present expenments, not
Reduced Stroop Interference -1 16
Experiment 3, we can determine to be somewhere in the range of 20-40 ms. This explanation
represents the two-process account for the results of Besner et al. (1997), an account which has
been argued for extensively throughout this thesis.
There are a number of aspects of the present data that provide suppon for the two-process
view. First, there is a consistent increase in response time when a distractor appears with a
single letter coloured relative to appearing with al1 letters coloured. In Experiment 1. there was a
colour naming increase of 13 ms for incongruent colour words and of 36 ms for colour nonwords
when a single letter was coloured relative to al1 letters being coloured. Note that this increase is
much srnaller for incongruent colour words, the condition most likely to be offset by a reduction
in Stroop interference. In Experiment 2% there was a naming increase of 40 ms when a single
letter was coloured relative to al1 Ietters being coloured. Finally. in Experiment 3, the result is
especially clear. There was a narning increase of 20-30 ms when a single asterisk was coloured
relative to al1 asterisks being coloured. Thus, an increase in the colour naming response time has
now been documented for four separate types of lexical and nonlexical stimuli when a single
character is coloured relative to al1 characters: Colour words, colour nonwords, assoned 3-6
letter English words, and rows of asterisks. These naming time data provide unequivocal support
to the argument that colounng a single letter increases naming response time relative to
colouring al1 letters of the irrelevant word.
As has already been pointed out, it is difficult to determine whether colouring a single letter
reduces Stroop interference in the absence of an increase in response time. There are. however,
key aspects of the present data that suggest that this may be the case. Consider again the just-
reviewed differences in colour naming time when a single letter is coloured relative to al1 letters.
Of the four registered increases in naming response, the srnallest increase occurs when a single
Reduced Stroop Interference - 1 17
letter of an incongruent colour word is coloured. The incongruent colour word condition is the
one most associated with Stroop interference and. therefore, the one most likely to evidence a
decrease in interfierence when a single letter is coloured. This appears to be the case in the
present Experiment 1. Were Stroop interference not being reduced, there would be no reason to
think that incongruent colour words should be any less affected by colouring a single Ietter than
are colour nonwords or other English language words. The only other possible explanation for
the relatively small increase in naming response when a single letter is coloured is that colour
words are in some way immune to these effects relative to colour nonwords and other English
words. It has already been pointed out, however, that there is no reason, either empirically or
theoretically, to believe this to be the case.
The second aspect of the present data that supports the possibility that colouring a single letter
reduces Stroop interference is the pattem of response time resuits in the present Experiment 1. as
well as in Besner et al. (1997) Experiment 2, and in MacLeod (1999). In Besner et al. ( 1 997)
and al1 replications and extensions. response times in the control condition rise to match (or
nearly match) response times in the traditional incongnient condition, whereas incongruent times
appear to remain unchanged. To argue that the Stroop effect can be eliminated. one would
expect that the opposite pattem of results would be obtained: Response times in the incongnient
condition should have decreased to match response times in the control condition. This unusual
pattern of results is readily explained by the two-process account. In the control condition, there
is ostensibly no Stroop interference to be elirninated and, therefore, response tirnes are only
afi?ected by the increase associated with switching From a fully coloured word to a single letter
coloured word. In the incongruent colour condition, however, there is an abundance of Stroop
interference that cm be reduced. Colouring a singie letter leads to the expected increase in
Reduced Stroop Interference - 1 18
colour naming but is offset by an approximately equal decrease in S troop interference, presenting
the illusion that naming times have remained unchanged.
Final Words on Besner et al. (1997)
The present results provide support for a two-process account. but also demonstrate that it is
inappropriate to think of the Besner et al. (1997) and Besner and Stolz (1999ah) results as
representing an eiirnination of the Stroop effect. Colouring a single letter in fact does not appear
to dismpt the semantic processing of irrelevant words, contrary to the claim of Besner et al.
(1 997). These words are clearly being read when a single letter is coloured, despite explicit
instructions to the contrary, as evidenced by recognition rates for these words that are far above
baseline. In addition. recognition rates for words appeanng with a single letter coloured were
equal to rates for words appeanng fully coloured. opening up the possibility that colouring a
single letter does not even lead to differential processinç of distractors relative to colouring al1
letters.
If colouring a single letter leads to a reduction in Stroop interference, then why is it that
Besner et al. (1997) obtain what appears io be a complete elimination of Stroop interference
when their response time data are considered. A number of aspects of the Besner et al. ( 1997)
and Besner and Stolz (1999ah) studies have already been questioned in the present research and
will be reiterated here as the response time and error rate data in Experiment 1 seem to confinn
these concerns.
The first concem with the Besner et al. (1997) and Besner and Stolz (1999ah) rnethodologies
was their use of button pressing as a response mode. Though the present study also used button
press as a response mode (for consistency). I have reviewed two partial replications of Besner et
al. (1997) where the researchers used vocal response. In both Marmurek (1999) and MacLeod
Reduced Stroop Interference - 1 19
(1999). the Besner et al. (1997) stimuli and methodology were used with vocal response; in both
of these studies, substantial Stroop interference was recorded in the single-letter-coloured
condition. Thus, it seems reasonable to conclude that the button press response was a key part of
the reason that Besner et al. (1997) observed a mere 30 ms of initial difference between
incongment colour words and control items - Stroop interference - when words appeared fully
coloured. Of course, smaller amounts of initial interference are also easier to elirninate.
The second main concern with the Besner et al. (1997) methodology revolves around the
appropriateness of their control stimuli. Although there is no universally agreed upon control
item for Stroop research - indeed. there could not be because controls always hinge on the
question being asked - I have suggested that the Besner et al. (1997) colour nonwords rnay be
inappropriate as they could readily elicit Stroop interference themselves. If the first letter (or
letters) of an incongruent colour word can elicit Stroop interference, then it would be expected
that the response time difference between incongment colour words and Besner-type colour
nonwords would be minimal because colour nonwords contain the first two letters of incongruent
colour words. This is indeed the case in the Besner et al. (1997) data, as there is only 30 ms in
response difference between incongment colour words and their controls when the words appear
fully coloured. Had different controls been used (rows of X's or other English words), then a
larger difference in response time would be expected between incongruent colour words and
controls appearing fully coloured.
