Four cards, not three, and no yellow
Stroop started from the Woodworth–Wells colour sheet but changed it on his adviser Joseph Peterson's advice. Black was needed for the plain word card, and yellow was hard to print as strongly as the rest. Both were replaced by brown and purple.
Work along the line; the clock times the whole strip
Stroop timed whole sheets, not single trials. Pick a card, press start, and click the answer for each item in order. A wrong click must be corrected before you move on, as his instructions required.
The interference ran one way
Experiment 1's card means are not printed in the summary; the bars use the 2.3-second, 5.6% difference it reports, which puts the black-ink card near 41 seconds. Uncorrected errors in Experiment 2 were charged at twice the subject's average time per word, a rule Stroop called "arbitrary" but justified.
Fourteen test days: practise ignoring the word, then try reading again
Thirty-two volunteers, each tested alone by Stroop at the same time each day; two who broke the schedule were dropped. Each day's score was the average of four half-sheets. Click a day.
Stroop said training. Later work broke the simplest version of that idea
Stroop's own conclusion: a word had one trained response, to be read, while a colour invited many (“to admire,” “to name,” “to reach for,” “to avoid”). Pick an account to see what supports or undercuts it.
Cattell had shown in his 1886 dissertation that words are read faster than colours or objects are named, and put it down to practice. The colour-word effect itself was first published in German by Erich Jaensch in 1929. Stroop's version won out through its controls and clarity.
There was almost no follow-up until the 1960s, when Klein's 1964 card study and computer-timed single trials revived it. MacLeod's 1991 review covered half a century of work. Later variants include picture–word, arrow-direction, counting, flanker and emotional versions.
Born near Murfreesboro, Tennessee. Lipscomb 1921, Peabody BS 1924 and MS 1925, then a doctorate under Peterson. He wrote only two more colour-word papers, the last in 1938. He was registrar at David Lipscomb College for eleven years, chaired its psychology department 1948–64, and wrote books on scripture until his death in Nashville.
Sources cited on this page
- [1]Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662.Classics in the History of PsychologyUsed for: Materials, subjects, procedure, all 1935 figures, quotes, Experiment 3 schedule.
- [2]Stroop (1935), DOI record.doiUsed for: Citation details.
- [3]MacLeod, C. M. (1991). John Ridley Stroop: Creator of a landmark cognitive task. Canadian Psychology, 32(3), 521–524.doiUsed for: Biography (via Wikipedia summary).
- [4]Wikipedia. John Ridley Stroop.en.wikipedia.orgUsed for: Dates, degrees, career, later papers.
- [5]MacLeod, C. M. (2015). The Stroop effect. In Encyclopedia of Color Science and Technology. Springer.author copy (PDF)Used for: Cattell 1886, thirty-year gap, Klein 1964 gradient, variants, speed-of-processing evidence, current models, brain regions.
- [6]MacLeod, C. M., & Dunbar, K. (1988). Training and Stroop-like interference. JEP: LMC, 14, 126–135.doiUsed for: Training evidence (via [5]).
- [7]MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163–203.doiUsed for: Review of later research.
- [8]Wikipedia. Stroop effect.en.wikipedia.orgUsed for: Jaensch 1929 priority.
- [9]Klein, G. S. (1964). Semantic power measured through the interference of words with color-naming. American Journal of Psychology, 77, 576–588.summarised in [5]Used for: Gradient of interference (via [5]).
- [10]Williams, J. M. G., Mathews, A., & MacLeod, C. (1996). The emotional Stroop task and psychopathology. Psychological Bulletin, 120, 3–24.doiUsed for: Emotional variant.
What changed in this revision
The 1935 paper was read in full in the Classics in the History of Psychology transcription; its tables are not reproduced there, so only figures given in the text are used. In Experiment 3 the colour-only card used a hooked-cross printer's figure in place of squares, so white showed inside the colour as it does in a printed word.
- REMOVED“The most-cited cognitive test in psychology” and “measuring executive function.” No source given; the 1935 paper frames it as associative interference and training.
- CORRECTED“The original three-condition design.” 1935 used four cards across two experiments plus a 14-day practice study, with five colours including brown and purple, not yellow.
- REMOVEDThe clinical list (ADHD, schizophrenia, Alzheimer's, TBI) and a D-KEFS mention, none sourced. Variants are now the ones MacLeod documents.
- CORRECTEDThe playable now matches 1935: serial strips, five colours, forced correction, all four cards, compared with Stroop's per-item rates.
- ADDEDCard reconstructions, materials rules, Experiment 1–2 results, the 14-day schedule, accounts from 1886 to 2003, the Klein gradient, before/after context, Stroop's biography and 10 references.
- KEPTThe note that clicking adds motor time, so compare percentages rather than raw times.
Related historical tests
Stroop's starting point was Cattell's finding that words are read faster than colours are named. Cattell blamed practice, the same account Stroop tested. The Cattell page covers his broader programme of timed laboratory tests.
Kraepelin also charted how speed changed with practice across sessions. Stroop's Experiment 3 produced a similar learning curve, and he compared it to curves from other learning experiments.
Bourdon's sheets, like Stroop's cards, were whole pages worked against the clock rather than single timed trials. Both measured attention as speed and accuracy over a long serial run.
Trail Making B, like the Stroop card, makes a well-practised sequence fight an instruction. Both later moved from research into neuropsychological batteries, long after their authors' original aims.
The WCST asks people to drop a sorting rule they have just learned. Stroop's Experiment 3 built a new habit and then measured how it fought the old one on day 13.
The d2 arrived just as Stroop research revived in the 1960s. It keeps the 1935 format of a full printed sheet worked line by line under time pressure.