Re-thinking Stroop

What does the Stroop test mean? Congruency vs contingency.

If you’re familiar with psychology, you know the Stroop (1935) test. The general theory behind it is that participants take longer to identify the print color of a word if it is incongruent to the color word. For example, it takes us longer to read the word blue if it is written in green pixels and vice versa.

Numerous experiments have shown that the magnitude of the ‘Stroop effect’ can be manipulated by changing the proportion of trials where the words are congruent (i.e. are the same color as the words themselves, e.g. blue). When a participant does finally encounter an incongruent word (yellow), the effect is more drastic. In many scientists' minds, this difficulty arises because of the discrepancy between the meaning of the word and its color.

An alternative explanation comes in the form of the contingency hypothesis. The idea being that we implicitly learn associations between words and responses, then use these to predict how we respond to each distracting word. It’s not color that matters, just the frequency with which a word and a color are paired (Schmidt et al, 2007).

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Bolstering their point, studies have shown that Stroop effects exist when using non-color words. What was important, the authors suggest, was the frequency with which a word was paired with the color, rather than the natural congruency between the color and the meaning of the word.

But Schmidt and company took this a step further. They argued that the cognitive processes underlying contingency learning could be non-conscious. So in their experiments, participants were shown three arbitrary display words (seven, glide, chair) and two display colors of blue and green. Some words were paired with certain colors more than other colors. In this case, colors were more quickly identified in high contingency trials (words and colors that were frequently paired) than medium and low contingency trials. This effect was true even though participants could not consciously identify which words and colors were more frequently paired.

The authors propose that a major interpretation for the Stroop test may have been in error, and that we shouldn’t look at the Stroop effect as a phenomenon that occurs because of mismatches or color at all, but instead as a matter of frequency and learned response.

References
- Botvinick, M. M., Braver, T. S., Barch, D. M., Carter, C. S., & Cohen, J. D. (2001). Conflict monitoring and cognitive control. Psychological Review, 108, 624–652.

- Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18, 643–662. Received June

- Schmidt, J. R., Crump, M. J. C., Cheesman, J., & Besner, D. (2007). Contingency learning without awareness: Evidence for implicit control. Consciousness and Cognition, 16, 421–435.

- Lowe, D. G., & Mitterer, J. O. (1982). Selective and divided attention in a Stroop task. Canadian Journal of Psychology, 36, 684–700.

- Jacoby, L. L., Lindsay, D. S., & Hessels, S. (2003). Item-specific control of automatic processes: Stroop process dissociations. Psychonomic Bulletin & Review, 10, 634–644.

- Lindsay, D. S., & Jacoby, L. L. (1994). Stroop process dissociations: The relationship between facilitation and interference. Journal of Experimental Psychology: Human Perception and Performance, 20, 219–234.