There are a number of aspects of the present response time and error rate data that seem to
corroborate the daim that the first lener (or letters) of an incongnient colour word elicit Stroop
interference. First. in the present Experiment 1, there was no difference between incongnient
colour words and colour nonwords when the first or second letter appeared in colour. When the
Reduced Stroop Interference - 120
third or fourth letters were coloured, however, significantly longer response times were observed
for incongment colour words relative to colour nonwords. No difference was recorded when the
fifth or sixth lener was coloured, but there may have been too few triais containing these letter
position to rnake useful conclusions. Nonetheless, the response time data for the first four letter
positions are consistent with what would be expected if the first letters of incongruent colour
words elicit Stroop interference. The first two letters of colour nonwords are identical to the first
two letters of incongment colour words and, therefore, this response time equivalence is to be
expected. The third letter of Besner-type colour nonwords, however. is the point at which these
words are confirmed not to be colour words and this is also the point where response times and.
therefore. Stroop interference. drop relative to incongruent colour words. Were colour nonwords
appropriate controls (Le.. they did not elicit Stroop interference themselves), response times
should be greater for incongruent colour words in every letter condition.
The second piece of evidence for colour nonwords eliciting Stroop interference is denved
€rom the pattern of error rate data as a function of the position of the coloured letter. The error
rate data are actually very similar to the just reviewed response time data. There was no
difference in error rates between incongrnent colour words and colour nonwords when either the
first or second letter was coloured. When the third letter appeared coloured. however.
substantially more errors were observed for incongruent colour words than for colour nonwords.
Again. this is the point at which colour nonwords are confinned not to be colour words and.
therefore. the point at which error rates should be expected to drop.
Taken together, the error rate and response tirne data as a fùnction of letter position seem to
corroborate the claim that Stroop interference is present in Besner et al.'s (1997) control
condition. It c m therefore be concluded that the equivaience in response time data in Besner et
Reduced Stroop Interference - 12 1
al. (1997) Experiment 2 is not solely attributable to the colouring of a single letter. Rather, it
appears as though the initially srnall difference between fûlly coloured incongment colour words
and their controls is a function of bunon responding and the presence of Stroop interference in
the somewhat incongment control condition. It is reasonable to believe that colounng a single
letter reduced approximately 30 rns of Stroop interference From incongruent colour words, but it
surely cannot be claimed that simply colouring a single letter of a distractor eliminated Stroop
interference.
Thus, 1 am confident in concluding that whereas colounng a single letter of an irrelevant word
reduces Stroop interference, it is not the case that this colouring methodology elirninates Stroop
interference. Clearly, distractors are being read in the present study when they appear with a
single letter coloured. In fact, there does not seern to be any diflerence in the manner in which
single letter coloured words are processed relative to hl ly coloured words because Experiment 2
shows that recognition rates for these two word types are equal. The present error rate and
response time data are also indicative of problems in the basic Besner et al. (1997) methodology.
Clearly there is reason to believe that the response modality and control items used by Besner et
al. (1997) may be inappropriate, and shouid be replaced if one wishes to hnher examine the
effects of colouring a single letter of distractors. To this extent, the studies of both Marmurek
( 1999) and MacLeod ( 1999) are usehl in presenting a more complete story of how distractors
are processed when a single letter is coloured.
As has already been outlined, there is a findamental problem in interpreting a change in
amount of interference (a difference score) when there is also a change in the control condition
(against which the difference score is computed). Did interference decrease in the incongment
condition or did it increase in the control condition, or was there just some overall slowing in the
Reduced Stroop Inteference - 122
single-letter coloured condition, perhaps due to the necessity to search for the colour
information? This complicates interpretation yet also forms the basis for the two-process
explanation set out here. The obtained pattem of results in the present experiments (as well as in
the other previously reviewed replications of Besner et al.) are what would be expected under the
two-process account that has been outlined. In particular, the finding that the colouring of a
single letter leads to a response time increase in al1 conditions (colour nonwords, noncolour
English words, animal words, rows of X's) other than colour words seems to be strong evidence
that a second process is contnbuting to the colour word condition. This process likely
counteracts the increase in response time that would be expected due to extra search tirne. 1 am
therefore confident in concluding that this is the most appropriate explanation for the present
results, as well as the results of Besner et al. ( 1 997) and their successors.
Why Does Letter Position Not Matter?
Due to the work of Regan (1978) and Logan and Zbrodoff (1998). 1 had expected to find an
interestindintuitive pattem of response time and error rate results as a fùnction of the position of
the coloured letter. Specifically, 1 was expecting to observe substantial Stroop interference when
the first letter of an irrelevant colour word appeared coloured and then a systematic decrease
when the second through sixth letter positions were coloured. Though positional analyses were
worthwhile in demonstrating that the Besner et al. (1997) control items appear to elicit Stroop
interference, there were no other significant positional effects observed.
I outlined a view that is still highiy efficient, but does not lend itself to a predictable pattern of
results, seeing as this pattern would be a function of the random order in which each triai is
presented. Under this new view. participants do not retum their attention to the left side of the
screen when each new stimulus trial is encountered. rather their attention remains fixated on the
Reduced Stroop Interference - 123
general area where the previous response colour was encountered. For example, imagine that on
the first trial the word GREEN appears with the fourth letter coloured. Initially, participants
attentionally scan across to the first letter so that a response may be made. Once the naming
response is made, however, participants remain attentionally fixated on the area where the fourth
letter of GREEN appeared. If the word that follows is either hlly coloured (and at least four
letters long), or also appears with the fourth Ietter coloured, then no additional search is needed
before a response can be made. Because half of the trials contain fuily coloured words.
participants will not to have to engage in any search at least 50 % of the time (and probably more
than this seeing as the same letter position might occasionally appear in colour on two
consecutive trials). Search will only be engaged when a word appears with a single letter
coloured that is not the fourth letter. Response time should then be a function of how far away
from the last coloured position the current coloured letter is.
Originaily, the goal of exarnininç Ietter position data was to examine the influence of the
position of the coloured letter solely due to the possibility that this was an integrai aspect of
response. Though the current pattern of results does not support this notion, it has not interfered
with formulating a reasonable explanation for the current results, as well as the results of Besner
et al. (1997). This explanation is independent of the position of the coloured letter and therefore,
it is reasonable to suggest that coloured letter position is not necessarily integral in colour
namng.
