Journal of Experimental Psychology:Learning, Memory, and Cognition1990, Vol. 16, No. 5, 760-771

Copyright 1990 by the American Psychological Association, Inc.O278-7393/9O/SO0.75

Controlling Stroop Interference:Evidence From a Bilingual Task

Joseph Tzelgov, Avishai Henik, and David LeiserDepartment of Behavioral Sciences

Ben Gurion University, Beer Sheva, Israel

Skilled performance is often associated with automaticity. Automatic processes are generallythought of as uncontrollable so that automaticity implies the lack of control. The Stroop color-naming task is one of the most cited examples of automaticity and uncontrollability of wordreading. This task is also employed extensively to investigate the structure of the bilingual lexicon.The present work employed a Hebrew-Arabic bilingual Stroop task in two separate experiments.To induce controlled processing, we varied the subjects' expectations regarding the written(irrelevant) color words. The Stroop interference effect was always present but subjects were ableto control (reduce) it in their native language but not in their second language. In addition, thepresumed structure of the bilingual lexicon seems to change in accordance with proficiency inthe second language. It is suggested that automaticity and control are both characteristics ofskilled performance with each of them reflecting a different aspect and each subserving a differentfunction of our cognitive system.

The present study addressed two related issues: a) automa-ticity and control, and b) the structure of the bilingual knowl-edge representation. To this end we employed a Stroop taskin a bilingual situation.

Automaticity and Control

Most theorists argue that automatic processes are effortless,unconscious, and involuntary (e.g., Hasher & Zacks, 1979;Posner, 1978; Shiffrin & Schneider, 1977). The involuntarynature of automaticity is reflected in several properties: au-tomatic processes occur without intention; when activatedthey run to completion; their operation cannot be fully sup-pressed, and their products are hard to ignore (Hasher &Zacks, 1979; Posner & Snyder, 1975; Shiffrin & Schneider,1977; Zbrodoff & Logan, 1986). This implies that automaticprocesses are uncontrollable. Indeed, automaticity and con-trol are suggested as two opposing concepts (Schneider, Du-mais & Shiffrin, 1984). The characteristics of automaticityhave been reserved for highly skilled performance, the originof which is usually related to heredity or practice (Hasher &Zacks, 1979; Shiffrin & Schneider, 1977). According toHasher and Zacks (1979), large amounts of practice result inthe development of automatic processes, which in turn func-tion to prevent subcomponents of complex skills from over-

We are grateful to Osnat Milman and Limor Kaplan for coordi-nating the project and to Jacqueline Berger for her comments. Wealso thank Gordon Logan, Colin MacLeod and three anonymousreviewers for their valuable comments and suggestions. They are notto be blamed for any shortcomings of this article. Earlier versions ofthis article were presented at the 21st Scientific Meeting of the IsraeliPsychological Association in March 1987 and the 6th AustralianLanguage and Speech Conference in August 1988.

Correspondence concerning this article should be addressed toJoseph Tzelgov, Department of Behavioral Sciences, Ben-GurionUniversity of the Negev, Beer-Sheva, Israel 84105.

loading our limited-capacity system. The subcomponents ofskilled performance, which become automatic with practice,serve the skilled performer in being executed effortlessly andwithout the need to be monitored closely as performanceproceeds. The equivalence between proficiency and automa-ticity is also implied in studies of the bilinguals' lexicon. Forexample, Magiste (1984) suggested that the amount of inter-ference from a language is directly related to experience inthat language.

In contrast, it has often been suggested that skill involvescontrol (see Logan, 1985, for a discussion of this point). Weusually think about skill or mastery as manifested in ease ofmanipulation, or in the ability to accommodate to situationaldemands and constraints. According to this point of view,skill would also be evidenced in an ability to withhold certainprocesses. This has been demonstrated with skilled typists(Logan, 1982) and adult speakers (Levelt, 1983). Consideringthese conclusions together reveals that current theorizing onskill and automaticity is inconsistent. The development of askill involves both automaticity and control. As skill develops,the performer learns to control the components of the skill.However, at the same time various processes become auto-matized and less controlled to the point of being executedinvoluntarily or autonomously (Zbrodoff & Logan, 1986).Logan (1985) has recently discussed this issue and suggestedthat the general belief that automaticity and control areopposites may be overstated. Posner (1978) suggested onesolution when discussing the reflexive nature of eye move-ments: he suggested that the eye movement system might beviewed as one that requires minimal attention but which canbe brought under conscious control if so desired. However,this solution cannot apply to processes that are carried outautomatically and at the same time show a certain level ofcontrol.

One of the most cited examples for automaticity and un-controllability is the Stroop effect (Stroop, 1935). In thissituation, subjects are asked to name the ink color of a word

760

BILINGUAL STROOP CONTROL 761

and refrain from reading the word itself (e.g., when presentedwith the word GREEN written in red they are supposed toanswer "red"). Ink color naming is faster when the twodimensions of the stimulus are congruent (e.g., GREEN^ writ-ten in green) than when they are incongruent (e.g., GREENwritten in red). That is, the irrelevant, to-be-ignored dimen-sion interferes with processing the relevant dimension. Wordreading is initiated without intention and in spite of thesubjects' attempts to suppress it. This pattern of results issuggested as an example of the automaticity of reading. Ac-cordingly, the Stroop effect should increase as reading expe-rience increases. In the Stroop paradigm, control means theability to inhibit the irrelevant reading process. Develop-mental studies show that the effect increases and then de-creases as age and reading experience increase (Schiller, 1966;Schadler & Thissen, 1981). The decrease of the effect is notpredicted by the notion of automaticity. However, it does fitrather nicely with the suggestion that improvement in skillimplies control. Thus, it may be that the Stroop effect evi-denced in the performance of children shows automaticityand control simultaneously: automaticity is shown by thecolor name interference, whereas control is suggested by thereduction of this effect with the increase in reading experience.

There are some hints in the literature that subjects canmodulate the activation of concepts (e.g., Neely, 1977). Someexperiments investigating control in Stroop situations havebeen reported (Logan, 1980; Logan & Zbrodoff, 1979). How-ever, the evidence is equivocal. While Stroop interferenceseems to be sensitive to expectations when two colors areemployed, it is not affected by expectations when the numberof colors increases (Logan, Zbrodoff & Williamson, 1984).Our study attempts to unravel effects of controlled processingin a bilingual Stroop situation.

