What the Stroop test asks you to do
A color word appears in the middle of the screen. You choose the color it is printed in, not the color it spells. If the word RED is printed in blue, the answer is blue.
Each word has a short time limit, and a word you run out of time on is left out of the timing. Half the words match their ink and half conflict with it, and both halves use the same mix of ink colors, so the two can be compared. Levels here run from 14 to 28 words with three or four colors.
What it measures, and what it does not
It measures one narrow thing: how much a strong habit slows down a weaker one. Reading is automatic for a fluent reader. Naming a color is not. The gap between the two halves is the cost of holding the reading habit back.
That gap comes from two small samples, so treat a difference of a few tens of milliseconds as noise. The test also leans on fluent reading in the language you are using, which is why results in different languages are kept apart here.
It needs you to tell three or four inks apart. The inks differ in lightness as well as hue, but red, green and yellow can still look alike with a red-green color-vision deficiency. If they look alike to you, the score does not describe what you can do.
Where the numbers come from
J. R. Stroop published the effect in 1935. In one experiment, 100 students named the colors of 100 conflicting color words in 110.3 seconds. Naming the colors of 100 plain squares took the same students 63.3 seconds. That is an increase of 47.0 seconds, or 74.3 percent (Stroop, Journal of Experimental Psychology, 1935, hosted by York University).
The interference runs mostly one way. In a separate experiment with 70 students, reading color words printed in the wrong ink took only 2.3 seconds longer than reading them in black, or 5.6 percent. The same paper calls that increase unreliable.
Practice narrows the gap. The same paper reports a later experiment in which 32 students practiced the conflicting test for eight days and cut their time by 16.8 seconds, 33.9 percent of the first day. The interference got smaller, but it did not go away.
How to practice it here
Answer as fast as you can without guessing. Look at the middle of the word rather than reading across it. Keep the answer buttons in view, since they stay in the same order for a whole round and you can learn where they are.
Move up a level only when you can finish a round without running out of time on a word. Start with the Stroop practice. The Name the ink lesson shows the rule with a worked example. Other timed tasks are on the Attention page.
Related practices on this site
- Reaction time. The same timing without the conflict, so you can see what the conflict costs.
- Visual search. Find one named shape while the others pull at you.
- Symbol coding practice. Hold a key in mind and apply it quickly.
Questions people ask
What is the Stroop test?
In a Stroop test you name the color of the ink a word is printed in, not the word itself. When the word says one color and the ink is another, almost everyone slows down. That slowdown is the Stroop effect, which J. R. Stroop published in 1935. It shows how much a strong habit, reading, slows down a weaker one, naming a color.
What does a Stroop test score mean?
The result is the gap between your times on words that match their ink and words that conflict with it. That gap is the cost of holding back the reading habit. It comes from two small samples, so treat a difference of a few tens of milliseconds as noise. It measures one narrow thing, and results in different languages are kept apart.
How big is the Stroop effect?
In Stroop's 1935 paper, 100 students named the colors of 100 conflicting color words in 110.3 seconds. Naming the colors of 100 plain squares took the same students 63.3 seconds. That is 47.0 seconds longer, or 74.3 percent. In a separate experiment, reading color words in the wrong ink took only 2.3 seconds longer than reading them in black.
Does the Stroop effect shrink with practice?
It shrinks but does not go away. Stroop's 1935 paper reports an experiment in which 32 students practiced the conflicting test for eight days. They cut their time by 16.8 seconds, 33.9 percent of the first day. The interference was smaller at the end of those eight days, and it was still there.
Can I take a Stroop test online?
Yes. The Stroop practice on this site runs in your browser and is free: 3 rounds a day without an account, unlimited once you sign in. A round runs from 14 to 28 words with three or four colors. Half the words match their ink and half conflict with it, so the two halves can be compared. Each word has a short time limit, and a word you run out of time on is left out of the timing.
Does color blindness affect the Stroop test?
It can. The test needs you to tell three or four inks apart. The inks here differ in lightness as well as hue, but red, green and yellow can still look alike with a red-green color-vision deficiency. If the inks look alike to you, the score does not describe what you can do.