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Improvement and further weaknesses found in the Stroop Effect Experiment.

Submitted: December 07, 2016

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Submitted: December 07, 2016







The aim of the current investigation was to examine the Stroop effect and reinforce the theory that demonstrates an interference in reading ink colour of word lists. First-year psychology undergraduates were shown three lists of words (nouns, nonsense and colour) and time taken to read ink colour was recorded. It was predicted that participants would have found a slowdown in naming colour words. Subsequently, results demonstrated that colour ink naming was obstructed when the task was to name colour words. In short, when the word “green” was written in “blue” ink, participants were much slower in naming the ink colour than when the ink did not spell a colour name or spelt the coinciding colour name. It was concluded that the denomination of the colour was slower than the reading of the word, the denomination of the colour was influenced by the semantic information of the word itself and the ink colour did not influence the reading of the word. Therefore, the denomination of the colour must be a controlled process.




Before introducing the several research on Stroop effect, it is essential to examine briefly the functions of the brain related to the Stroop interference, their biological processes and the difference between automatic and controlled processing since they allow us to understand the two tasks that participants' minds are called to perform during the experiment. Schneider and Shiffrin (1997) argue that most cognitive elaborations can be characterised in terms of processes which require a conscious control, or of processes that instead do not require this kind of control». All the activities that are carried out by the  individual in a rapid and precise way and without the necessity of a conscious programming or control during the course of their achievement are defined as automatic processes. An automatic process requires a generic and attentive alert, with a minimum use of resources, since it is predisposed to sustain durable tasks and activities that are able to be maintained for a long time. Language activities, spontaneous motor activity, but also reading and writing are possible precisely because the processes that are involved with them were automated. Controlled processes are based on conscious control; these processes are serial in nature and require a relatively long time for their implementation. So this kind of processes requires an attention that is not generic, but it is focal, since it is directed voluntarily and its intensity can be adjusted intentionally, but it causes a high expenditure of resources so that it can be used only for short periods. (Sternberg, 2000). Moreover, most automatic processes regulate relatively easy tasks and controlled elaboration manages most difficult tasks. However with sufficient practice, even highly complex tasks, such as reading, may become automated. Since highly automated behaviours require very limited effort or conscious control, we can often be engaged in more automatic behaviours at once, but we can rarely be active in more than one controlled behaviour that requires a commitment of a particular intensity. (ibidem). To conclude, the attentional capacity for humans is key for action and it influences the participants' performance of the current experiment.  An attentional function approach, which attempts to consider the need to choose an appropriate behaviour for different situations, is called “action selection." (Allport,1987). Some aspects of this theoretical approach are shared and supported in "Gibson's theory of perception" (1979). This attentional behaviour-based approach has been successfully applied to explain the changes in the nature of attentional processing that is detectable during the carrying out of experiment tasks, where different types of responses are required. (Brown, 1996) (Allport, 1993).


The Stroop Test (CWT) dates back to experiments conducted by Cattell, about

tracking differences between colour naming and word creating, (1886) and research

by Jaensch, on situations of interference created by the colour designation of the ink

with which the name of a different colour is written (1929). Incongruous colour

interference in reading the word, which concerns one of the trials in the test, was

later indicated as ' reversed Stroop interference ' or ' Stroop effect '. Stroop test

results were usually explained and interpreted in terms of automatic-controlled

processing: for example, this distinction was briskly supported in the research of

Posner and Snyder (1975). The authors consider the reading of the word as an

automatic, involuntary and cognitively undemanding process.  The denomination of

the colour is a controlled process and requires effort and attentional supervision.