The Bilingual Lexicon

Collins and Loftus (1975) suggested a two-level model ofknowledge representation. They distinguished between se-mantic and lexical levels of representation. Concepts arerepresented at the semantic level, usually referred to as the"semantic network," whereas their names are represented atthe lexical level. We will refer to this level of representationas the internal "dictionary".1

The Stroop effect implies automatic activation of the colorname in the semantic network. The bilingual Stroop task hasbeen employed extensively in studies aimed at investigatingthe structure of the bilingual's knowledge representation.These research efforts have documented the existence of abetween-language Stroop interference (e.g., Dalrymple-Al-ford, 1968; Dyer, 1971; Fang, Tzeng, & Alva, 1981; Kiyak,1982; Preston & Lambert, 1969). Most investigators reportthat the within-language interference is larger than the be-tween-language interference (Dyer, 1971; Kiyak, 1982; Pres-ton & Lambert, 1969, but see Ehri & Ryan, 1980). Recentstudies have indicated that the between- as well as the within-language interference is determined by language proficiency(Magiste, 1984, 1986).

The difference between the within-language and the be-tween-language effect suggests that the internal lexicon is

organized in terms of language-specific units. Several authorshave discussed such a structure of the lexicon (Kirsner, Smith,Lockhart, King, & Jain, 1984; Potter, So, Von Eckardt, &Feldman, 1984). According to this approach, words from thesame language are closer to each other in the internal lexiconthan words from different languages. Bilingual versions of thebasic structure suggested by Collins and Loftus (1975) thatassume language-specific "dictionaries" and a common se-mantic representation have recently been suggested by severalinvestigators (Chen & Leung, 1989; Gerard & Scarborough,1989; Groot & Nas, 1989; Grainger & Beauvillain, 1989;Tzelgov & Henik, 1989). Potter et al. (1984) discussed twohypotheses about the relations between the language-specificlexicons:

1. Concept mediation hypothesis: There are no direct con-nections between the parallel words in the different languages.Parallel words (from the different languages) are connectedvia an amodal conceptual system (i.e., the semantic level ofrepresentation).

2. Word association hypothesis: Here, comprehension of aword is always mediated by access to units of the moreproficient language. That is, access to and from a word in theless proficient language is always mediated by the activationof the parallel word in the more proficient language.

Studies that show a larger within- than between-languageinterference effects are consistent with the concept mediationhypothesis. When the task involves two languages (i.e., be-tween-language condition), activation has to spread from onearea of the lexicon to another, via the amodal system, in orderto create an interference effect. In contrast, when the taskinvolves only one language (i.e., within-language condition),there is no need for the activation to spread via the amodalsystem to create an interference. Studies that present theinfluence of proficiency on the size of the interference effectssupport the word association hypothesis. For example, Mag-iste (1984) reported that the different language interferenceeffect increases with proficiency in a given language.

Chen and Ho (1986) investigated the development ofStroop interference in Chinese-English bilinguals. They foundthat at the first stages of learning the second language (Eng-lish), the interference created by the first language (Chinese)is larger than the interference created by the second language.This is true for both the different language and same languageconditions. However, as experience with the second languageincreases, the same language interference effect becomesgreater than the different language interference effect in thatlanguage. Chen and Ho proposed a mixed model of languagerepresentation: They suggested that Chinese-English bilin-guals use lexical associations to start with, but these associa-tions are gradually replaced by concept mediation links withthe increase of the proficiency in the second language. Chen

' Collins and Loftus (1975) refer to the representation of concepts'names as the "lexical network" (see p. 413). In contrast, in thebilingual literature the term "lexicon" is used to describe the internalrepresentation of knowledge in general. We use the term lexicon in asimilar way. We use the term "dictionary" (which is also used byCollins & Loftus, 1975) to denote the representation of conceptnames.

762 J. TZELGOV, A. HENIK, AND D. LEISTER

and Ho's (1986) suggestions imply an interdependence be-tween proficiency and the structure of the lexicon. This struc-ture would change as subjects become more skilled with anew language.

We have claimed that the ability to control language proc-essing is reflected in a decline in Stroop interference in devel-opmental studies. It seems that the first stages of languageacquisition reflect the development of the automatic compo-nent by an increased Stroop interference effect. In the moreadvanced stages, control is reflected by the decline of Stroopinterference. It is possible that these processes, automatizationon the one hand and increased control on the other, play amajor role in changing the pattern of the between-languagesand the within-language Stroop interference. For example,improved ability to control (i.e., inhibit) reading of the firstlanguage contributes to a reduction in the between-languageeffect of the first language. At the same time, the increasedautomatization in reading the second language contributes toan increase in the interference of the second language. Thus,in an advanced stage of reading proficiency the amount ofthe interference reflects both automatization and control proc-esses. Most students of the field relate a major role to auto-matizaion. The present study attempts to unravel the roleplayed by the control processes in bilinguals' reading.

Experiment 1

We exposed Arabic-Hebrew bilinguals to a bilingual ver-sion of the Stroop task and manipulated their expectationsregarding the written language. If the subject has no control,or cannot suppress the reading of the irrelevant color wordeven when it is expected, Stroop interference would be insen-sitive to the proportion of words in a given language. If thesubject can control his or her reading, Stroop interference inthe expected language should diminish relative to the, inter-ference in the same language when unexpected.! However,: itmay be that the relations between expectations andStooopinterference are more complicated than this. *As« suggestedabove, the notion of skill implies a close relationship betweenproficiency and control. Such a relationship between skill andcontrol implies that subjects should be better at controllingthe better known language. This should contribute to a re-duction in Stroop interference in that language when expectedas compared to the language unexpected condition, whereasexpectation may not affect Stroop interference in the lessknown language. Native speakers of Arabic who were quiteproficient in Hebrew participated in the experiment.

In the present context, control can be exerted by inhibitionof the irrelevant reading processes. This should be evidencedin a reduction of Stroop interference. Because the subjectswere more proficient in Arabic, one may expect such areduction for Arabic. It is not clear whether the same appliesalso to Hebrew. In addition, to the extent that the subjectswere proficient in Hebrew, we may expect that Stroop inter-ference in the within-language conditions will be larger thanin the between-language conditions. This would support theconcept mediation hypothesis.

