C81MPR Practical Methods (Lab 1)

Dr. Danielle Ropar & Dr. Jonathan Stirk

Stroop (1935)

Stroop (1935) Exp’t 1: had subjects read out loud the names of colour words printed on cards in different coloured inks.

Each card had 100 colour-names on it. Words in the experimental list were all incongruent

(e.g., RED written in YELLOW: RED) The control-condition cards were identical but all

the colour-names were written in BLACK ink. The results showed no differences in time taken to

read the word lists for the control and experimental groups

So: when word name and word colour are incongruent, naming the word is not interfered with

However!

Stroop (1935) Exp’t 2: had subjects read out loud the colour of the words printed on cards

For the control condition he used coloured squares in the list

This time the experimental group took longer than the controls

So: When the colour of the ink and the word name are incongruent (don’t match), the word name interferes with naming the ink colour.

Stroop variant

In a variation of Stroop’s experiment, we can present subjects with colour names in either the matching (congruent) or non-matching (incongruent) ink.

Congruent (e.g., RED written in RED: RED) or Incongruent (RED)

When subjects name the colour of the words they are slower on incongruent trials than on congruent ones

This is known as the STROOP EFFECT

Beware the Stroop!

It’s everywhere!

Try it yourself!

Try naming the colour of the ink for the words below as quickly as you can:

RED

BLUE

GREEN

YELLOW

CONGRUENT CONDITION

RED

BLUE

GREEN

YELLOW

And again…

Try naming the colour of the ink for the words below as quickly as you can:

INCONGRUENT CONDITION

Independent & dependent variables This design uses the experimental method

(see stats lecture 2). In this experiment we have 1 IV which we are manipulating at 2 levels– Congruency

Congruent vs. Incongruent Our DV is what we actually measure and is

normally the time taken to read lists or reaction time to make a response (in the exp’t you are about to do)– Time is normally measured in seconds or

milliseconds (thousandths of a second). We will use milliseconds (msecs) in today's experiment.

– This DV uses a RATIO scale of measurement.

Explaining the Stroop effect There are a number of theories used

to explain the Stroop phenomena Two are:

–Relative Speed of Processing –Parallel Processing

There are others which we will not discuss today

Relative speed of processing In the incongruent condition, the two dimensions of

the stimulus (colour and word) are involved in a 'horse race' competing to see which can get to elicit the response (response competition)– The word name response often wins the race because it is

assumed that reading a word is faster than naming a colour

Then there is a competition for control of the response – This takes time which accounts for the Stroop Effect

Button PressInk ident.Slow

Word ident.

Decision

Fast

Speed of processing

Both attributes arrive at different times to a decision making component which has limited capacity and can only process one input at a time (serially)

PROBLEM: This theory cannot account for the Reverse Stroop effect (reversal of interference: colour of word ink interfering with word naming) –see next slide

Speed of processing account doesn’t predict reverse interference

Button PressInk ident (BLUE) Slow

Word ident (RED)

Decision

Fast

So, in the reverse task you have to name the WORD

In the incongruent pairing: RED

Button PressInk ident (RED) Slow

Word ident (RED)

Decision

Fast

In the congruent pairing: RED

Parallel processing

The general idea is that potentially relevant evidence is collected until a decision is reached about which response to make. – When there is a conflict between different sources of

evidence it takes longer to reach a decision. The Parallel processing utilises the strength of the

pathways that convey information that is important rather than the speed of processing. – Pathways that have become automatic have greater

strength and this leads to the asymmetry that produces the Stroop effect.

This model appears to be able to handle all the empirical findings related to the Stroop effect.

Parallel processing

Button Press

Ink ident.

Word ident.

Decision“accumulator”

Information arrives simultaneously

Stronger pathway

Weaker pathway

Separating the theories If we reverse the task (recognise word and ‘ignore’ ink

colour) what do the two theories predict?

Speed account: There will be no reverse Stroop effect because word form would have been processed and decision made before ink was recognised

Parallel systems: There will be a significant, but weaker, effect because the two signals are being processed (even though the ink signal is weaker). So we might expect to find some reverse interference

A journal article

HALF A CENTURY OF RESEARCH ON THE STROOP EFFECT - AN INTEGRATIVE REVIEW

MACLEOD CMPSYCHOLOGICAL BULLETIN 109: (2) 163-203 MAR 1991  

Abstract:

The literature on interference in the Stroop Color-Word Task, covering over 50 years and some 400 studies, is organized and reviewed. In so doing, a set of 18 reliable empirical findings is isolated that must be captured by any successful theory of the Stroop effect. Existing theoretical positions are summarized and evaluated in view of this critical evidence and the 2 major candidate theories-relative speed of processing and automaticity of reading-are found to be wanting. It is concluded that recent theories placing the explanatory weight on parallel processing of the irrelevant and the relevant dimensions are likely to be more successful than are earlier theories attempting to locate a single bottleneck in attention.

Conducting a literature search

Basic steps

Define the enquiry Gather Background Information Carry out the Search Locate the References Compile a reference list of cited

material

Define the enquiry

There are two basic questions that need to be answered– What kind of information is needed?– How much detail is required?

Gather background information Read textbooks relevant to the

area Use subject dictionaries and

encyclopaedias Look up any reference material

that you have already been given Generate a list of keywords with

which to search databases– E.g. Stroop task

Carry out the search & locate references There are both printed and

electronic databases of references

Printed databases, e.g.– Psychological Abstracts

Electronic resources, e.g.– PsycINFO, ISI Web of Science (WOS)

Both require you to log on to your University account

– University of Nottingham Library

Compile a reference list Remember two points when

referencing published material– Give sufficient detail to enable anyone to

identify the book or article to which you are referring

– Give the references in a consistent form Normally the APA format (see APA citation guide

at Ohio State University) Use secondary citations for work that you

haven’t read directly