Overview
The Stroop effect is the delay in reaction time between neutral and incongruent stimuli: naming the font color of a word such as red printed in blue takes longer and produces more errors. It is named after John Ridley Stroop, who published it in English in 1935; E. R. Jaensch had published it in Germany in 1929. Modern tasks compare congruent, incongruent and neutral conditions, and the Stroop test is widely used to assess attention and inhibitory control. Related: Zeigarnik effect.
Original 1935 results
In Stroop's experiments, reading colour words printed in conflicting ink colours took only about 2.3 s longer per 100 words than reading them in black. Naming the ink colour of conflicting words, however, took much longer than naming colour patches: the mean time for 100 responses rose from 63.3 s to 110.3 s, an increase of about 74%.
| Condition | Example | Effect on colour naming |
|---|---|---|
| Congruent | "RED" in red ink | Little or none; can be faster |
| Neutral | Colour patch or XXXX | Baseline |
| Incongruent | "RED" in blue ink | Slower, more errors |
Explanations
Classic accounts include relative speed of processing (words are read faster than colours are named), automaticity (reading is hard to suppress), and the parallel distributed processing model of Cohen, Dunbar and McClelland (1990), in which pathway strength and attentional control produce the interference. MacLeod's 1991 review concluded that no single account explains all findings.
Variants
Variants include the emotional Stroop task (used in anxiety research), the numerical Stroop task (number value versus physical size) the spatial Stroop task (arrow direction versus location) and the reverse Stroop effect described by Durgin (2000), in which pointing to the colour named by a word is slowed by an incongruent ink colour.
Frequently asked questions
- Why does it happen?
- Reading is highly automatic, so the word meaning interferes with naming the color.
References
- Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662.
- Jaensch, E. R. (1929). Grundformen menschlichen Seins. Berlin: Otto Elsner.
- MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163–203.
- Scarpina, F., & Tagini, S. (2017). The Stroop Color and Word Test. Frontiers in Psychology, 8, 557.
- 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.
- Durgin, F. H. (2000). The reverse Stroop effect. Psychonomic Bulletin & Review, 7(1), 121–125.