Suppose that the present subjects could control only Arabic,whereas Hebrew was processed automatically and without

control. When the subjects expect Arabic stimuli (i.e., when80% of the stimuli are Arabic words) they may be able toinhibit the irrelevant reading process. This would reduceStroop interference relative to the unexpected condition forArabic written stimuli. Would this reduction be larger in thebetween-languages (i.e., response language Hebrew) than inthe within-language (i.e., response language Arabic) condi-tion? In the between-languages condition one has to inhibitor attenuate one whole system (i.e., Arabic), whereas in thewithin-language condition one has to inhibit processes withina system currently employed (i.e., inhibit reading Arabic whileresponding in Arabic). This pattern is not expected for thesecond language that the subjects cannot control. Such apattern of results should be reflected in an interaction involv-ing all four variables. In contrast, a lack of a fourth-orderinteraction would be consistent with MacNamara and Kush-nir's (1971) assertion about independent activation mecha-nisms for input (stimulus) and for output (response) languageprocessing.

Method

Subjects. Sixteen Arabic-Hebrew bilingual students of Arabicorigin participated in the experiment. Arabic was the native languageof all the subjects. All of them began to study Hebrew in elementaryschool and thus studied Hebrew for at least twelve years. They werequite proficient in Hebrew, but knew Arabic better. They spoke onlyArabic at home and both Hebrew and Arabic with friends. Outsideof the home, they used mainly Hebrew for everyday interaction.Participation in the experiment was in partial fulfillment of courserequirements or for payment.

Stimuli and apparatus. Five colors were employed in the experi-ment: red, green, blue, yellow, and black. The names of these colorsconsist of four-letter words, in both Hebrew and Arabic. There is nophonetic similarity betweeni Hebrew and Arabic for the color namesemployed. Hebrew and Arabic are both written from right to left, butuse different alphabets. The color names were written on white cards.Each word encompassed a rectangle of 30 x 8 mm centered at themiddle of the card. The stimuli were presented 80 cm away from thesubjects' eyes.

The apparatus consisted of a Gerbrand's Harvard 3-field tachisto-scope, connected to a voice operated relay and a Monsanto HT 8510countertimer.

Design. There were four experimental sessions which were atleast three days apart from each other. In two sessions subjects wereasked to respond in Hebrew and in two in Arabic. In one of tht twosessions Hebrew was more frequent (i.e., 80% of the words werewritten in Hebrew and 20% in Arabic) and in the other Arabic was

; frequent (i.e., 80% of the words were written in Arabic and: in Hebrew). Color-word congruency was manipulated within

session; Each session was composed of one block of 50 trials that waspresented twice. Forty trials in the block were written in the morefrequent language and 10 in the less frequent language. Half of thetrials within each block were congruent and half were incongruent.This arrangement resulted in at least 10 trials in each experimentalcondition. We decided to limit each session to 100 trials to avoidboredom effects, especially in the last two sessions of the experiment.

The 20 incongruent stimuli in the frequent language were createdby printing each of the five color names in four different color inks.The 20 congruent stimuli were created by printing each of the fivecolor names in its color ink four times. The ten stimuli of the lessfrequent language consisted of five congruent and five incongruent

BILINGUAL STROOP CONTROL 763

stimuli. Each group of five stimuli consisted of all five color namesand color inks. For each session the five incongruent trials wereselected out of the twenty possible stimuli. Each session had a differentset of such five stimuli so that the twenty possible stimuli werepresented in the four sessions.

To recapitulate, response language and frequent language weremanipulated between sessions, whereas color-word congruency andstimulus language were manipulated within session. All variableswere manipulated within subjects. Hence, this is a four-way repeatedmeasures design. The experiment is composed of 16 conditions: 2response languages (Hebrew vs. Arabic) x 2 levels of language fre-quency (80% Hebrew vs. 80% Arabic) x 2 congruency levels (con-gruent vs. incongruent) x 2 stimulus languages (word written inHebrew vs. word written in Arabic).

Procedure. Each subject participated in four sessions. Each ses-sion was homogeneous with respect to the response language. Therewere four different sessions according to the response and frequentlanguage conditions. Order of sessions was counterbalanced acrosssubjects by applying a Latin square arrangement. Thus, there werefour groups of subjects according to the four possible orders ofsessions. The trials in the block were randomly ordered and presentedto each subject either from the first to the 50th or vice versa. Asmentioned before, each block was presented twice within each session.

The task was explained to the subjects at the beginning of eachsession. They were asked to name the ink color and ignore the writtenword. They were asked to respond as fast as possible. Each sessionwas preceded by an explanation of its language structure (i.e., thefrequency relations between stimuli in the two languages). A sessionbegan with a practice block often trials, designed in the same way asthe experimental block.

Each trial started with a fixation point (a black cross on a whitebackground) that was on for 300 ms and that was replaced by a 200-ms blank (dark field) interval. The color word appeared at the end ofthe interval and stayed on until the subject's naming response. Thesubject's response stopped the timer and eliminated the stimulus.

Results

For each subject in each condition the median reactiontime (RT) of the correct responses was calculated.2 Thesemedians were subjected to a four-way repeated measuresanalysis of variance. Means and standard deviations of themedian reaction times in the various conditions of Experi-ment 1 are presented in Table 1.

Congruent ink colors were named faster than incongruentstimuli, F(\, 15) = 176.35, p < .001. This interference effectdepended on the different language and same language con-ditions, resulting in a significant triple interaction amongstimulus language, response language, and congruency, F(l,15) = 37.26, p < .005. This interaction appears in Table 2.

As indicated in Table 2, Stroop interference was muchlarger when the stimulus and the response languages matchedthan when they mismatched. The two simple interactioneffects, between congruency and stimulus language, were sig-nificant, both when the subjects responded in Hebrew, F(l,15) = 59.55, p < .001, and when they responded in Arabic,F(l, 15) = 11.86, p < .01. Further analyses of simple maineffects indicated that there were significant congruency effectsin the different language conditions, F(l, 15) = 54.46, p <.001, wherr. subjects responded in Hebrew and the words werewritten in Arabic; F(l, 15) = 27.69, p < .001, when subjectsresponded in Arabic and the words were written in Hebrew.

