General Experimental Psychology
Stroop Effect Laboratory


The primary purposes of the lab are to replicate and investigate the Stroop Effect. Along the way, though, you will hopefully learn about the related topics of automatic mental processes and response times as a dependent variable.


The Stroop effect was first described in 1935 by the scientist whose name it now bears. Generally, the Stroop effect refers to the difficulty observers have in eliminating meaningful but conflicting information from a task, even when that information is irrelevant or counterproductive in that task. The Stroop effect can be manifest as │interference,▓ that is, when one mental operation degrades the performance of another.

The Stroop Effect can also be manifest as │facilitation,▓ that is, when one mental operation enhances the performance of another. The classic demonstration of the Stroop effect is produced when one tries to name the color of the ink in which a word is printed when the word itself is the name of a color other than that of the ink (Reed, 1988). Typically, one is slower in this situation than if the word is not a color term. This form of Stroop interference is thought to be evidence for the automatic nature of reading. │Automatic▓ in this context refers to an activity, such as reading, that is so well learned that it is occurs even when one attempts to suppress it (Reed, 1988). The interference probably arises when different words in the mental lexicon representing the color terms are activated by both the words and the ink color and │compete▓ with one another, slowing the overt response.

Present experiment.

In this lab, we will try to do the following:

  1. Replicate the basic Stroop effect.
  2. Determine whether the effect can be made smaller by interfering with the reading of words.
  3. Write a complete lab report and submit it.


As in some of the previous experiments, students in a lab should first pair off into different pairs, and the members of each pair should take turns acting as subject and experimenter. The stimuli are three lists of words printed in different colors. Each list represents three different experimental conditions that vary in the relationship between the words themselves and the color of the ink. Each list is labeled, indicating which experimental condition it represents:

  1. Control (Non-color words) - The words are not color terms, or even words at all.
  2. Congruent (Same color words) - The words are color terms that match the color of the ink in which they are printed.
  3. Conflicting (Different color words) - The words are color terms that do not match the color of the ink in which they are printed.

In order to conduct the experiment, a program called │stroop▓ should be started by double-clicking on it╣s icon. Once it starts, it will show the instructions in a window. After reading through the instructions, the experimenter and participant should follow them. That is, the experimenter should determine a randomized list of experimental conditions, preceeded by practice, and write these conditions on the left margin of a piece of paper. On each trial, the experimenter should tell the participant the condition, so that the participant can selec tthe condition from the list of buttons on the screen. The experimenter should also check the particpant╣s accuracy of color naming, and make sure the particpant corrects themselves before proceeding. Finally, the experimenter should record the color naming times on the piece of paper after each trial.

In the experiment, each participant will be presented with each stimulus on two occasions, once in their in their normal orientation, such that the words are │right side up,▓ and once │inverted,▓ such that the words are upside down. On each trial, the participant should name the colors of the │ink▓ of each item, naming from top to bbottom, and left column first. They should name the ink colors as rapidly and as accurately as possible, and try to ignore the written words. A random ordering for an entire experiment, to be used on a single subject, might be the following:

Trial Condition Practice Practice

  1. Neutral - Inverted
  2. Congruent - Normal
  3. Conflicting - Normal
  4. Conflicting - Inverted
  5. Congruent - Inverted
  6. Neutral - Normal

After all students have been tested, the data for the entire lab group should be entered on a summary sheet on each computer. Then complete the following data analysis steps (the last three correspond to the questions/issues proposed above):

  1. You should then first calculate mean color naming times from all the raw data. These are automatically calculated by the spreadsheet. These means can then be combined in the different ways described below. These comparisons are also calculated automatically be the spreadsheet. You should also construct a graph that will be referred to as Figure 1 in the lab report.

  2. To determine whether the basic Stroop effect was observed, you should compare the following mean color naming times:

    • Stroop Interferencenormal = RTconflicting/normal - RTneutral/normal
    • Stroop Facilitationnormal = RTcongruent/normal - RTneutral/normal
    If the Interference value is positive, then you╣ve replicated the basic Stroop interference effect. If the Facilitation value is negative, then you╣ve replicated the basic Stroop facilitation effect.

  3. To determine whether the magnitude of the Stroop effect is made smaller by interfering with the reading of words (inverting the stimuli), first calculate the same comparisons as for step 2 above, except use the means for the backwards conditions:

    • Stroop Interferenceinverted = RTconflicting/inverted - RTneutral/inverted
    • Stroop Facilitationinverted= RTcongruent/inverted - RTneutral/inverted

Compare these to the means for the inverted stimuli to those for the Normal stimuli. If the Interference and Facilitation differences (as calculated in Step 3 here) are smaller than the corresponding differences for the Normal stimuli (as calculated in Step 2 above), then you have evidence that interfering with the reading of the words reduces the size of the Stroop effect. Review the general form of a lab report, described in │Tips for Writing a Lab Report,▓ and then write a lab report in the specific form described in the next section of this handout.

The Present Lab Report.

You should write a complete lab report, from title page to figure. The following tips and ideas should help you. You should elaborate on items listed below.






Refer to Reed article

Figure caption


Insert the one made with the Excel spreadsheet