Where then does this leave the works of Regan (1978) and Logan and Zbrodoff (1998)?
These researchers have argued for the importance of the position of the coloured letter in Stroop
interference. In addition, Logan and Zbrodoff have argued that the first letter of an incongruent
colour word may be solely attributable for Stroop interference. Clearly the present research
Reduced Stroop Interference - 124
demonstrates that Stroop interference can occur at other letter positions and, therefore, their
claim is too strong. There are, however, a number of aspects of the present data that suggest that
the first lener of incongruent colour words may play an important a role Stroop interference.
First, among al1 letten, the first letter is the position at which errors occur most fiequently.
Assurning that errors are the result of irnproper response to the distractor worddetter, the error
rate data seem to corroborate the claims of Logan and Zbrodoff A sirnilar pattern, though one
Iesser in magnitude, is observed when the second letter is coloured relative to al1 later colour
positions.
It is also the case that substantial Stroop interference is observed with regard to response
times when the first two letters of incongruent colour words are examined. Recall that error rates
and response times for words with the first or second letter coloured did not differ when 1
compared incongruent colour words to Besner et al.3 (1997) colour-like nonwords. When
comparing these two item types with the third letter coloured, however. there was a response
time and error rate advantage for the colour-like nonwords (meaning that response times are
faster and error rates lower for colour-like nonwords relative to incongment colour words). The
third letter is also the point at which colour-like nonwords are confirmed not to be incongruent
colour words and therefore it is intuitive that Stroop interference should be reduced here. Earlier
1 used this as support for the daim that the Besner et al. (1997) nonwords were an inappropriate
baseline as they too elicit Stroop interference. In the fiame of the current argument, however,
the present results can be taken as evidence that although the first letter of incongment colour
words does elicit Stroop interference, interference is not solely attributable to the first letter.
Clearly Stroop interference is observed at other letter positions, despite the fact that more of it is
observed for the first letter.
Reduced Stroop Interference - 125
Recently in Our lab, MacLeod (2000) perforrned an expenment where Stroop interference was
cornpared for colour words, rows of X's, and rows of repeated first letters frorn words (e.g.
BBBB, GGGGG, YYYYYY). The prediction was that rows of repeated first letters might
actually elicit more S troop interference than incongruent colour words, if in fact Stroop
interference is due solely to the first letter. This, however, was not the case. Although more
Stroop interference was observed for rows of repeated letters relative to rows of X's. the most
Stroop interference was stiil observed for colour words. Incongrnent first letters did elicit a level
of Stroop interference but are clearly not solely responsible for Stroop interference given that
longer response times were recorded for colour words.
It may be that there is an individual letter component to Stroop interference but there is also
an effect of the entire word/semantics above this effect. Again, these findings do not add or
detract from the present results. Although the present studies have not found any interesting
pattern of results as a fùnction of the position of the coloured letter. it is also the case that they
have done nothing to detract from the work or theory of Regan (1978) or Logan and Zbrodoff
(1998). The full effect of the position of the coloured letter within an incongruent colour words
still remains an issue, despite being able to form an explanation for the current results that
operates independent of letter position.
Suggestions for Future Research
To test the possibility that the Besner et al. (1997) controls elicit Stroop interference, it would
also be interesting to perforrn a traditional Stroop task in which the Besner et al. (1997) colour
nonwords are used in place of incongruent colour words, with either the MacLeod (1 999) rows
of X's or the Mamurek (1999) animal words as controls. Due to the fact that the Besner et al.
(1997) controls are nonwords, they should not elicit any Stroop interference if they ostensibly
Reduced Stroop Interference - 126
have no meaning attached to them. It has been shown, however, that even the first letter of an
incongruent colour word can produce Stroop interference (e.g., Regan, 1978; see MacLeod,
199 1, pp. 174- 175 for a review ). Because the colour-like nonwords contain the first two letters
of colour words, 1 have argued that these words rnay be eliciting Stroop interference.
Thus, it would be worthwhile to design a study where colour nonwords, animal names, and
rows of X's are a11 used as distractors. The pattern of results of such a study would demonstrate
whether Stroop interference was present for colour nonwords relative to these other control
types. Other English language words have been shown to elicit some Stroop interference (e-g..
Klein, 1964). though not as much as incongnient colour words. Rows of X's. it could be argued.
do not elicit any Stroop interference. though it has been argued (including by Besner et al..
1997). that they are inappropnate controls on the basis that they are unwordlike. Thus. one
might expect that other English language words should elicit more Stroop interference than the
colour nonwords, if the latter are indeed (rue controls with no meaning attached to thern. If these
colour nonwords do elicit Stroop interference. however. one might expect colour naming times
that are equal to or greater than those for other English language words.
The only probiem with this study is that actual colour words would no longer be present.
This is crucial as it may be the presence of colour words in the Besner et al. (1997) study that
would cause participants to view the colour nonwords in a meaningfil manner. On their own.
these nonwords may have little meaning, but when CO-occumng up with actual colour words. it
is easy to see how a comection may be made between these two types of stimuli. For example.
aside fiom the word RED. the nonword RET is very sirnilar to the words RAT. ROT. and PET.
arnong others. Thus, a second experiment (or a second block of trials) could be nin in which
rows of X's were replaced with colour words to investigate whether there is any difference in
Reduced Stroop Interference - 127
colour narning times when colour words serve distractors, relative to colour-like nonwords or
animal words.