There were significant congruency effects in the same lan-guage conditions also, F([, 15) = 127.04, p < .001, forHebrew; F(l, 15) = 74.06, p< .001, for Arabic.

The congruency effect was also dependent on the corre-spondence between the stimulus language and the frequentlanguage. This was indicated by the significant triple interac-tion among these variables, F(l, 15) = 8.53, p < .01. Therelevant means appear in Table 3.

For the Hebrew written stimuli there was no significantcongruency by frequent language interaction [F < 1]. Thecongruency effect, across the two frequent language condi-tions, was very clear, F(l, 15) = 240.49, p < .001. For theArabic written stimuli, congruency interacted with frequentlanguage, F(l, 15) = 6.66, p < .01. This interaction wasreflected in a reduction of the interference effect when Arabicwas frequent (76 ms) relative to the condition in which Arabicwas infrequent (i.e., Hebrew was the frequent language, 121ms). Note, however, that the congruency effect was significantboth when Hebrew was frequent, F(l, 15) = 65.01, p < .001and when it was infrequent, F(l, 15) = 38.07, p < .001.

The interaction between frequent language and responselanguage (across congruency) was significant F(l, 15) =106.55, p < .001. When most of the stimuli were written inArabic the response language did not make any difference, F< 1. When the majority of the stimuli were written in Hebrew,responses in Arabic were 88 ms faster than responses inHebrew, F(l, 15) = 21.31, p< .001.

Stimulus language also interacted with response language,F(l, 15) = 17.85, p< .001, and with frequent language, F(l,15) = 45.57, p < .001. These effects, however, appeared alsoas part of higher order interactions and therefore were notanalyzed any further.

Discussion

As expected, we found a within-language and a between-languages Stroop interference effect. Furthermore, as in mostsimilar experiments (e.g., Fang, Tzeng, & Alva, 1981), thebetween-languages effects were smaller. The two within-lan-guage Stroop effects were about the same size, and the samefindings held for the between-languages conditions. Arabicwas our subjects' first language, and they reported higherproficiency in Arabic than in Hebrew. ,Yet, it seems that thebetween- and the within-languages Stroop interference didnot reveal Arabic dominance. This is consistent with thesubjects' high proficiency in Hebrew. This pattern of resultssupports the concept mediation hypothesis (Chen & Ho, 1986;Chen & Leung, 1989; Potter et al., 1984).

2 Subjects made about 2% errors. Almost all errors were color-naming errors. In a few cases, subjects made response language errors(i.e;, responded in a wrong language). It should also be noted that ina "non-frequent language" condition, an error rate of 1 % was equiv-alent to one trial. The same rate of errors in a "frequent-languagecondition" was equivalent to four trials. It follows that the standarderrors are different in the frequent and the infrequent conditions.Therefore, after verifying that there was no indication for a speed-accuracy tradeoff in our data, we focused on the reaction times.

764 J. TZELGOV, A. HENIK, AND D. LEISTER

Table 1Means (in Milliseconds) and Standard Deviations in the Experimental Conditions ofExperiment 1

Frequent language: Hebrew Frequent language: Arabic

Stimuluslanguage:Hebrew

Stimuluslanguage:

Arabic

Stimuluslanguage:Hebrew

Stimuluslanguage:

Arabic

Statistic

MSD

MSD

C

72484

70684

I

87794

77692

C

82493

66295

I

Response897110

Response829144

C

language:718

94

language:805113

I

Hebrew882117

Arabic885120

C

75985

71890

I

80891

821132

Note. C and I represent congruent and incongruent conditions, respectively.

Is there any evidence for controlled processing? In theintroduction, we suggested that control may be induced byexpectations (i.e., the frequent language variable). We founda similar Stroop interference for stimuli written in Hebrewregardless of their expectancy level. That is, even though oncertain sessions the subjects knew that the next stimulus wouldprobably be written in Hebrew, they could not suppressreading the irrelevant color name. In contrast, expectationinfluenced the size of the interference effect of color nameswritten in Arabic. The knowledge that, on certain sessions,the next stimulus would probably be written in Arabic didenable the subjects to reduce the amount of interference.

In the case of Hebrew written stimuli the Stroop effect wasinsensitive to expectations. However, expectations did affectthe processing of Hebrew written stimuli; when such stimuliwere expected they were processed faster than when unex-pected. This effect was not dependent on congruency rela-tions.

We would like to claim that the reduction in the Stroopeffect found in the experiment reflects control processes.Therefore, it is important to analyze how the decrease in theinterference effect is accomplished. The basic two conditionsused in the original Stroop task (Stroop, 1935) were theincongruent condition (e.g., BLUE written in red) and a

Table 2Mean Reaction Times in Experiment 1 (in Milliseconds) asa Function of Stimulus Language, Response Language, andColor Name Congruency

ResponselanguageHebrewArabic

Cong.721791

Stimulus language

Hebrew

Incong. I.E.880 159852 61

Cong.757689

Arabic

Incong.830825

I.E.73

136

neutral condition (e.g., XXXX written in red). Another ex-perimental condition frequently used in Stroop tasks is thecongruent condition (e.g., RED written in red). The differencebetween the incongruent and the neutral trials is usuallyreferred to as "inhibition," whereas the difference betweenthe neutral and the congruent trials is referred to as "facilita-tion." In the reported experiment we used an incongruentand a congruent condition.3 The Stroop effect, or "interfer-ence effect," we are discussing is therefore the sum of thecomponents of facilitation and inhibition. A reduction in theinterference effect reflects either a reduction in the incon-gruent RTs or an elevation of the congruent RTs or both.Assuming that the "neutral" RT is more or less constant, areduction in the incongruent RTs implies weakening of theinhibition component. In parallel, elevation of the congruentRTs implies reduction in the facilitation component. Webelieve that control reflects adaptive mental operations thatevolved in order to deal with specific situational demands (seealso Rozin, 1976). It follows that only the weakening of theinhibition (or the strengthening of the facilitation component)are consistent with the idea of control. Keeping this analysisin mind, we again examined the data. As can be seen in Table3, when subjects whose first language was Arabic were ex-pecting an Arabic written word and such a stimulus appeared,it reduced the RTs in the incongruent condition, F\l, 15) =10.66, p < .01, without affecting the congruent trials (F < 1).In contrast, expectation for Hebrew words affected congruentand incongruent Hebrew written stimuli to an equal amount,(F < 1, for the relevant interaction). Thus, it seems fair toconclude that expectations affect mainly the inhibition com-

Note. I.E. is the interference effect defined as the difference betweenreaction times in the incongruent and congruent conditions; Cong. =Congruent; Incong. = Incongruent.