Automatic processes do not require attention for their implementation, and

Stroop test seems to suggest that the reading of the world occurs even when the

attention is used to ignore or suppress the information of the word. Recent research

has underlined that the automatic effects of word reading, found during the Stroop

task, are influenced by the context of the task, (Berkovits & Algom 2000), by the

attentional regulation, (Besner, Slotz, and Boutilier, 1997), and by the reciprocal

compatibility between stimuli and by the type of answer required. (Durgin and Zhang

and Kornblum 1998). These findings support the hypothesis that interprets the

automaticity as a relative phenomenon, rather than absolute one, characterized by

the codification of a particular representation of stimulus-response that directly

involves the attention and the context. Furthermore, numerous studies have shown

that the practice gradually produces and continuously increases the processing

speed. MacLeod and Dunbar (1988) examined this variable by subjecting

participants to a learning task of form naming, with 144 tries in 20 days.  The

response times showed a gradual and steady improvement with practice. The

effects of the observed interference patterns by the authors suggest that the

processing speed and interference effects assume a continuous nature and are

strictly dependent on the practice. In addition, the data indicate that both the

processing speed and the effects of interference can be used to identify whether a

process is automatic or controlled. One of the explanations of the reasons why the

Stroop test is so challenging could be that the majority of people read as an

automatic process, outside conscious control. Therefore, it is difficult to overlook

intentionally the colour name of the written word and to focus solely on ink colour

designation. MacLeod (1991), proposed an alternative explanation, arguing that the

output of a response takes place when the pathways of mental processing are

sufficiently activated to produce an answer. In the test, the coloured word would

activate a cortical information flow to read out that word, while the name that

matches the colour of the ink would activate another flux for the colour naming; these

two simultaneous activation pathways interfere with each other. In this situation, it

takes longer to reach the sufficient activation force to provide the name of the colour

rather than to the answer of word reading since the first one is in conflict with the

latter. (Sternberg, 2000).


An additional feature of the Stroop effect under analysis was the elaboration speed

of the word, which results in a more rapid and superior information elaboration

process of the colour, justifying the absence of interference effect of colour in the

reading of the word. This feature of processing speed has been studied by Glaser

and Glaser (1982), varying both colour information and speech, using the

experimental paradigm of Stimuli Onset Asynchrony, (SOA). Therefore, the authors,

considering the original data of processing speed detected during the Stroop test,

designed an experimental situation where it was possible to submit colour first

and then the word, to test the hypothesis of the interference presence of the colour

on the word. Results showed that the colour, which was presented 400 ms before

the word, had theoretically no effect on the reading of the word. Therefore, these

findings support the hypothesis that the neural circuit of reading the word is stronger

than the neural circuit of the colour name.


During the current experiment, participants will be tested to elaborate controlled

process and ignore automatic ones through a Stroop interference. They will have

three different lists of words where they have to read out the colour of the ink

each word is written in, and they will find out that one list will be more difficult to read

rather than the others. The current aim of the study will be to reinforce the previous

findings of the Stroop effect and to understand the effect of the colour word list on

the time taken to name the ink of the colours themselves. The independent variable

for this experiment will be the type of world list, and it will based on three levels:

nouns, nonsense and colour words. On the other hand, the dependent variable will

be the time taken to name the ink of colours. The data type will be ratio and the

design will be within subjects, or repeated measure since every participant will be

involved in all the three conditions. To conclude, the two-tailed Hypothesis argues

that there will be an effect of the type of word list on the time taken to name ink






Ninety-six first year Abertay psychology students (73 females and 23 male)

participated in this experiment. They were recruited through a convenience sampling

during a psychology practical lesson. Every student had to take part in every

condition with a total of three conditions.


Materials and Apparatus

The materials used in this investigation were a pc for every participant and a collection sheet. This one was structured by three different vertical columns which represented nouns, nonsense and colour words. Each participants had the chance to attempt each column twice and then a mean was calculated between results of each attempt. (see appendix 1). Furthermore, there was an instruction sheet (see appendix 2), a stopwatch and three lists of twenty words each that represented three different conditions. The first world list was represented by simple nouns (design, alarm, and pencil), the second one had nonsense words (wourdle, lollipo, vintog) and the third one nouns of colours. The colours used for the three lists were red, green, orange, brown and yellow. The SPSS system was used to analyse data and find descriptive and inferential results.