One additional way to investigate the manner in which distractor words are processed when a
single letter is coloured would be through the use of tMRI technology. Recently, some
researchers have begun to use technology in their Stroop studies to compare performance
on colour naming in the classic incongruent condition relative to a number of controi conditions
(see MacLeod & MacDonald, 2000, for a review). Such an expenment would be large in
magnitude as it would require a number of different comparison groups, or to have participants
perform a considerable number of tasks. The purpose of the experiment would be to examine
whether there is a difference in the processes that are evident when a single letter of a distractor
word is coloured relative to al1 letters being coloured. The design of the experiment would have
participants perfonn 4-8 tasks with the conditions as follows:
1) colour naming with a full row of asterisks coloured 2) colour naming with a single random asterisk coloured in a row of astensks 3 ) normal word reading (white pnnt on a black background) 4) word reading with the entire word coloured 5) word reading with a single letter of a word coloured (other letters appearing in white) 6) Colour narning with an entire distractor (X's, nonwords or animal words) coloured 7) Colour narning with a single letter of a distractor (X's, nonwords, or animal words)
coloured S) Same as 6 and 7 with colour words used as distractors
Essentially, these conditions comprise the experimental and practice stimuli used in the present
study. though an attempt has been made to present the tasks independently so that the processes
that drive them can be disassociated. This methodology would allow for an examination of the
different regions of the brain that are activated and, therefore, the different processes that would
be invoked dunng each task. Though the present results do not seem to indicate that differential
processing occurs when a single letter is coloured relative to al1 letters, fMRl data would provide
Reduced Stroop Interference - 128
a more explicit examination of this. Do areas associated with reading show the same activation
in the single letter as in the fùlly coloured condition?
Based on the present analyses, a key point of interest would be the processes that are invoked
when participants read words intentionally rather than incidentally. Though £MRI would provide
funher evidence that distractors are being read automatically when a single letter is coloured. the
present data raise the issue of whether differential processes are used when a word is read
intentionally vs. incidentally (i.e.. automatically). tMRl would be a very usehl tool for testing
this possibility and may lead to a new line of research and. consequently, a new way of thinking
about how we process words that we encounter.
The Big Picture
The present thesis has provided sufficient evidence to dispute the claim that colounng a single
letter of an irrelevant word eliminates Stroop inteference. as put fonh by Besner et al. (1997).
Their claim that colouhg a single letter biocks the automatic reading (and therefore. the
semantic processing) of irrelevant words is placed in serious doubt by the results of the present
research. A number of aspects of the present results. as well as the results of partial replications
of Besner et al. (e.g., Marmurek, 1999; MacLeod, 1999) suggest that irrelevant words are. in
fact. read when they appear with a single letter coloured and that it was other methodological
aspects of Besner et al. (1 997) that led to their apparent elirnination of the Stroop effect. The
most convincing argument against this claim is the relatively strong recognition rates for words
appearing during a Stroop task. Although Besner et al.'s (1997) single letter coloured
manipulation definitely seems to reduce Stroop interference, it is clear that a different
explanation (other than that of elimination) is required.
To account for these results. a two-process explanation was introduced, which posits that the
Reduced Stroop Interference - 129
colouring of a single letter forces participants to search for the desired response (display colour),
thus increasing search time. In the case of colour words, however, this search rnay also lead
participants to process irrelevant words in a less wordlike manner, thus leading to a decrease in
interference roughly equal to the increase in search tirne. Although the present experiments
provide considerable evidence that colouring a single letter of an irrelevant word leads to an
increase in response time relative to colouring al1 letters, it is admittedly difficult to show that
colouring a single letter leads to a reduction in interference when it is always accornpanied by
this increase in search time. Experiment 3 does, however, help to reinforce this claim. For the
present, it does seem reasonable to conclude that the single letter coloured manipulation does
lead to a decrease in Stroop interference given that response times rise for al1 distractor types
(cotour nonwords, animal words, noncolour words, rows of X's) other than colour words when a
single letter is coloured in the Stroop task.
Clearly. however, fbrther research is necessary to corroborate or disprove the two-process
account. Nonetheless. the present research restores the notion that certain automatic processes
(in this case, word reading) cannot be prevented from occumng in rnost circumstances.
Specifically, colouring a single letter does not prevent the individual from reading irrelevant
words. despite the fact that it may lead to these words being processed in a dif3erent manner.
This is not to say, however, that there are no situations under which automatic processes will be
prevented from occumng. As has been pointed out. automaticity is clearly contextual in nature.
The present research indicates that simply colouring a single letter of an irrelevant word.
however, is not one of the situations in which automatic processes are prevented. It is, therefore.
viable to conclude that Besner et al. (1997) and Besner and Stolz's (1999ah) claim that the
Stroop efYect can be eliminated and that existing accounts of automaticity are too strong is, in
Reduced Stroop Interference - 130
itselc too strong.
Reduced Stroop Interference - 13 1
Reduced Stroop Interference - 1 3 2
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Reduced Stroop Interference - 13 7
Appendix A: Word Lists For Experiments 2a and 2b
List One
act cut dog ear fu n hen ice kid lesi lot
mud net oil pad Pea Sun ta P tie van
List Two
cap day dot fan fog hat hog jar lap lie man mob oak owl Pet pie Pot sin top web
cake chip deck edge feet frog hand hill joke la ke mail nest pa* PumP seat shop star tank vine wave
aunt card dart dish farne food hair heat home king loc k mask mile moon nose play sait sin k time wine
chain class dance d raft fault flarne house kn ife laugh nerve month night patch phone queen shape smile thumb train watch
check chant ditch drain earth feast fruit horse judge light lunch mouse match paint peach plane score toast voie wtieel
cannon debate dinner hammer infant jacket kitten ladder lesson middle parcel pe b ble sister sorrow summer tem per tissue tunnel vesse1 walnut
attack candle dollar horror jungle kettle leader manner market matter needle office paddle pillar saddle spider supper tennis travel valley
Reduced S troop Interference - 1 3 8
Appendix B 1 : Participant Consent Form
1 have volunteered to take part in a study conducted by Mike Dodd in the Psychology Department, under the supervision of Dr. Colin MacLeod. 1 understand that my participation will involve attending on session of 30 minutes or less, the time to be arranged by mutual consent. 1 have been informed that for my participation in this experiment, I will receive '/r credit.
I understand that, in this experiment. 1 will be presented with a number of words and will be asked to either identiS, their colour of ink, or read them aloud (instructions will differ for different sections of the experiment). 1 have received instructions and have had the opportunity to ask questions and have had them answered before beginning. 1 understand. too, that I will be given some practice or farniliarization with the task before the actual expenment begins.
1 understand that the results of this study are not expected to be of direct benefit to me. It is hoped, however, that the information obtained will lead to a better understanding of colour naming. It has been made clear to me that, for the purposes of the experiment and in any subsequent reports, I will be identified by arbitrary subject number only.
