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What Conflicting Mental Tasks Reveal About Thinking: The Stroop Effect

Difficulty
Time Required Long (2-4 weeks)
Prerequisites For ISEF-affiliated science fairs, studies involving human subjects require prior approval. For more information, see Projects Involving Human Subjects.
Material Availability Readily available
Cost Very Low (under $20)
Safety No issues

Abstract

Can you pat your head with one hand while you rub your stomach with the other? This experiment is kind of like that, but it can actually give you some insight into how your mind works. The task is to name colors. It sounds simple enough, but see what happens when color words get in the way.

Objective

The goal of this project is to investigate the Stroop effect: when you try to name the color in which color words are printed, it takes longer when the color word differs from the ink color than when the color word is the same as the ink color.

Credits

Andrew Olson, Ph.D., Science Buddies

Sources

  • Chudler, E. et al., 2006. "Neuroscience for Kids: Stroop Effect," Neuroscience for Kids, University of Washington, Seattle [accessed May 1, 2007] http://faculty.washington.edu/chudler/words.html.
  • APA, 2007. "Interference: The Stroop Effect," American Psychological Association [accessed May 1, 2007] http://www.apa.org/science/stroop.html.
  • Stroop, J.R., 1935. "Studies of Interference in Serial Verbal Reactions," originally published in Journal of Experimental Psychology 18: 643-662, available online from Classics in the History of Psychology, York University, Toronto, Ontario [accessed May 1, 2007] http://psychclassics.yorku.ca/Stroop/.

Cite This Page

MLA Style

Science Buddies Staff. "What Conflicting Mental Tasks Reveal About Thinking: The Stroop Effect" Science Buddies. Science Buddies, 30 June 2014. Web. 1 Sep. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/HumBeh_p027.shtml>

APA Style

Science Buddies Staff. (2014, June 30). What Conflicting Mental Tasks Reveal About Thinking: The Stroop Effect. Retrieved September 1, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/HumBeh_p027.shtml

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Last edit date: 2014-06-30

Introduction

The experiment described in this project is an attempt to unravel the workings of thought processes that involve attention, perception, reading, and naming. To give you an idea of how the experiment works, here is a task for you to try:

  1. Following this list of instructions are two gray boxes that each contain a list of words.
  2. The words appear in color on your screen.
  3. The task is to name the color of the letters of each word (not to read the words).
  4. Try to the name each color as quickly as possible.


red green blue yellow black white yellow blue black green white red


white black yellow green blue red black yellow white blue green red

Naming the colors was much harder for the second box, right? You may even have felt like you were fighting back an urge to read the color word out loud, rather than naming the color of the letters. Do you get the feeling that it takes longer to name the printed colors when the color word is different than the printed color? In this experiment, you will time responses from many volunteers in order to find out if this is the case.

This phenomenon was described in 1935 in a now-famous paper by John Ridley Stroop, and is known in experimental psychology as the Stroop effect. One explanation for the Stroop effect is called interference. From the earliest years of school, reading is a task that people practice every day. We become so good at it that we read words automatically. When we are asked to name the color of the word instead of reading the word, somehow the automatic reading of the word interferes with naming the color of the word.

The interference effect provides scientists with a measurable means to investigate how the brain works. By manipulating the stimuli used for the test in various ways, you can find out what types of thinking tasks interfere with other thinking tasks. For example, if you used nonsense strings of letters instead of color words, would there still be interference? Probably not. What if you scrambled the letters of the color words, or misspelled them, or bent them into circles? Each of these manipulations could help you to measure how easily people can read words, even when the words are not presented properly. If the interference effect persists, then you know that the manipulation did not affect the subjects' ability to read the words. You can also see if the Stroop effect occurs with non-color naming tasks: for example, naming shapes. The Variations section has some suggestions to get you started if you want to expand further on this project. You can also have a great project by repeating Stroop's classic experiment, as described in the Experimental Procedure section, below.

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:

  • Attention
  • Perception
  • Interference
  • Anterior cingulate gyrus
  • Cognitive psychology

Questions

  • How does the concept of interference help to explain the Stroop effect?

