The Stroop test measures how well you can focus on one feature of something while ignoring a conflicting one. You're shown color words — like the word RED printed in blue ink — and your job is to name the ink color, not read the word. Because reading is automatic, the mismatched word fights your answer and slows you down on the conflicting (incongruent) trials. That slowdown is the Stroop effect, first described by John Ridley Stroop in 1935. This free online version times your congruent and incongruent trials and reports the difference in milliseconds — a hands-on demonstration of selective attention. It's a for-fun cognitive task, not a clinical or IQ test.
Selective attention · interactive test
Stroop Test
Choose the ink color while ignoring the written word. Compare your speed and accuracy across matching and conflicting colors.
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How the Stroop test works
1. Name the ink, not the word
A color word appears in colored ink. Tap the button for the INK color — ignore what the word says. When the word and ink match (RED in red), that's a congruent trial; when they clash (RED in blue), it's incongruent.
2. Go as fast as you can
We time each answer in milliseconds. Speed matters: the test works by catching the small extra time your brain needs to override the automatic urge to read the word instead of naming its color.
3. Your interference score
At the end we compare your average time on incongruent trials with congruent ones. The difference — the Stroop effect — is how much the conflicting word slowed you down. Almost everyone shows some; a larger gap just means reading pulled at your answer more strongly this run.
What is the Stroop effect?
The Stroop effect is the well-known finding that people are slower to name the ink color of a word when the word spells a different color — for example, the word RED printed in blue. Reading is automatic for literate adults, so the written word interferes with naming the color, and the brain has to suppress the reading response. The task was introduced by John Ridley Stroop in 1935 and is now one of the most widely used measures of selective attention and cognitive control in psychology.
What this test can and cannot tell you
It's a real cognitive task. You actually perform the Stroop task and see your own interference effect — the slowdown when a word fights the ink color. That response is yours; it can't be produced for you.
The exact milliseconds are relative. Your device, browser, and how you tap add a small fixed delay, and a short run is noisy. Compare your own attempts rather than reading the absolute number as definitive.
It's not an IQ or medical test. It measures selective attention and response inhibition, not intelligence, and can't diagnose anything on an uncalibrated setup. Color vision matters too — if you might be color blind, check with our color blind test first.
Concerned about attention or memory? A casual online task can't assess that. If you have real concerns, speak with a healthcare professional who can use validated assessments.
Stroop test — frequently asked questions
- What is the Stroop test?
- The Stroop test is a classic psychology task that measures selective attention and cognitive control. You see color words printed in different ink colors and must name the ink color while ignoring the word itself. It was introduced by John Ridley Stroop in 1935 and is one of the most widely used tasks in cognitive science.
- What is the Stroop effect?
- The Stroop effect is the finding that people are slower and more error-prone at naming an ink color when the word spells a different color (for example, the word GREEN printed in red) than when the word and color match. It happens because reading is so automatic that the written word interferes with naming the color, and your brain has to suppress the reading response.
- Why does the Stroop effect happen?
- Reading is an overlearned, automatic process for literate adults — you can't easily switch it off. When the word and ink color conflict, the automatic reading response competes with the slower, deliberate task of naming the color, so it takes extra time and effort to give the right answer. This conflict and the control needed to resolve it are what the test reveals.
- What is a good Stroop test score?
- There's no pass or fail. The key number is your interference: your average time on incongruent (mismatched) trials minus your average on congruent (matched) trials. Almost everyone is slower on incongruent trials — the effect is robust and universal — so a difference of tens to a couple hundred milliseconds is normal. Use it to compare your own runs, not to rank yourself against others.
- Does the Stroop test measure IQ or detect a medical condition?
- No. It measures selective attention and the ability to inhibit an automatic response, not intelligence. Clinicians do use formal versions of the Stroop task in research and assessment, but this online version is a for-fun demonstration on an uncalibrated setup — it can't diagnose anything. If you have concerns about attention or memory, speak with a healthcare professional.
- Does color blindness affect the Stroop test?
- It can. The classic Stroop test relies on telling ink colors apart, so red-green color vision deficiency can make some ink colors harder to name and skew the result. We use four distinct colors with labeled buttons to reduce this, but if you're color blind, the score may not reflect your attention fairly. You can check your color vision with our color blind test.