I understand that following my participation I will be given a more detailed account as to the purpose of this study. I consent to participate in this project with the understanding that I may withdraw fieely and without consequence at any time.
Name Date Signature
Reduced Stroop Interference -1 39
Appendix 82: Participant Feedback Sheet
First and foremost. thank you very much for your participation in the present expenment. It has been very helpful to the research process.
The experiment that you just took part in has to do with a phenomenon known as the Stroop effect (which you have either heard of or will leam as pan of your Introductory Psychology class). The Stroop effect was discovered in 1935 and has received a great deal of attention fiom psychological researchers over the last half century. The basic idea behind the Stroop effect is that if 1 were to present you with a list of colour words and asked you to read them, you could do this quite easily. If. however. I gave you a list of colour words which 1 coloured in incongruent ink colours (e.g. the word RED in the colour blue) and asked you to identify these ink colours, you would have a difficuit time doing this. Even though you are supposed to name the ink colour and ignore the colour word. this is very difficult to do. In essence. the colour word is read "automatically" and it interferes with the colour naming response.
The Stroop effect has long been thought of as key evidence that when we encounter words. we automatically read them. Recently, however, a group of researchers have suggested that the Stroop effect can be eliminated by colounng a single letter of a colour word. rather than fûlly colounng the word. These researchers have then suggested that we do not necessarily read words automatically. and that theones of automaticity are too strong. We believe, however. that these researchers have not actually eliminated the Stroop effect so much as they have created the illusion of eliminating this effect through the use of questionable research rnatenals. These researchers have not demonstrated that colounng a single letter prevents people From automatically reading a word that is presented to them. Thus. the purpose of my research has been to more fully examine how people process words when they appear with only a single letter coloured. You have just participated in the 2nd and 3d portions of my research. The first ponion was a replication of a previous study and was completed last tem. Again. thank you very much for al1 your help.
Reduced Stroop Interference - 140
Appendix C: Written On-Screen Instructions For Subjects In Experiment I
Thanks for helping us by taking part in this experiment. Please read the following instructions carefully so you know what you are going to do. Your task throughout this experiment is to identify the colours in which you see words and nonwords pnnted as fast as you can, avoiding rnistakes. To identify each item's colour, you should just press the button for that colour. Remember to go as quickly as you can without making mistakes. You will be identifjmg the colours of about 200 items; don't worry, it actually won't take very long. There are only four colours: red, blue, green, and yellow. Sometimes the whole item will be printed in colour. and sometimes only one letter will be printed in colour (in that case, the remaining letters will be pnnted in white). Here are two examples:
green yellow
You would respond by pressing the 'red' button to each of these."
The words will be the 4 colour words: red, blue, green, and yellow. There will also be four nonwords: ret, blat, grend, and yenile. Your job is to ignore the written item, whether it's a word or a nonword, and simply identify the colour in which it is printed as fast as you can. Please don't try to read the item; that will just slow you down. We want to see how good you are at ignoring the printed items. Before we begin the 200 items, there will be a short set of 12 practice items so you can get the 'feel' of the task. There will also be a short rest afler 100 items. As well. aeer you identify the colour of each item, you will see a row of stars (******) on the screen, to let you know that the next item will appear in about half a second. Dunng the experiment, please be sure to press only one button for each item. If you have any questions. please ask them now or during practice; we cannot intempt the actual experimental items.
Press the space bar to begin practice.
A i the corrcltrsioti of lhe practice session, the foilowirig t r x ~ apprmd:
Okay, that's how the experiment will work. The only difference now will be that there will be 200 items instead of 13. If you have any funher questions, please ask them now because 1 cannot answer them once the experiment has begun.
Press the space bar to begin this part of the experiment.
Reduced Stroop Interference - 14 1
Appendix D: Wntten On-Screen Instructions For Subjects In Experiment 2a
Thanks for helping us by taking part in this experiment. Please read the following instructions carefblly so you know what you are going to do. Your task throughout this experiment is to identify the colours in which you see words printed as fast as you can, avoiding mistakes. To identify each item's colour, you should just press the button for that colour. Remember to go as quickly as you can without making mistakes. You will be identiwng the colours of about 30 items. There are only four colours: red, blue, yellow, and green. Sometimes the whole item will be printed in colour, and sometimes only one letter will be printed in colour (in that case, the remaining letters will be printed in white). Here are two examples:
i!iinh copper
You would respond by pressing the 'red' button to each of these.
Each trial will consist of a different English word. Your job is to ignore the written item. and sirnply name the colour in which it is printed as fast as you can. Please don't try to read the item: that will just slow you down. We want to see how good you are at ignoring the printed items. Before we begin the 30 items, there will be a short set of 12 practice items so you can get the 'feel' of the task. M e r you name the colour of each item. you will see a row of stars (* * * ** * ) on the screen to let you know that the next item will appear in about half a second. During the expenment, please be sure to press only one button for each item. If you have any questions, please ask them now or during practice; we cannot intempt the actual experimental items.
Press the space bar to begin practice.
At the cortclz~sion of the practice session, the foliowbg tex! appeared:
Okay, that's how the experiment will work. The only difference now is that there will be 30 items instead of 12. If you have any funher questions, please ask them now because 1 cannot answer them once the experiment has begun.
Press the space bar to begin this part of the experiment.
AI the conclzision of the Stroop rnsk, the followir~g text npprared:
You will now be presented with 64 words. some of which appeared dunng the colour narning task and others of which did not appear. Your job will be to identie the words that you DID see in colour (either al1 in colour by pressing the YES button. For words that you did NOT see in colour (new words), you should press the NO button. Even if you are not positive, but you think you saw a word in colour before, you should press the YES button. Remember to try to be as accurate as you can. If you have any further questions, please ask thern now because I cannot answer them once the experiment has begun. 1 will now show you which buttons to use for YES and NO.