3 During the last year we ran several (monolingual) Stroop experi-ments in which we manipulated the proportion of neutral trials. Aconsistent finding emerged from these experiments: the size of theStroop effect (and, to be more accurate, the inhibition component) ispositively correlated with the proportion of the neutrals. In otherwords, increasing the proportion of neutrals decreases control. Thus,according to our best knowledge the presence of neutral trials affectsthe very process of control: it decreases controllability.

BILINGUAL STROOP CONTROL 765

Table 3Mean Reaction Times in Experiment 1 (in Milliseconds) asa Function of Stimulus Language, Language Frequency, andColor Name Congruency

FrequentlanguageHebrewArabic

Cong.717762

StimulusHebrew

Incong.826884

I.E.109122

language

Cong.742738

ArabicIncong.

863814

I.E.12176

Note. I.E. is the interference effect defined as the difference betweenreaction times in the incongruent and congruent conditions; Cong. =Congruent; Incong. = Incongruent.

ponent of the Stroop effect, which is consistent with the ideaof control. This finding is not necessarily consistent withLogan's (1980) model of Stroop control that implies symmet-ric effects of control on facilitation and inhibition. Thus itmay be that several mechanisms of control exist. However,additional data are needed before reaching such a conclusion.

We would like to briefly mention two points. One is relatedto the relationship between expectations and the between-versus within-language pattern of interference. Expectations(i.e., the frequent language variable) did not influence thewithin-language versus the between-language pattern ofStroop interference. To the degree that the relations betweena within-language and a between-language pattern of interfer-ence reflect the underlying structure of the bilingual lexicon,the present pattern of results suggests that the issue of controlversus automaticity is independent from that of the structureof the lexicon. It also implies independence of the input andthe output aspects of language processing (MacNamara &Kushnir, 1971). The second point is related to control andlanguage proficiency. Our subjects reported better proficiencyin Arabic than in Hebrew. They succeeded in reducing theinterference effect for Arabic expected words but not forHebrew expected words. This pattern of results supports theclaim that one by-product of proficiency is control. In theStroop paradigm, control allows the subject to reduce theinterference effect. Accordingly, one may predict a reversedpattern of interference for subjects who are more proficientin Hebrew than in Arabic. That is, for such subjects oneexpects to find a reduced Stroop interference for Hebrewexpected words and little or no effect of expectation on Arabicwords. Our next experiment addressed this issue. In it, weused subjects who were more proficient in Hebrew than inArabic.

Experiment 2

The purpose of Experiment 2 was to replicate the mainfindings of the previous experiment; namely, to show thatStroop interference can be diluted when subjects expect astimulus in their first language. We used the same set ofstimuli but with subjects whose first language was Hebrewand whose second language was Arabic. In Israel, Arabic isstudied in high school as an elective, so a certain percentage

of Israeli high school graduates study Arabic for about fouryears. Out of this population, we recruited a sample of stu-dents for the present experiment. These subjects were there-fore less proficient in Arabic (i.e., their second language) thanwere Experiment 1 subjects in Hebrew (i.e., their secondlanguage). We assumed that the two samples were equallyproficient in their respective first languages.

With respect to automaticity and control, we expected tofind evidence for control, which should be reflected in areduction in the amount of Stroop interference in the firstlanguage. We found such a pattern in Arabic in Experiment1 and expected to find a similar pattern for Hebrew inExperiment 2. With respect to the structure of the lexicon,reflected in the within-language and the between-languagespattern of interference, it was possible that Experiment 2subjects would deviate from the pattern obtained in Experi-ment 1. Because Experiment 2 subjects were less proficient intheir second language than Experiment 1 subjects were intheirs, the present within-language interference may not belarger than the between-languages interference. Instead, wepredicted that Hebrew written words would cause a relativelylarge interference effect both when Hebrew was the responselanguage (i.e., a within-language condition), and when Arabicwas the response language (i.e., a between-languages condi-tion).

Method

Subjects. Sixteen subjects participated in the experiment, eitherin partial fulfillment of course requirement or for payment. Allsubjects were of Jewish origin and studied Arabic as a second languagefor 4 years or more. All of them were using Arabic in the restrictedcontext of work or academic studies and Hebrew in their dailyinteractions. Three of the subjects were high school teachers of Arabic,but even they declared that their knowledge of Hebrew was muchbetter than their knowledge of Arabic.

Procedure. All other details of the method were exactly the sameas those of Experiment 1.

Results

For each subject in each condition, we calculated the me-dian RT of the correct responses. These medians were sub-jected to a four-way repeated measures analysis of variance.Means and standard deviations of the median reaction timesin the various conditions of Experiment 2 appear in Table 4.

Congruent ink colors were named faster than incongruentstimuli, F(\, 15) = 79.56, p < .005. This interference effectwas moderated by the same two triple interactions that weresignificant in Experiment 1. The interference effect dependedon the correspondence between the stimulus and the responselanguage, resulting in a significant triple interaction amongstimulus language, response language, and congruency, F(\,15) = 12.42, p < .01. This interaction appears in Table 5.

It seems that there was no clear difference between thewithin- and the between-language conditions. The interfer-ence effects in three of the four combinations of stimulus-language and response-language were very similar. There was

766 J. TZELGOV, A. HENIK, AND D. LEISTER

Table 4Means (in Milliseconds) and Standard Deviations in the Experimental Conditions ofExperiment 2

Frequent language: Hebrew Frequent language: ArabicStimuluslanguage:Hebrew

Stimuluslanguage:

Arabic

Stimuluslanguage:Hebrew

Stimuluslanguage:

Arabic

Statistic

MSD

MSD

C

66297

721106

I

77494

811150

C I C I

Response language: Hebrew73192

746 674102 109

807125

Response language: Arabic708134

816 758161 136

899172

C

69374

69195

I

71381

781138

Note. C and I represent congruent and incongruent conditions, respectively.

one combination that was at odds with the other three. Theeffect shrank markedly when the words were written in Arabicand the subjects responded in Hebrew. The simple interactionbetween congruency and stimulus language was not signifi-cant when the subjects responded in Arabic, F( 1, 15) < 1, butit was significant when they responded in Hebrew, F(\, 15) =33.58, p < .001. Under the latter conditions there was a clear121-ms effect when the stimuli were written in Hebrew. Inaddition, there was a small and insignificant effect, in thesame direction, when the stimuli were written in Arabic, F(l,15) = 3.65,/;< .10.

