Effects of S-R mapping and response modality on performance in a Stroop Task.

Forty subjects performed a choice reaction time task in which the stimulus was the word Red or Green printed in either red or green ink. Subjects responded verbally in one block of trials and by key pressing in another block. For one group, ink color was the relevant cue, and for another group, the word was the relevant cue. Half of the subjects in each group were instructed to make the response that corresponded to the relevant cue (compatible S-R [stimulus-response] mapping); the other half were instructed to make the response that did not correspond (incompatible S-R mapping). In general, subjects who performed under compatible S-R mapping instructions reacted faster when the irrelevant cue corresponded to the response than when it did not. In contrast, subjects show performed under incompatible S-R mapping instructions reacted faster when there was a lack of correspondence between the irrelevant cue and the response than when there was correspondence. Results were consistent with a notion of logical recoding; that is, that instructing subjects to recode the relevant cue into the alternate color may have caused them to recode the irrelevant cue in the same logical manner. Results might also be interpreted to suggest that the Stroop effect is related to congruence between the relevant and the irrelevant cues rather than to correspondence between the irrelevant cue and the response.