Reduced Stroop Interference - 142
Appendix E: Wntten On-Screen Instructions For Experhent 2b
Thanks for helping us by taking part in this experiment. Please read the following instructions carefully so you know what you are going to do. Your task throughout this experiment is simply to read the words which are presented to you as fast as you can. avoiding mistakes. To identiQ each item you should just read that word aloud into the microphone. Please read loud enough so that the microphone picks up your response. Remember to go as quickly as you can without making mistakes. You will be reading about 60 words. These words will appear in one of four colours: red, blue, yellow, or green. Sometimes the whole word will be printed in colour, and sometimes only one letter will be pnnted in colour (in that case, the remaining letters will be printed in white). Here are two examples:"
t hi tiL cop per
Your task is to read the word out loud as quickly as you can. Please ignore the colour and simply read the word aloud.
Before we begin the 60 items, there will be a shon set of 12 practice items so you can get the 'feel' of the task. After you read each item, you will see a row of stars (******) on the screen to let you know that the next item will appear in about half a second. If you have any questions. please ask them now or during practice; we cannot intempt the actual experimental items.
At the concli<siotr of the practice session, the foi~owitzg trxt appemed:
Okay, that's how the experiment will work. The only difference now is that there will be 60 items instead of 12. If you have any further questions, please ask them now because 1 cannot answer them once the experirnent has begun.
Reduced Stroop Interference - 143
Appendix F: Wntten On-Screen Instmctions For Expenment 3
Thanks for helping us by taking part in this experiment. Please read the following instructions carefully so you know what you are going to do. Your task throughout this experiment is to identifL the colours in which you see rows of asterisks printed as fast as you can, avoiding rnistakes. To identify each item's colour, you should just press the bunon for that colour. Remember to go as quickly as you can without making rnistakes. You will be identi*ng the colours of about 60 items. There are only four colours: red, blue, yellow. and green. Sometimes the whole item will be printed in colour, and sometimes only one astensk will be pnnted in colour (in that case, the remaining asterisks will be printed in white). Here are two examp les:
You would respond by pressing the 'red' button to each of these.
Here are the buttons that you will be using to respond to the colour of the pnnted items:
If you see the colour red. please press z on the keyboard If you see the colour blue. please press x on the keyboard If you see the colour yellow, please press . on the keyboard If you see the colour green, please press I on the keyboard
Please place one hand on each side of the keyboard so that you may use your lefi hand (normally your rniddle and index fingers) to press the "z" and "x" keys, and your right hand (again. your index and middle fingers) to press the "." and "/" keys. While volunteers usually use their index and rniddle fingers, feel fiee to use your middle and ring fingers if you are more comfonable doing so. Before we begin the 60 items, there will be a short set of 24 practice items so you can get the 'feel' of the task. M e r you name the colour of each item, you will see a row of dashes (-- ----) on the screen to let you know that the next item will appear in about half a second.
Dunng the experiment, please be sure to press only one button for each item. If you have any questions, please ask them now or during practice; we cannot intempt the actual experiment al items.
A t the cor~clicsio~~ of the practice sesszor~, the foilowb~g text apprared:
Okay, that's how the experiment will work. The only difference now is that there will be 60 items instead of 24. If you have any further questions, please ask them now because we cannot answer them once the expenment has begun.
Reduced Stroop Interference - 144
Appendix G: Summary Table for a 2 x 2 Within Subjects ANOVA With Word Type (W) and Colouring Type (C) as the Independent Variables and Colour Naming Times as the Dependent Variable
Source df MS F
W 1
Error 34
C 1
Error 34
w x c 1
Error 34
Note: * denotes p < .10; ** denotes p 5 .OS; ***denotes p 5 .O 1
Reduced Stroop Interference - 145
Appendix H: Surnmary Table for a 2 x 2 Within Subjects ANOVA With Word Type (W) and Colouring Type (C) as the Independent Variables and Error Rates as the Dependent Variable
Source d f MS
W 1 0.000 1 O. 135
Error 34 0.0009
C 1 0.00 18 3.406"
Error 34 0.0005
W x C 1 0.0008 1 .O63
Error 34 0.0007
Note: * denotes p < .IO; ** denotes p 5 .05; ***denotes p < .O 1
Reduced Stroop Interference - 146
Appendix 1 I : Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Colour Naming Times as the Dependent Variable (For Control Words Only).
Source SS d f MS F
Letter 547 14.6 1 5 10952.92
Error 13 70665 170 8062.73
Total 1425379.6 1 175
Note: * denotes p ( .10; ** denotes p 5 .05; ***denotes p 5 . O 1
Reduced Stroop Interference - 147
Appendix 12: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Colour Naming Times as the Dependent Variable (For Incongment Colour Words Only).
Source SS d f MS F
Total 1917673.59 175
Note: * denotes p < .IO; ** denotes p 5 .OS; ***denotes p 5 -01
Reduced Stroop Interference - 148
Appendix J I : Surnmary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Error Rates as the Dependent Variable (For Incongruent Colour Words Only).
Source SS d f MS
Letter 0.0557 5 0.01 1 1
Error 1.2000 170 0.0070
Total 1.2557 175
Note: * denotes p 5 .IO; ** denotes p < .05; ***denotes p 5 .O 1
Reduced Stroop Interference - 149
Appendix J2: Sumrnary Table for a One Way Within Subjects ANOVA With Letter Position as the lndependent Variable and Error Rates as the Dependent Variable (For Control Words Only).
Source SS d f MS F
Letter
Error
Total
Note: * denotes p 5 -10; ** denotes p 5 .05; ***denotes p 5 .O 1
Reduced Stroop Interference - 150
Appendix 53: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Distractors With the First Letter Coloured Only).
Source SS df MS
Word 0.000 1 1 0.000 1
Error O. 1770 34 0.0052
Total 0.1771 35
Note: * denotes p 5 .IO; ** denotes p < .Os; ***denotes p 5 .O 1
Reduced Stroop Interference - 1 5 1
Appendix J4: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Distractors With the Second Letter Coloured Only).
Source SS d f MS
Word 0.001 1 1 0.001 1
Error O. 1530 34 0.0045
Tot al O. 153 1 35
Note: * denotes p 5.10; ** denotes p < .05; ***denotes p < .O1
Reduced Stroop Interference - 152
Appendix 55: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Distractors With the Third Letter Coloured Only).