The congruency effect was also dependent on the corre-spondence between the stimulus language and the frequentlanguage. This was indicated by the significant triple interac-tion among these variables, 7-1(1, 15) = 4.84, p < .05. Therelevant means appear in Table 6. This interaction resemblesthe one reported in Experiment 1. For the Hebrew writtenstimuli there was a significant congruency by frequent lan-guage interaction, F(l, 15) = 4.60, p < .05. The congruencyeffect was reduced when Hebrew was the frequent language(100 ms) relative to conditions in which Hebrew was infre-quent (136 ms). For the Arabic written stimuli there was nosignificant congruency by frequent language interaction, F <1. The congruency effect, across the two frequent language

Table 5Mean Reaction Times in Experiment 2 (in Milliseconds) asa Function of Stimulus Language, Response Language, andColor Name Congruency

ResponselanguageHebrewArabic

Cong.669740

Stimulus languageHebrew

Incong. I.E.790 121855 115

Cong.713700

ArabicIncong.

730799

I.E.1799

Note. I.E. is the interference effect defined as the difference betweenreaction times in the incongruent and congruent conditions; Cong. =Congruent; Incong. = Incongruent.

conditions, was clear, F(l, 15) = 39.19, p < .001. In contrast,the frequency effect for such stimuli did not reach significance,F(l, 15) = 3.28,p>.05.

Given the distinction between the effects on facilitation andinhibition components of the Stroop effect, we examinedanother partition of this interaction. Expectations for Hebrewwords resulted in significantly shorter RTs in the incongruentcondition, F(l, 15) = 6.32, p < .05, but not in the congruentcondition, F(l, 15) = 1.50, ns.

Stimulus language interacted with response language, F\l,15) = 6.30, p < .05, with frequent language, F( 1, 15) = 51.84,p < .001, and with congruency, F(l, 15) = 19.48, p < .001.In addition, response language interacted with congruency,F( 1,15) = 9.46, p < .01. These effects, however, were includedin the two triple interactions discussed above and thereforewere not analyzed any further.

Two additional main effects were significant. Responses inHebrew were faster than responses in Arabic, F\l, 15) = 6.27,p < .025, and Hebrew written stimuli resulted in longer RTsthan Arabic written stimuli, F(\, 15) = 13.64, p < .01.

Discussion

The subjects of the present experiment were less proficientin Arabic than in Hebrew. In general, their responses inHebrew were faster than their responses in Arabic. Further-more, when they responded in Hebrew there was only a verysmall interference by Arabic written stimuli.

The within-language interference effect was not necessarilystronger than the between-languages interference effect. Thewithin-language interference effect was 121 ms for Hebrewand 99 ms for Arabic stimuli. The between-language interfer-ence effect of Hebrew written stimuli was 115 ms, whereas itwas 17 ms for Arabic written stimuli. Hence the within-language and the between-languages Stroop effects revealedHebrew dominance (which was in agreement with the fasterresponses in Hebrew). This pattern of results does not fit theconcept mediation hypothesis, which was in agreement withExperiment 1 results. In fact, at least the relative sizes of these

BILINGUAL STROOP CONTROL 767

Table 6Mean Reaction Times in Experiment 2 (in Milliseconds) asa Function of Stimulus Language, Language Frequency, andColor Name Congruency

FrequentlanguageHebrewArabic

Cong.692717

Stimulus language

Hebrew

Incong. I.E.792 100853 136

Cong.720692

Arabic

Incong.781748

I.E.6156

Note. I.E. is the interference effect defined as the difference betweenreaction times in the incongruent and congruent conditions; Cong. =Congruent; Incong. = Incongruent.

interference effects are in agreement with the word associationhypothesis. A similar pattern of results was reported by Chenand Ho (1986) for Chinese speakers who were at the firststages of learning English. It also fits the proficiency hypoth-esis suggested by Magiste (1984).

As in the previous experiment, we found evidence forcontrol. The pattern here was similar to the results found inExperiment 1. In Experiment 2, as in the previous experiment,only the RTs in the incongruent conditions were affected byexpectations for stimuli written in Hebrew. We found similarStroop effects for stimuli written in Arabic regardless of theirexpectancy level. Even though on certain sessions the subjectsknew that the next stimulus would probably be written inArabic, they could not suppress reading the irrelevant colorname. In contrast, expectation influenced the size of theinterference of color names written in Hebrew.

It should be noted that expectations did not influence therelations between the within-language and the between-lan-guage pattern of Stroop interference. The same was true inExperiment 1.

General Discussion

We used the same set of stimuli in two experiments withArabic-Hebrew bilinguals. The subjects in the two experi-ments differed in what they defined as their first language andin their proficiency in their first and second languages. Thesubjects who took part in Experiment 1 were quite proficientin the two languages and their first language was Arabic. Thefirst language of the subjects who took part in Experiment 2was Hebrew; however, these subjects were much more profi-cient in their first language (Hebrew) than in their secondlanguage. Certain differences in the results of the two experi-ments stem from these differences. The results of the twoexperiments have significant implications for the two issuesaddressed earlier, namely, the structure of the bilingual lexi-con and the issue of automatic versus controlled characteris-tics of skilled performance.

