Stroop color-word interference 1935
Naming the ink color of a color word printed in a conflicting color is much slower than naming plain color patches, while reading the same words is barely affected.
Main paper: Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662. https://doi.org/10.1037/h0054651
The question
Does reading a word interfere with naming the color it is printed in, and does color interfere with reading?
Design: experiment
The researchers set the conditions and compare outcomes between or within groups. Each profile says whether participants were randomly assigned.
A within-person comparison: the same participants did easier and harder versions of the task, with the order of versions arranged to address practice and fatigue. No separate groups were needed for the main contrast.
Baseline
- Name solid color patches
Result reportedFaster
Conflict
- Name the ink of a color word printed in another color
Result reportedSlower
Original diagram drawn for this site from the descriptions in the sources. It is a simplified summary, not a figure from the paper.
Procedure
Stroop reported three experiments with college students. In the first, participants read color names printed in black ink and then read color names printed in conflicting colors. In the second, they named the ink color of conflicting color words and, as a comparison, named solid colored squares. The third had a smaller group practice the conflicting-ink naming task over eight days.
The measure was the time to complete a fixed list of responses. The comparison was always the same person doing an easier version of the task.
Findings
Reading the conflicting words took only slightly longer than reading the black words, a difference Stroop judged unreliable. Naming the ink color of conflicting words was a different matter: the reported mean time for 100 responses rose from about 63 seconds for squares to about 110 seconds for conflicting words, roughly 74 percent longer.
In the practice experiment, interference shrank with practice but did not disappear.
Interpretation
Stroop explained the asymmetry by training: years of reading build stronger word-response associations than color-naming associations, so the word competes with the color response but not the reverse. Which stages of processing produce the delay is a separate question that this paper does not settle.
Limits on what it shows
- The samples were college students, and the paper is a 1935 report with the reporting conventions of its time.
- A list-timing measure shows slowing overall. It does not show which items or which processing stage caused it.
- The label 'Stroop effect' now covers many task variants, so findings from one version do not automatically apply to another.
- The experiment shows interference under these task instructions. It does not show that reading is involuntary in every situation.
Ethics
The tasks were timed reading and naming, with little risk to participants. Informed consent and the right to stop, which current research practice expects, were not described as part of the 1935 report.
Replication and reassessment
The task has become a family of procedures with different stimuli, languages and instructions. The original time difference is not a universal benchmark. Explaining interference also requires distinguishing word processing from the selection of a spoken response.
Think it through. An original practice question written for this site.
A bilingual reader names ink colors in a second language they read slowly. What would you predict about the slowing, and which comparison would test your prediction?
Show a way to reason about it
Reasoning from the training account, weaker reading in the second language means a weaker word response, so less interference is expected. A fair test compares the same readers on their stronger and weaker language, with matched word lists. This is a prediction exercise, not a reported result.
Nothing you think or select here is recorded.
Textbook connection
OpenStax Psychology 2e, 5.1 Sensation versus Perception
Related context on attention. The section does not describe this 1935 paper.
Sources and access scope
Each label says how much of the source was opened while preparing this profile. An unopened source is listed so the claim can be checked, not because it was read.
- Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020). Psychology 2e. OpenStax. https://openstax.org/books/psychology-2e/pages/5-1-sensation-versus-perceptionTextbook contextSelected textbook passages inspected
Textbook context. The Stroop effect appears here as related context on attention, not as a section about this paper.
- Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662. https://doi.org/10.1037/h0054651Consulted sourceOriginal researchSelected full-text sections inspected
Classics in the History of Psychology (York University) reproduction. Participant counts, task versions and the 63 and 110 second figures come from sections inspected with page tools.