(Editor:   Sue Frantz)


The Stroop effect is a classic cognitive psychology experiment discovered and first studies by J. Ridley Stroop (Stroop 1935/1992). In this classic study, if the person is trying to name the color that a word is printed it, it take longer if the word is also a color word, but a different color. So it is takes more time to name the color green if the word printed in green is "red". The most common explanation for this effect deals with what is called response competition (Lien& Proctor, 2002). The response to both the color and the word are formed but we can only make one response at a time. The response to the word is a little faster than the response to the color so it interferes with our attempt to name the color. The fact that we respond faster to the word is often taken as an example of automaticity where some responses are processed automatically with out our conscious processing (Marmurek, 2003).


In this experiment, a word is presented in the middle of the screen. Usually it is a color word such as "green" and it will be written in some color, say red. So the word might look like green. The participant usually is asked to name the color of the word. The response in this example would be red. After the participant responds, the next word is presented. The computer records the person's response to check accuracy and also the reaction time of the response.

The essence of an experiment is that the experimenter changes some value of some variable and sees what happens. In this version of the Stroop experiment, you have that chance. There is a basic setup that you can use but you can also change some of the conditions of the experiment to study some more complicated questions. First the basic design will be discussed and then each of the variables that can be manipulated to extend the experiment.

Basic Design

In the basic experiment, there are 20 words both where the color word and the color of the word match (congruent) and 20 words where the color word and color of the word do not match (incongruent). The order of the two conditions are randomly selected by the computer and the condition is identified before the experiment begins.


These variables are listed on the instruction page but will be summarized here.

  • Number of conditions to test. You can test as few as one condition at a time or as many as four at a time. By having the participant run the experiment more than once, even more conditions are possible.
  • Conditions: There are many variations of the basic stimulus strings including congruent words, incongruent words, words backwards, strings of X's and words with part of the letters replaced with x's or in random order. Test how these variations affect the Stroop effect.
  • Colors to use: from red, green, blue, yellow, purple and orange.
  • Respond to either the color or the word.
  • Number of words in the condition.

Data Analyses

If you just have two conditions, you can use a t-test to analyze the results. However, if you have more conditions, you would need to do an analysis of variance (ANOVA). It would be a within subjects design unless you group your subjects in some way, such as by gender, which would make it a mixed design.


One straight forward application might be to examine differences in education, age, and gender on the Stroop. Traditionally gender has played little role in Stroop research but there has been some evidence that education and age are relevant to Stroop results (Van der Elst, Van Boxtel, Van Breukelen, & Jolles (2006). It might be interesting to speculate on why some person variables are important and others are not.

Data Format & Download


  Stroop study datafld
Figure 1

Column A provides the class ID so that different classes can select just the data from their class. Column B provides the participant ID number that each person receives upon completion of the experiment. Column C is the number of the trial in the experiment. Column D indicates the condition (incW : incongruent words; conW : congruent words; XXXX : string of X's; WordW : word in white; ConR : congruent word reversed; IncR incongruent word reversed; BCon : beginning of word correct, rest x's, congruent; BInc : same as last but incongruent; ECon : end of word correct, rest x's, congruent; EInc : same as last incongruent; MRCon: middle of word random, rest correct, congruent; MRInc : same as last incongruent; ERCon : end of word random, rest correct, congruent; ERInc : same as last incongruent; BRCon : beginning of word random, rest correct, congruent; BRInc : same as last incongruent). Column E indicates where the participant is to respond to the word or the color. Column F gives the stimulus word. Column G indicates the color of the stimulus giving the first letter of the color. Column H gives the response of the person with the first letter of the color or word depending upon what the person is to respond to. Column I gives the reaction time in milliseconds.


Lien, M.-C. & Proctor, R. W. (2002).  Stimulus-response compatibility and psychological
	 refractory period effects: Implications for response selection.  Psychonomic 
	 Bulletin & Review, 9(2), 212-	238.

Marmurek, H. H. C. (2003).  Coloring only a single letter does not eliminate 
	color-word interference in a vocal-response Stroop task: Automaticity 
	revealed.  Journal of General Psychology, 130(2), 207-224.

Stroop, J. R. (1992). Studies of interference in serial verbal reactions. 
	Journal of Experimental Psychology: General, 121, 15-23. (Original 
	work published in 1935).

Van der Elst, W., Van Boxtel, M. P. J., Van Breukelen, G. J. P., Jolles, J. (2006). 
	The Stroop color-word test: Influence of age, sex, and education; and normative
	data for a large sample across the adult age range. Assessment, 13(1), 62-79.