In the first experiment the within-language Stroop effectwas larger than the between-language effect. The pattern ofthe between- and the within-languages interference effects didnot reveal dominance of either Arabic or Hebrew. In contrast,the interference created by Hebrew in the second experiment

was relatively large in both the within-language and the be-tween-language's conditions, whereas the interference createdby Arabic was relatively large only under the within-languagecondition. Thus, in the second experiment, Hebrew emergedas the dominant language. The pattern of results in the firstexperiment is in agreement with the concept mediation hy-pothesis, whereas that of the second experiment is in agree-ment with the word association hypothesis. Taken together,the results of the present experiments fit the mixed model ofconcept representation advocated by Chen and Ho (1986).They suggested that at the first stage of learning a secondlanguage, subjects access the new language via the represen-tations of the first language (i.e., the word associations hy-pothesis). As proficiency in the second language increases,dependence on the first language decreases and subjects tendto rely on amodal concepts. Chen and Ho (1986) and Chenand Leung (1989) reported such a pattern of results withChinese-English bilinguals. However, Potter et al. (1984) didnot find indications for such a mixed model of conceptrepresentation. Hence, it is possible that such a model islimited to very concrete concepts such as colors.

The fact that the pattern of results in Experiment 1 isconsistent with the concept mediation hypothesis, whereasthe results of Experiment 2 are consistent with the wordassociation hypothesis, may also be interpreted in a differentway.4 The subjects in Experiment 1 learned their secondlanguage in early childhood, whereas the subjects in Experi-ment 2 acquired their second language as adolescents. Re-cently, Johnson and Newport (1989) extended the concept ofa critical period of language acquisition to second languageacquisition. Thus the differences found between the groupsmay reflect the fact that the subjects in Experiment 1 acquiredtheir second language during the critical period, whereassubjects of Experiment 1 acquired their second language afterthe end of the critical period.

What about the proficiency hypothesis suggested by Magiste(1984)? According to this hypothesis, the degree of interfer-ence created by a language is directly related to the proficiencyin that language. Note that this monotonic relationship be-tween proficiency and the Stroop effect is not limited tolearning a second language. It can be found when childrenpractice their first language (e.g., Schiller, 1966). However,this pattern of results, which fits the word association hypoth-esis, is limited to the initial stages of learning a language (beit the first or the second language). At these initial stages oflearning, interference reflects the progress towards automati-zation of the reading process. The proficiency hypothesis doesnot capture the phenomenon of control that apparently char-acterizes the more advanced stages of language learning. Inother words, further practice does not necessarily increaseinterference; it may even reduce it. A pattern of resultsconsistent with this interpretation was reported by Ehri andRyan (1980). They investigated interference of words in apicture-naming task. They found that words written in the

4 This interpretation was implied in a comment by one of theanonymous reviewers of an earlier version of this article.

768 J. TZELGOV, A. HENIK, AND D. LEISTER

second language of their bilingual subjects produced moreinterference than words written in their first language. Inaddition, Fang et al. (1981) found larger Stroop interferencein the second language of their Chinese-English and Spanish-English bilinguals.

Fang et al. (1981) have shown that the magnitude of reduc-tion from within- to between-language Stroop interference isa linearly decreasing function of orthographic similarity. Ar-abic and Hebrew differ in their orthography. Accordingly,taking Fang et al.'s (1981) analysis as a starting point, oneshould expect a reduction of at least 110 ms (see Fang et al.,1981, Table 3, p. 613) in the between-language's (Arabic-Hebrew or Hebrew-Arabic) in comparison to a within-lan-guage condition. Such a reduction would be comparable tothe reduction in a switch from a within- to a between-languages condition in Hungarian-English and Japanese(Kana)-English bilinguals. In contrast, the reduction of theinterference effect in the between-languages condition of ourArabic-Hebrew bilinguals was considerably smaller (see Ex-periment 1, Table 2). In Experiment 2 the interference effectin the Hebrew-Arabic condition was larger than the interfer-ence in the Arabic-Arabic condition (see Table 4). We arenot claiming that orthographic similarity is not important. Itseems, however, that the relative language proficiency, asreflected in the mixed model presented earlier, is the domi-nant factor in determining the pattern of bilingual Stroopeffect.

Can the sensitivity of the interference to language frequencybe explained as resulting from increased practice? Dyer (1971)compared the interference to color naming of (incongruent)color words written in seven different languages in a bilingualStroop task. He found that the conditions that produced thegreatest interference in color naming showed the greatestimprovement over sessions. In parallel, it may be suggestedthat the smaller interference in the 80% condition reflects thefact that the subjects had more opportunity to practice withstimuli in a frequent language and that this effect of practicewas stronger for the language that interferes more. To rejectthis possibility, we reanalyzed our data in search of possiblepractice effects. As described in the method section of Exper-iment 1, there were four groups of subjects that differed inthe order of sessions. Because the sensitivity of the Stroopeffect to frequency was limited to the first language of oursubjects, we focus first on that language. The practice hypoth-esis predicts that sensitivity of the Stroop effect to languagefrequency should be greater in the groups in which the (first)language was frequent in the first two sessions than in thegroups that were run in an opposite order of sessions. Thisprediction is based on the idea that the effect of practice isdominant mainly during the first two sessions. Furthermore,at the end of the fourth session the amount of practice wasequal in all four groups. Therefore, the practice effect shouldact to amplify the influence of the frequency variable whenthe frequent conditions preceded the infrequent conditions.It should also act to reduce the influence of the frequencyvariable when the infrequent conditions came before thefrequent conditions. This in turn implies an interaction be-tween the "group" variable and the remaining variables (ex-

cluding response language) of the experiments. However, inboth experiments, none of the interactions including simul-taneously group and language frequency approach signifi-cance. Assuming a significance level of .05, the critical F ratiofor each of these interactions is 3.49, whereas the highest Fratio obtained in the case of the above mentioned interactionswas 2.33. Thus an "increased practice" explanation of ourresults can be rejected.

It may be assumed that an increase in language proficiency,and in reading in particular, affects mainly reading time andnot color-naming time. It usually takes less time to read acolor word than to name its color (Dyer, 1971). Increasedlanguage proficiency should result in an easier discriminationof the arrival times of color names and word names. Thus, ifthe (irrelevant) color word consistently proceeds the (relevant)color name, these arrival time relations could be used as acue for selecting the relevant (or suppressing the irrelevant)information. It would also leave more time for disregardingthe irrelevant information. Such a model predicts a decreasein the interference with increased proficiency. However, it ishard to see how it could explain the sensitivity of the interfer-ence to frequency unless one claims that our frequency ma-nipulation reflects additional practice that leads to additionalproficiency. We have already shown that an "increased prac-tice" interpretation of the frequency effect is unlikely. Inaddition, it seems unrealistic to assume that this relativelyshort "practice," in which reading is in fact undesirable, hasa significant effect on reading proficiency.

