🎮 How to Play
- A color word appears in a different color (e.g. the word "RED" written in blue).
- Click the button matching the color the word is written in - NOT what the word says.
- Tests selective attention. Score +1 right, -1 wrong. 30-second round.
About this test
The Stroop test asks you to name the ink colour of a word as fast as you can while ignoring what the word spells, so when RED is printed in blue you must answer blue. It is the classic laboratory demonstration that automatic reading interferes with deliberate colour naming.
Psychologist John Ridley Stroop published the effect in his 1935 doctoral work, and it has since become one of the most cited and replicated experiments in cognitive science. The interference reveals how the brain handles competing responses: reading is overlearned and fires automatically, while colour naming is slower and effortful, so the two collide whenever they disagree. Today the Stroop task is used in research on attention and ageing, in clinical screening of frontal-lobe and executive function, and as a quick brain-training drill like this 30-second version.
How it works
Trials are either congruent (word meaning matches its ink) or incongruent (they conflict). Your interference score is the extra time the conflict costs. This game pushes incongruent trials and scores accuracy under time pressure.
Stroop interference = RT(incongruent) - RT(congruent) Trial types: congruent GREEN in green -> word helps (faster) incongruent GREEN in red -> word fights (slower, more errors) This game: +1 correct, -1 wrong, 30-second round, answer the INK colour
- RT = reaction time, the milliseconds between the word appearing and your response.
- Interference = the congruent-to-incongruent gap, typically 100 to 250 ms in healthy adults.
- Inhibitory control = the executive skill of suppressing the automatic reading response; a smaller gap means stronger control.
- Score = correct answers minus errors in the time window, a rough proxy for speed and accuracy combined.
Worked example: scoring one trial
The word YELLOW appears, printed in blue ink. The four answer buttons are RED, GREEN, BLUE, YELLOW.
- Read the instinct: your brain instantly registers the meaning "yellow" - this is the automatic response you must ignore.
- Find the ink: the letters are coloured blue, so the correct answer is BLUE.
- Inhibit and respond: override the urge to press YELLOW and press BLUE instead.
- Score: a correct BLUE press adds +1; pressing YELLOW (the word) would subtract 1.
- Notice the cost: that hesitation before pressing BLUE is the Stroop interference in action, usually a fraction of a second.
Stroop conditions reference
Researchers separate the task into named conditions. This game uses the colour-word incongruent condition, the one that produces the largest interference.
| Condition | What you see | Effect on speed |
|---|---|---|
| Neutral | A non-colour word (DOG) in a colour | Baseline, no conflict |
| Congruent | RED printed in red | Slightly faster (word helps) |
| Incongruent | RED printed in blue | Slower, more errors (word fights) |
| Reverse Stroop | Name the word, ignore the ink | Little interference (reading wins) |
Common pitfalls
- Reading instead of looking. The single biggest mistake is letting your eyes read the word. Defocus slightly and attend only to the colour of the strokes.
- Racing past accuracy. Because wrong answers subtract a point, blazing speed with frequent errors scores worse than a steady, correct pace.
- Treating it as an IQ test. The Stroop measures attention and inhibition, not general intelligence; a fast score does not mean a high IQ.
- Ignoring fatigue and caffeine. Tiredness, alcohol, and even time of day shift reaction times by tens of milliseconds, so compare scores only under similar conditions.
- Colour-vision confounds. Red-green colour blindness makes some trials genuinely ambiguous; the test assumes typical colour perception.
- Over-interpreting one round. A single 30-second game is noisy. Average several rounds before drawing any conclusion about your attention.
Related tools
Frequently asked questions
What is the Stroop effect?
The Stroop effect is the delay and error increase that happens when you try to name the ink colour of a word whose meaning is a different colour, for example the word RED printed in blue. Reading is so automatic that the printed word interferes with the slower, deliberate task of naming the colour. It was first reported by John Ridley Stroop in 1935 and is one of the most replicated findings in all of experimental psychology.
Why is it harder to name the colour than to read the word?
Adults read fluent text faster and more automatically than they name colours, so the word meaning is processed before you can suppress it. When the word and the colour conflict (the incongruent condition), your brain must inhibit the dominant reading response and force through the weaker colour-naming response. That extra act of inhibition costs time, usually 100 to 250 milliseconds per item, which is the measured Stroop interference.
What does a Stroop test measure?
It measures selective attention, processing speed, and inhibitory control, the part of executive function that lets you override an automatic response. Clinicians use Stroop variants to probe frontal-lobe function and to screen for conditions that affect attention and inhibition, such as ADHD, depression, and some forms of dementia. In everyday terms, a smaller gap between your congruent and incongruent scores means stronger cognitive control.
What is the difference between congruent and incongruent trials?
A congruent trial shows a colour word printed in its own colour, such as GREEN written in green, where the word actually helps you. An incongruent trial shows a mismatch, such as GREEN written in red, where the word fights the correct answer. The Stroop interference score is the reaction-time difference between the two: incongruent trials are reliably slower and produce more errors. This trainer mixes incongruent trials to maximise that interference.
Can you train or improve your Stroop score?
Practice does shrink your reaction time on the specific task, partly because you learn to focus on the ink and partly through general familiarity. However, the underlying interference effect never fully disappears, because automatic reading cannot be switched off in a literate adult. Improvements transfer poorly to unrelated tasks, so a faster Stroop score mainly reflects better attention to this particular game rather than a broad jump in general intelligence.