The experimenter gave details regarding the procedures by instruction sheet. Participants were divided into couples: a person  was in front of the pc and had to read out the colour of every ink of the three different word lists as fast as he could while the other student had to time the process through a stopwatch until the end and report time on the table. Every table contained two trials and the means between them had to be calculated. Furthermore, students were asked to ignore mistakes during the reading and they had to go on until the last word. Once one student had finished, the couple swapped  their tasks. When they finished,  the experimenter collected all table results asking to specify the gender of every participant. All the data collected by the experimenter were represented on the SPSS system though a table where data for every condition were showed and which could be analysed by the system to find the mean and create a graph for the results.







Figure1. Shows the time taken to name ink colours for nouns, nonsense and colour

words. From figure 1 we can note the mean time taken to read nouns which is 13,35

seconds. In addition, the mean for the time taken to read nonsense words is 13,33

seconds. Lastly, the mean of time taken to read colour words is 18,15. Furthermore, the 95% confidence intervals for mean of nouns is 12,57 for lower bound and 14,13 for upper bound. The 95% confidence intervals for mean of nonsense words is 12,66 for lower bound and 13,99 for upper bound. To conclude, the 95% confidence intervals for mean of colour words is 17,19 for lower bound and 19,11 for upper bound. To examine  observed differences in time taken to name ink colours for nouns, nonsense, and colour conditions, three paired samples t-tests were carried out and the time taken to name ink colours for the coloured condition was significantly longer than the nouns condition [t (95) =14,358, p< .001] and the time taken to name ink colours for colours condition was significantly longer than nonsense condition [t (95) = 15,518, p< .001]. There were no other significant differences.





The hypothesis was that there would be an effect of type of word list on the time taken to name ink colours and it was supported since there was a marked effect of colours word list on the time taken to name them and a clear interference for the colour list while there was no interference for the other lists. In the graph, it is possible to point out an evident gap between the mean of the time taken to read both the nonsense words list and the nouns list in comparison with the mean of the time taken to read colours words list. Previous research directly applied to the Stroop task the distinction between automatic and controlled processes, considering the following three assumptions: the reading of the word is automatic, the name of the colour is controlled and if the outputs of one of two conflicting processes, one of the two processes will be slowed down. In the current experiment, it was possible to reveal that the reading of the word was faster than the denomination of the colour because, according to Glaser, the neural circuit for reading the word is faster than the neural circuit to name the colour. The actual result was that the ink colour with which a word was written had no effect on word processing, because the process of naming colour is controlled, and then voluntary. Therefore, the process of colour naming was not triggered when the task was to ignore colour and read the word. (Michael Posner and Charles Snyder). From the experiment, it has been found that a word in conflict with its own ink colour, interfered with the naming of the colour itself because the automaticity of reading the word interfered with the outputs, causing a slowdown in response. The interference between the colour name and the colour ink was especially represented by the continuous mistakes by participants to read out the colour words list. Moreover, according to MacLeod, reading has become a highly automated process, outside consciousness for most adults, and therefore for students as well. For this reason, it was difficult to intentionally prevent from reading and  focusing solely on ink colour designation, without paying attention to the colour name of the written word.