Expectations may affect processing time of stimuli in thesecond language as well. In Experiment 1 the processing ofHebrew written stimuli was accelerated by expectations thatmost stimuli in a block were going to be in that language. Itshould be stressed that in this case it is not the Stroopinterference that is influenced. When Hebrew words are ex-pected they are processed faster than when they are unex-pected. Note that this happens even though the meaning ofthe word is irrelevant and that the effect is independent ofcongruence. The Stroop effect reflects differences in the (color)word meaning, and as such it reveals processes in the semanticnetwork. In contrast, expectations for the less known languagedo not affect the semantic level of processing, but they stillmay enhance the general level of performance by speeding upthe access to the lexicon of the expected (but to be ignored)language. We believe that this general effect on reaction timesreflects increased automaticity rather than control. It seemsthat in the process of increasing language proficiency, humansacquire the ability to focus on that language. This selectivityof processing because of increased proficiency is similar tothe idea of "tuning" as used by Anderson (1982). In Experi-ment 2, expectations for stimuli in the second language (Ar-abic in this case) did not reduce reaction times. This patternof results is consistent with a mixed model of representation.The subjects in the second experiment were at the first stagesof learning Arabic and, according to the mixed model, theiraccess to the semantic level was always mediated by Hebrew.Therefore they did not benefit from expectations for Arabic;their access to the semantic network was through the Hebrewlexicon in any case.

BILINGUAL STROOP CONTROL 769

Logan (1985) pointed out that skilled performers wereusually able to control their performance better than unskilledperformers, in spite of the fact that skilled performance wascharacterized by automaticity. Thus, control increases ratherthan decreases with skill. Similarly, our results indicate thatStroop interference is controllable, and that proficiency is aprecondition for such control. In both experiments we foundthat subjects were able to decrease the interference of theexpected language. Hebrew-speaking Arabs, in Experiment 1,were able to do it only for the Arabic stimuli, whereas theArabic-speaking Jews, in Experiment 2, were able to do itonly for the Hebrew stimuli. Note that control was limited;the Stroop effect did not disappear, it shrank. This fact wasquite prominent in Experiment 2; interference of Hebrewstimuli was smaller in the 80% Hebrew stimuli condition thanin the 20% Hebrew stimuli condition. Nevertheless, the inter-ference created by Hebrew words was still larger than theinterference created by Arabic words. The results of the twoexperiments indicate that language proficiency was a precon-dition for control.

This implies a curvilinear relationship between Stroop in-terference and reading proficiency in a given language. Aminimal level of reading proficiency is required to obtain theinterference at all. One has to know that the letters R-E-Dmean "red" for their appearance to interfere with perform-ance. Automatization of the reading tasks that follow practicespeeds up the reading process, and as a result interferenceincreases. In the advanced stages of acquiring the proficiencyin reading, one learns to apply control mechanisms to thereading processes, and as a result interference diminishes.According to this analysis, one should expect interference toincrease at the first stages of learning a language and todecrease later on. This pattern was indeed found by Schiller(1966).

We would like to suggest that the present (and similar)evidence for controlled processing reflects the operation ofconsciousness. Several authors have emphasized the role ofconsciousness in the development of new behaviors (Carr,1979; Rozin, 1976). This idea is in accord with conceptuali-zations of consciousness as a mechanism that controls andselects specific subroutines during performance of varioustasks (Frith, 1981; Keele, 1973; Shallice, 1972). The presentresults do show that control, reflected in the ability to withholdcertain automatic processes, may be evidenced in skilledreaders. Furthermore, it seems that such control emerges onlywhen the readers are really proficient in a given language.Note, however, that the present results evidence automaticity(i.e., Stroop interference) and control (i.e., a reduction ofStroop interference under certain conditions) simultaneously.We would like to agrue that automaticity and control are bothcharacteristics of skilled performance, but each reflects adifferent aspect of the system, and each subserves, essentially,a different function. The present pattern of results supportsthe notion that automatic and controlled processing may exerttheir influences simultaneously.

Our last comment is concerned with two related issues, thelocus of the Stroop effect and the source of the control process.One group of models attributes the effect to the perceptual

encoding stage (e.g., Hock & Egeth, 1970). Such modelsassume that the interference effect discloses a breakdown ofselective attention. The perceptual encoding models havebeen criticized because they cannot explain why congruentstimuli, which have the maximal semantic similarity betweenthe word and its color, do not cause maximal interference(Seymour, 1977). Another group of models (e.g., Morton,1969; Posner, 1978; Stroop, 1935) explains the interferenceas resulting from response competition between the processof color naming and the relatively faster process of wordreading. Such "horse race" explanations of the Stroop effectthat predict a monotonic relationship between proficiencyand interference have been recently evaluated and criticizedby Dunbar and MacLeod (1984). Our results, which point tothe decline in interference in the better known language,constitute a further challenge to the simple horse race modelinterpretation of the Stroop phenomenon. In addition, theability to control the interference was independent of theresponse language. In other words, the ability to reduce theinterference was not affected by the proficiency of languageof response. This is another indication against a responsecompetition explanation of the Stroop effect.

It seems that our results are best explained in terms ofSeymour's (1977) "conceptual encoding" model. The modelplaces the locus of interference at the semantic level andattributes it to the simultaneous activation of two nodes inthe semantic network. The extra processing time reflects theprocesses involved in the suppression of the irrelevant acti-vation. Such an interpretation is consistent with Neill's (1977;Neill & Westberry, 1987) and Tipper's (1985) proposal thatselection of relevant information may proceed by inhibitionof irrelevant information. Tipper and his coworkers (Tipper,1985; Tipper & Cranston, 1985; Tipper & Driver, 1988;Driver & Tipper, 1989) have shown that unaffected stimulihave negative priming effects. This implies that the unat-tended primes were identified before being inhibited. It maybe that a similar process is reflected in the Stroop effect. Ifthat is the case, our results imply that language proficiencyand expectations determine the efficiency of the suppressionprocess.

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Tzelgov, J., & Henik, A. (1989). The insensitivity of the semantic Revision received November 20, 1989relatedness effect to surface differences and its implications. Paper Accepted December 29, 1989 •