Source SS d f MS F
Word O. 0266 1 0.0266 8.226***
Error O, 1 IO0 34 0.0324
Total O. 1365 35
Note: * denoies p 5 .IO; ** denotes p 5 .OS; ***denotes p < -01
Reduced Stroop Interference - 153
Appendix 16: Surnrnary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Words With the Fourth Letter Coloured Only).
Source SS d f MS F
Word 0.00 17 1 0.00 17 0.380
Error O. 1420 34 O. 0042
Total O. 1437 35
Note: * denotes p 5 .IO: ** denotes p 5 -05; ***denotes p 5 .O1
Reduced Stroop Interference - 154
-4ppendix 57: Surnrnary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Distractors With the Fifth Letter Coloured Only).
Source SS d f MS F
Word 0.0022 1 0.0022 O. 195
Error 0.3980 34 0.01 17
Total 0.4002 35
Note: * denotes p 5 .10; ** denotes p < .05; ***denotes p 5 .O 1
Reduced S troop Interference - 1 5 5
Appendix 58: Sumrnary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Error Rates as the Dependent Variable (For Distractors With the Sixth Letter Coloured Only).
Source SS d f MS F
Word 0.0036 1 0.0036 1 .O00
Error O. 12 10 34 0.0036
Totai O. 1246 35
Note: * denotes p 5.10; ** denotes p 5 .05; ***denotes p 5 -01
Reduced S troop Interference - 1 5 6
Appendix K1: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Narning Times as the Dependent Variable Fo r Words With the First Letter Coloured Ody).
Source SS d f MS F
Word 21.73 I 21.73 O. 004
Error 206670.8 34 6078.55
Total 206692.53 35
Note: * denotes p 5 .IO; ** denotes p < .05; ***denotes p < .O 1
Reduced Stroop Interference - 157
Appendix K2: Sumrnary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Narning Times as the Dependent Variable (For Words With the Second Letter Coloured Only).
Source SS d f MS F
Word 2366.4 1 1 2366.4 1 0.35
E rro r 332942.1 34 685 1.24
Tot al 235308.94 35
Note: * denores p 5 .IO; ** denotes p < .05; ***denotes p < .O I
Reduced Stroop Interference - 158
Appendix K3 : Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Naming Times as the Dependent Variable (For Words With the Third Letter Coloured Only).
Source SS d f MS
Word 46853. 16 1 46853.16
Error 149653 . 3 34 440 1.57
Total 196506.46 35
Note: * denotes p 5 -10; ** denotes p < .05; ***denotes p < .O 1
Reduced Stroop Interference - 159
Appendix K4: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Naming Times as the Dependent Variable (For Words With the Fourth Letter Coloured Only).
Source SS d f MS F
Word 17569.73 1 17569.73 3.46*
Total 190237.53 35
Note: * denotes p 5 .10; ** denotes p 5 .05; ***denotes p 5 .O1
Reduced Stroop Interference - 160
Appendix K5: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Naming Times as the Dependent Variable (For Words With the FiRh Letter Coloured Only).
Source SS d f MS F
Word 1536.9 1 1 1536.9 1 . 1 3
Error 404283.1 34 1 1890.68
Total 405820.0 1 35
- -
Note: * denotes p Ç .IO; ** denotes p < -05; ***denotes p 5 -01
Reduced Stroop Interference - 1 6 1
Appendix K6: Summary Table for a One Way Within Subjects ANOVA With Word Type as the Independent Variable and Colour Narning Times as the Dependent Variable (For Words With the Sixth Letter Coloured Only).
Source SS d f MS
Word 10.41 1 10.41
Enor 846905.1 34 24908.97
Total 846915.5 1 35
Note: * denotes p 5.10; *+ denotes p 5 -05; ***denotes p < .O1
Reduced Stroop Interference - 162
Appendix L: Summary Table for a One Way Within Subjects ANOVA With Colouring Type (Al1 Letters or One Letter) as the Independent Variable and Colour Naming Times as the Dependent Variable .
Source SS d f MS F
Colour 28087.12 1 28087.12 9.494***
Enor 97623.88 33 2958.30
Total 12571 1 34
Note: * denotes p 5 -10: ** denotes p 5 .05: ** *denotes p 5 .O 1
Reduced Stroop Interference - 163
Appendix M: Summary Table for a One Way Within Subjects N O V A With Letter Position as the Independent Variable and Colour Naming Times as the Dependent Variable.
Source SS d f MS F
Letter 282423.2 5 56484.63 2.173*
Total 457058 1.3 170
Note: * denotes p 5.10; * * denotes p 5 .05; **+denotes p 5 -01
Reduced Stroop Interference - 164
Appendix N: Summary Table for a One Way Within Subjects ANOVA With Colounng Type as the Independent Variable and Error Rates as the Dependent Variable .
Source SS df MS F
Colour 0.000 1 1 0.000 1 0.033
Error 0.060 1 33 0.00 18
Total 0.0602 34
Note: * denotes p 5 .10; ** denotes p 5 .OS; ***denotes p < .O1
Reduced Stroop Interference - 165
Appendix O: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Error Rates as the Dependent Variable
Source SS d f MS F
Letter
Error
Total
Note: * denotes p 5-10; ** denotes p 5 .05; ***denotes p < .O1
Reduced Stroop Interference - 166
Appendix RI: Summary Table for a One Way Within Subjects ANOVA With Word Type (Fully Coloured vs. Single-Letter-Coloured vs. Not Presented) as the Independent Variable and Recognition Rates as the Dependent
Variable.
Source SS d f MS F
Word 1 S860 2 0.7930
Error 0.9750 66 0.0 148
Total 2.5610 68
&te: * denotes p < .lO; ** denotes p 5 -05: ***denotes p 5 .O1
Reduced Stroop Interference - 167
Appendix R2: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Recognition Rates as the Dependent Variable.
Source SS d f MS F
Letter 0.6 180 5 O. 1240 I .O36
Note: * denotes p 5 .IO; ** denotes p 5 -05; ***denotes p 5 .O1
Reduced Stroop Interference - 168
Appendix S 1: Summary Table for a One Way Within Subjects ANOVA With Response Type (Fully Coloured Hits vs. Single-Letter-Coloured Hits vs. Unstudied False Aiarms) as the Independent Variable and Recognition Response Times as the Dependent Variable.
