Name the ink color of words that spell a conflicting color. A century-old measure of cognitive control. Click the button matching the ink color of the word — not what the word spells. The Stroop effect, first described in 1935, is one of the most replicated findings in cognitive psychology.

What the Stroop Test measures

The Stroop Test, first described by American psychologist John Ridley Stroop in 1935, measures cognitive interference — the delay in reaction time that occurs when two conflicting pieces of information are presented simultaneously. In the classic version, a word naming a color (e.g., "red") is printed in an ink color that may or may not match (e.g., the word "red" printed in green ink). The participant must name the ink color, not read the word.

Reading is such an overlearned skill in literate adults that the word's meaning is automatically activated, even when we try to ignore it. To respond correctly, you must inhibit the automatic reading response and instead attend to the ink color. This requires executive function — specifically, the ability to suppress a prepotent (dominant) response, which is a core component of cognitive control.

How your score is calculated

The game runs 20 trials. On each trial, you see a color word printed in a colored ink, and you click the button matching the ink color. The game records your reaction time (in milliseconds) and whether you were correct. At the end, you see your average reaction time on congruent trials (where the word and ink match) versus incongruent trials (where they don't). The difference between the two is your Stroop effect.

Worked example

If you see the word "RED" printed in green ink, the correct answer is "Green." Most people take ~200-400 ms longer to respond on incongruent trials than on congruent trials (where "RED" is printed in red ink). This delay is the Stroop effect.

What a typical score looks like

Published norms (MacLeod, 1991, a comprehensive review of over 50 years of Stroop research) suggest typical healthy adults show:

Congruent trial RT: ~500-700 ms
Incongruent trial RT: ~700-1000 ms
Stroop effect (difference): ~150-300 ms
Accuracy: typically above 90% on congruent trials, 80-95% on incongruent trials

Larger Stroop effects (slower incongruent responses) are associated, in the research literature, with weaker inhibitory control. The effect tends to be larger in children, in older adults, and in individuals with certain clinical conditions including ADHD and schizophrenia. It is smaller in people who have practiced the task — though, like other brain-training effects, the practice benefit is largely task-specific.

Why the Stroop Test has lasted 90 years

The Stroop Test is one of the most-used instruments in cognitive psychology for three reasons. First, the effect is large and reliably reproduced — virtually every literate adult shows it. Second, it cleanly isolates one component of executive function (response inhibition) without requiring complex instructions or equipment. Third, it is sensitive to a wide range of clinical and developmental differences, which makes it useful as a screening instrument. None of that means playing our version diagnoses anything — for clinical assessment, see a licensed neuropsychologist.

Related reading For a deeper dive into what the Stroop Test does and doesn't tell us about cognition, see our article The Stroop Test: What It Measures and How to Read Your Score.