Otherwise, attention and inattention could have played a main role during the experiment as Gibson argues. This was due to the effects of external variables such as noise, tiredness or distraction that were able to influence the participants’ performance. Furthermore, the population of the experiment was not fully representative since the proportion between sexes was approximately 3:1 since a number of 73 females and 23 males participated. On the other hand, the experiment could be improved not only by dividing the participants with the same percentage of males and females but also selecting the first language of participants. Participants who have a different first language could have gathered different results from the mean and they could have represented bias for the mean itself. Foreign participants with a different first tongue from English could have a weaker interference in reading out the colour word list since they have a different “automatic threshold” in recognizing words that are not in their native language. For example, even if they can recognize their native word for the colour “black”, the colour ink reading will be less automatic than an English native speaker one and they will be able to read out every list with no interference or with a completely weaker and different one from the mean. To sum up, a suggestion for the experiment could be to exclude foreign participants with English mother tongue and participants with different first language from the British one since the language itself influences the controlled and automatic elaborations and therefore the performance of participants. In conclusion, it is stated that the denomination of the colour is slower than the reading of the word, the denomination of the colour is influenced by the semantic information of the word itself and the ink colour does not influence the word reading. Therefore, the denomination of the colour must be a controlled processing.




Allport, A. (1993) and Styles, E. A. (1997). The Psychology of Attention. Hove: Psychology Press Ltd.

Allport, A. (1987). Selection for Action: Some Behavioral and Neuropsychological Consideration of Attention and Action. In H. Heuer & A. F. Sanders (Eds.), Perspectives on Perception and Action. London: Lawrence Erlbaum Associates.

Besner, D., Slotz, J. A., & Boutilier (1997). The Stroop effect and the myth of automaticity. Psychonomic Bullettin & Review, 4(2), 221 – 225.

Brown T. L. (1996). Attentional selection and word processing in Stroop and word search task: The role of selection for action. American Journal of Psychology, 109(2), 265 – 286.

Cattell, J. M. (1886). The time it takes to see and name objects. Mind, 11, 63 – 65.

Dishon Berkovits, M, & Algom (2000). The Stroop effect: It is not the robust phenomenon that you have thought it to be. Memory and Cognition, 28 (8), 1437 – 1449.

Durgin, F. H. (2000). The reverse Stroop effect. Psychonomic Bullettin & Review, 7(1), 121 – 125.

Gibson J. J. (1979). The ecological approach to visual perception. Boston: Houghton Mifflin.

Glaser, M. and Glaser, W. (1982). Time course analysis of the Stroop phenomenon. Journal of Experimental Psychology: Human Perception and Performance, 8(6), pp.875-894.

Jaensch, E. R. (1929). Grundformen menschlichen Seins. Berlin: Otto Elsner.

MacLeod, C. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bullettin, 109(2), 163 – 203.

MacLeod, C. M., & Dunbar, K. (1988). Training and Stroop – like interference: Evidence for a continuum of automaticity. Journal of Experimental Psychology: Learning, Memory, and Cognition, 14, 126 – 135.

Posner, M. L., & Snyder, C. R. (1975). Attention and cognitive control. In R. L. Solso (Eds.), Information processing and cognition (pp. 55 – 85). Hilsdale, NJ: Erlbaum.

Robert J. Sternberg. (2000). Attenzione selettiva. cit., p. 101.

Schneider, W., & Shiffrin, R. (1977). Controlled and automatic human information processing. Psychological Review, 84, pp. 1 – 66

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Zhang, H. Z., & Kornblum, S. (1998). The effects of stimulus – response mapping and irrelevant stimulus – response and stimulus – stimulus overlap in four – choice stroop tasks with single – carrier stimuli. Journal of Experimental Psychology – Human Perception and Performance, 24(1), 3 – 19.




Appendix 1:  Instructions for Participants


You will be presented with a list of words. Going from the top of the list and reading

down, read out the COLOUR of the ink each word is written in. Try to do this as quickly

and accurately as possible but don’t worry if you make a mistake, just ignore it and

keep going. As soon as you begin reading out the words, the experimenter will start

the stopwatch. When you have read out the colour of ink that the last word is written in, say “stop” and the experimenter will stop the stopwatch.


The data collection sheet consists in a table that shows two trials and the mean of the participants’ time taken to read every word list.

Appendix 2:  Data Collection Sheet




 (List 1)


(List 2)

Colour Words

(List 3)

Trial 1




Trial 2








© Copyright 2020 Francesco Galdiero. All rights reserved.

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