How the Stroop Effect Works

Naming a Color but Not the Word

Yellow red green stroop effect test

The Stroop effect is a phenomenon that occurs when the name of a color doesn't match the color in which it's printed (e.g., the word "red" appears in blue text rather than red). In such a color test (aka a Stroop test or task), you'd likely take longer to name the color (and be more likely to get it wrong) than if the color of the ink matched the word.

How the Stroop Effect Works

Although it might sound simple, the Stroop effect refers to the delayed reaction times when the color of the word doesn't match the name of the word. It's easier to say the color of a word if it matches the semantic meaning of the word.

For example, if someone asked you to say the color of the word "black" that was also printed in black ink, it would be much easier to say the correct color than if it were printed in green ink.

The task demonstrates the effect that interference can have when it comes to reaction time. It was first described during the 1930s by American psychologist John Ridley Stroop for whom the phenomenon is named. His original paper describing the effect has become one of the most famous, as well as one of the most frequently cited, in the history of psychology. The effect has been replicated hundreds of times by other researchers.

For students of psychology looking for a relatively easy and interesting experiment to try on their own, replicating the Stroop effect can be a great option.

Theories of the Stroop Effect

Researchers don't yet know why words interfere with naming a color in this way, but researchers have proposed several theories:

  • Selective attention theory: According to this theory, naming the actual color of the words requires much more attention than simply reading the text.
  • Speed of processing theory: This theory states that people can read words much faster than they can name colors. The speed at which we read makes it much more difficult to name the color of the word after we've read the word.
  • Automaticity: This theory proposes that automatic reading doesn't require focused attention. Instead, the brain simply engages in it automatically. Recognizing colors, on the other hand, may be less of an automated process. While the brain registers written meaning automatically, it does require a certain amount of attentional resources to process color, making it more difficult to process color information and therefore slowing down reaction times.
  • Parallel Distributed Processing: Word recognition is an unconscious process that's better described as "contextually controlled" rather than automatic.

Other Uses of the Stroop Test

Over time, researchers have altered the Stroop test to help study populations with brain damage and mental disorders such as dementia, depression, and attention-deficit/ hyperactivity disorder (ADHD).

For example, in studying people with depression, researchers present negative words such as "grief" and pain" along with neutral words such as "paper" and "window." Typically, these people speak the color of a negative word more slowly than they do a neutral word.

Performing Your Own Stroop Test

The original Stroop test included two parts. In the first, the written color name is printed in a different color of ink, and the participant is asked to speak the written word. In the second, the participant is asked to name the ink color.

There are a number of different approaches you could take in conducting your own Stroop effect experiment.

  • Compare reaction times among different groups of participants. Have a control group say the colors of words that match their written meaning. Black would be written in black, blue written in blue, etc. Then, have another group say the colors of words that differ from their written meaning. Finally, ask a third group of participants to say the colors of random words that don't relate to colors. Then, compare your results.
  • Try the experiment with a young child who has not yet learned to read. How does the child's reaction time compare to that of an older child who has learned to read?
  • Try the experiment with uncommon color names, such as lavender or chartreuse. How do the results differ from those who were shown the standard color names?

Terms and Key Questions

Before you begin your experiment, you should understand these concepts:

  • Selective attention: This is the way we focus on a particular item for a selected period of time.
  • Control group: In an experiment, the control group doesn't receive the experimental treatment. This group is extremely important when comparing it to the experimental group to see how or if they differ. 
  • Independent variable: This is the part of an experiment that's changed. In a Stroop effect experiment, this would be the colors of the words. 
  • Dependent variable: The part of an experiment that's measured. In a Stroop effect experiment, it would be reaction times.
  • Other variables: Consider what other variables might impact reaction times and experiment with those.

Frequently Asked Questions

  • What is the Stroop test used for?

    The Stroop test helps researchers evaluate the level of your attention capacity and abilities, and how fast you can apply them. It's particularly helpful in assessing attention-deficit/hyperactivity disorder (ADHD) and executive functioning in people with traumatic brain injuries (TBIs).

  • What part of the brain does the Stroop test affect?

    The Stroop test helps researchers measure the part of the brain that handles planning, decision-making, and dealing with distraction.

  • What do my Stroop test results mean?

    There are many possible combinations of scores on the first and second tasks. They might indicate speech problems, reading skill deficits, brain injury. color blindness, emotional upset, or low intelligence. Likewise, they might mean that your brain is able to handle conflicting information well and has adequate cognitive adaptability and skills.

4 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Stroop JR. Studies of interference in serial verbal reactions. J. Exp. Psychol. Gen. 1935;18;643-662. doi:10.1037/h0054651

  2. Sahinoglu B, Dogan G. Event-Related Potentials and the Stroop EffectEurasian J Med. 2016;48(1):53‐57. doi:10.5152/eurasianjmed.2016.16012

  3. Besner D, Stolz JA. Unconsciously controlled processing: the stroop effect reconsideredPsychonomic Bulletin & Review. 1999;6(3):449-455. doi:10.3758/BF03210834

  4. Frings C, Englert J, Wentura D, Bermeitinger C. Decomposing the emotional Stroop effectQuarterly Journal of Experimental Psychology. 2010;63(1):42-49. doi:10.1080/17470210903156594

By Kendra Cherry, MSEd
Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."