Stroop Test_

Name the ink colour of each word as fast as you can — not what the word says. Then read how this 90-year-old task became one of psychology's most studied measures of attention.

What the Stroop test is

The Stroop test is one of psychology's most famous demonstrations of cognitive interference. You are shown the name of a colour printed in coloured ink and asked to name the ink colour while ignoring the word. When word and ink disagree — the word RED printed in blue — people are reliably slower and more error-prone than when the two agree. That slowdown is the Stroop effect.^1,4

The 1935 experiment

It is named after John Ridley Stroop, who reported three experiments in a 1935 paper in the Journal of Experimental Psychology. He found that naming the ink colours of mismatched colour-words took far longer than reading the words or naming plain colour patches, and he used that time difference as a measure of how strongly the irrelevant word interfered.¹ The task proved so durable that it became a cornerstone of attention research; a later integrative review catalogued roughly 400 studies spanning half a century and distilled eighteen findings any theory of the effect must explain.²

What it measures

Reading is highly practised and largely automatic, whereas naming an ink colour is comparatively effortful. The incongruent condition pits the two against each other, so doing it well means suppressing the automatic urge to read. For that reason the Stroop task is widely used as a measure of selective attention and inhibitory control — the ability to hold back a dominant response in favour of a weaker, task-relevant one.^4,2 The size of the effect is usually the reaction-time gap between incongruent and congruent (or neutral) trials.⁴

Why it happens

Two classic explanations dominated for decades: that colour and word are processed at different speeds (relative speed of processing), and that reading is automatic in a way colour-naming is not (automaticity of reading). MacLeod's review concluded that neither, on its own, captured all the evidence.² The most influential modern account is the parallel distributed processing model of Cohen, Dunbar and McClelland, which treats automaticity not as all-or-nothing but as a continuum set by how strongly a pathway has been trained — because the reading pathway is far stronger than the colour-naming one, it intrudes when the two compete.³

How it is used

A standardised version, the Stroop Colour and Word Test, is used in neuropsychology to assess the ability to inhibit cognitive interference, and is often described as a benchmark measure of executive function.⁴ Performance varies with age and education, and several competing scoring methods exist, so clinical results are interpreted against population norms rather than read as a standalone diagnosis.⁴

Variants

Researchers have built many spin-offs. In the emotional Stroop task the colour-words are replaced with emotionally charged words, and people with anxiety or related conditions tend to be slower to name the ink colour of threat-related words — a result used widely in clinical psychology, though its mechanism is debated and may differ from the classic effect.⁵

Reading your result

A normal result is simply being slower on the mismatched trials than the matching ones — that gap is the effect, and almost everyone shows it.² Bear in mind this page is a quick browser demo, not a clinical instrument: reaction times measured through a web page are affected by your device, browser, input method and surroundings, and the theory behind the task is itself still actively debated.⁶ Treat your numbers as an illustration of interference, not an assessment of your cognition.

References

1. Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662. doi.org/10.1037/h0054651
2. MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163–203. doi.org/10.1037/0033-2909.109.2.163
3. Cohen, J. D., Dunbar, K., & McClelland, J. L. (1990). On the control of automatic processes: A parallel distributed processing account of the Stroop effect. Psychological Review, 97(3), 332–361. doi.org/10.1037/0033-295X.97.3.332
4. Scarpina, F., & Tagini, S. (2017). The Stroop Color and Word Test. Frontiers in Psychology, 8, 557. doi.org/10.3389/fpsyg.2017.00557
5. Williams, J. M. G., Mathews, A., & MacLeod, C. (1996). The emotional Stroop task and psychopathology. Psychological Bulletin, 120(1), 3–24. doi.org/10.1037/0033-2909.120.1.3
6. Algom, D., & Chajut, E. (2019). Reclaiming the Stroop effect back from control to input-driven attention and perception. Frontiers in Psychology, 10, 1683. doi.org/10.3389/fpsyg.2019.01683