Source SS d f MS F
Word 407 196 2 203597.8 1.45
Error 92672 12 66 1404 12.3
Total 9674408 68
Note: * denotes p 5 -10; ** denotes p < .05; ***denotes p 5 .O1
Reduced Stroop Interference - 169
Appendix S2: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Recognition Response Times as the Dependent Variable.
Source SS d f MS
Letter 1661074 5 3322 14.8
Error 4530202 1 165 274557.7
Total 46963095 170
Note: * denotes p < - 1 O: * * denotes p 5 .05; ** *denotes p < .O 1
Reduced Stroop Interference - 170
Appendix T: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Recognition Response Times as the Dependent Variable.
Source SS d f MS F
Letter 1662943 5 332588.7 1.21
Error 45780190.5 165 274557.7
Total 47443 133.5 170
Note: * denotes p 5-10; ** denotes p < .OS; ***denotes p 5 .O1
Reduced Stroop Interference - 1 7 1
Appendix U: Summary Table for a One Way Within Subjects ANOVA With Colouring Type as the Independent Variable and Word Reading Times as the Dependent Variable.
Source SS d f MS F - -
Colour 1 169.47 1 1 169.47 2.767 (!)
Error 13945.53 24 422.59
'Total 151 15 25
Note: * denotes p 5 -10; ** denotes p < .05; ***denotes p < .O 1; ! actual p = . IO6
Reduced S troop Interference - 1 72
Appendix V: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Word Reading Times as the Dependent Variable.
Source SS d f MS F
Letter 20693.80 5 4138.76 3 . IO***
Error 220663.9 165 1337.36
Total 241357.7 170
Note: * denotes p 5.10; ** denotes p < .05; ***denotes p 5 .O1
Reduced Stroop Interference - 173
Appendix W 1 : Summary Table for a One Way Within Subjects ANOVA With Colounng Type as the Independent Variable and Colour Naming Times as the Dependent Variable (For Rows of Astensks).
Source SS d f MS F
Colour 4723,92 1 4723.92 7.9 1 ***
Enor 14348.48 24 597.84
Total 19072.4 25
Note: * denotes p 5 -10; ** denotes p 5 .05; ***denotes p < .O1
Reduced Stroop Interference - 174
Appendix W2: Surnmary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Colour Naming Times as the Dependent Variable (For Rows of Astensks).
Source SS d f MS F
Letter 59406.3 8 5 11881.28 1.65
Total 921752.88 125
Note: * denotes p < -10: ** denotes p 5 -05; ***denotes p 5 .O1
Reduced Stroop Interference - 175
Appendix XI : Summary Table for a One Way Within Subjects ANOVA With Colouring Type as the Independent Variable and Error Rates as the Dependent Variable (For Rows of Asterisks).
Source SS df MS F
Colour O. O007 1 0.0007
Error 0.0 138 24 0.0006
Total 0.0 145 25
Note: * denotes p 5 -10; ** denotes p 5 .OS: ***denotes p < 0 1
Reduced S troop Interference - 1 76
Appendix X2: Summary Table for a One Way Within Subjects ANOVA With Letter Position as the Independent Variable and Error Rates as the Dependent VanabIe (For Rows of Asterisks).
Source SS d f MS
Letter 0.0 167 5 0.0033
Error 0.3440 120 0.0029
Total 0.3607 125
Note: * denotes p < .IO; ** denotes p 5 .OS; ***denotes p < -01
Applicants for admission for Sept. 2001 (as of January 30.2001)
t u l a lsî&&R alh&&
Anderson, Rheanne Arsalidou, Marie Bayrami, Lisa Bebiroglu. Neda Bender, Danielle Bharadia, Vinay Birze. Arija Borch, Shannon Burney. Atiya Campos. Jennifer Cantanese, Dana Catanzaro. Anna Maria Chan, Kimberley Chard, Diana Chukwuemeka-aju ba, Gregory Coleman, Julie Cornier, Natalie Craig, Kristin D'Angelo. Francesca Duval. Cara Dyke, Danielle Eliav, Jasmine Fahy, Louise Favor, Stacey Fung, Francis Glenn. Julie Grant, Sabrina Harrison, Jererny Hemog, Ludmila Hitzig, Sandra Hopyan. Talar Huizinga. Carolyn lshmael. Tracy Jeansson. Vivian Kalpakis, Elaine-Marie Keay, Pamela Kemmotsu. Nobuko Kendall, Julia Knight. Melanie Krete, Oana Launeanu, Mihaela Leal, Elizabeth Loumbeva. Nadejda Luo, Lin MacDonald, Heather Mahler. Stephen Martin, Nicholas McCou brey. Gail McGillivray, Shannon McHugh, Tara Mclsaac. Caroline Mohebat. Emis Moradi. Farshad Niiya, Yu O'Connor. Charlene Orprecio. Jazmine Saelhof, Michael Sarkar, Christopher Semenya. Antoinette Sethian, Taline Shen. Ching-Ting Shen Sheppard. Michael Smith, Kathleen Soule. Michelle Spence, Men's Steinberg, Daniel Ta-Min, Rachelle TaIrni, Deborah Taylor. Chnstopher Telner, Jason Tirtabudi, Prisilia Tosco. Anna Maria Trottier. Kathryn
Devel PICICN Devel Devel SPA B&B SPA SPA Devel 688 SPA Devel 888 SPA B&B SPA SPA SPA PICICN SPA Devel Devel Devel SPA Devel Devel SPA SPA SPA Devel Ba8 SPA SPA PICICN Devel SPA SPA SPA SPA SPA Devel SPA SPA PICICN B&B SPA SPA PICICN SPA 888 SPA B&B PlCICN SPA B&B PICICN SPA SPA SPA SPA SPA SPA Devel Devel SPA SPA PICICN PICICN PICICN PICICN PICICN SPA SPA
SPA
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888 SPA
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Applicants for admission for Sept. 2001 (as of January 30.2001) dlarm lsuhuh aîc&Q
Vasilescu, Maria-Cristina Velasquez, Ana Vishram, Julie Wager. Brandon Walsh. Andrew Wareham, Stacey Weir, Kelly A. Wells, Elizabeth Np, Wan Hung Yuval. Linda
B&B Devel 888 6&B P/C/CN SPA SPA SPA PICICN SPA