Bibliography

  • Try these webpages for background information on the Stroop effect:
  • This article from Science News shows how Stroop's experimental work from 1935 has had a lasting influence on experimental psychology. You may be able to find it at your local library, or it can be purchased from Science News archives online for a modest fee:
    Bower, B., 1992. "Brother Stroop's Enduring Effect: A Mental Task Devised Nearly 60 Years Ago Still Intrigues Psychologists," Science News 141: 312-314.
  • This is the original paper, from which the Stroop effect gets its name:
    Stroop, J.R., 1935. "Studies of Interference in Serial Verbal Reactions," originally published in Journal of Experimental Psychology 18: 643-662, available online from Classics in the History of Psychology, York University, Toronto, Ontario [accessed May 1, 2007] http://psychclassics.yorku.ca/Stroop/.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

  • Computer with a color printer
  • Two sheets of cardstock (available at an office-supply store or stationer)
  • Two envelopes
  • Stopwatch
  • Volunteers to take a simple color-naming test

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Experimental Procedure

Note: for ISEF-affiliated science fairs, studies involving human subjects require prior approval. For more information, see Projects Involving Human Subjects.

  1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
  2. Click here for a pdf file (requires Adobe Acrobat) with four pages of color words that you can use for this project. Each page has the 20 sequences of five color words (red, blue, green, brown, purple) printed in pseudo-random order.
    1. Page one in the file has color words printed in matching color ink.
    2. Page two in the file has color words printed in different color ink (five examples of each different color).
    3. Note: pages three and four have the color words printed in black ink. These can be used for Variation 7, below.
    4. Print the pages you need on card stock (for sturdiness), then cut them into horizontal strips.
    5. Lightly label the backs of the strips, and keep the two sets in separate envelopes.
    6. Your volunteers will call out the ink colors as they read through the strips.
  3. For each volunteer, instruct them on what they are supposed to do in the test:
    1. You will be given cards containing a sequence of words printed in colored ink.
    2. The ink colors used are red, blue, green, brown, and purple.
    3. The task is to call out the ink color of each word as quickly as possible without making a mistake.
  4. Time how long it takes for the volunteer to name the colors of the non-matching words.
  5. Time how long it takes for the volunteer to name the colors of the matching words.
  6. For half of the volunteers, reverse the order and have them name the colors of the matching words first.
  7. Calculate the average time to name the colors for each word list.
  8. Calculate the time difference for each volunteer (i.e., non-matching word time minus the matching word time). Then calculate the average difference for the group of volunteers.
  9. Make bar graphs to illustrate your results.

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Variations

  • What if the words printed in colored ink are not color words? Does interference still occur?
  • What if you use nonsense words, i.e. random strings of characters like 'xgwrf'? Does interference still occur?
  • Does interference still occur if the test words are turned upside down or rotated 90°? Design an experiment to find out.
  • What if you use single letters? Does it matter if the letters match the first letter of the color name?
  • Another way to investigate the finding would be to look for the effect with youngsters who know their colors but don't yet know how to read. Would you expect to find the Stroop effect in this age group?
  • For an alternative experiment that investigates whether the Stroop effect occurs with shapes, see the Science Buddies project Shaping Your Thoughts?
  • A slightly different experiment would be to measure the speed for reading a list of color words printed in matching color vs. color words printed in black. What would you expect to find? Note: pages 3 and 4 of the pdf file have the color words printed in black ink. Page 3 has the words in the same order as page 1, and page 4 has the words in the same order as page 2.
  • Advanced. Another idea would be to test non-native English speakers. Perhaps reading English is not automatic for this group and the interference would not occur. As a control, you could also have them try the test with the words printed in their native language.
  • Advanced. Does practice make any difference with the Stroop effect? In other words, can people improve their times by practicing naming colors? Design an experiment to find out.
  • Advanced. Another idea for a follow-on experiment would be to see if distortions of the words (e.g., printing the letters on a circular, instead of horizontal, baseline) would decrease or eliminate the interference. See the Science Buddies project Warped Words and the Stroop Effect for details.

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