P300 and response time from a manual Stroop task

Objectives: Manual response time (RT) and P300 event-related potential (ERP) measures were recorded in a Stroop color naming task to determine if previous results with vocal responses would be obtained using an arbitrary stimulus-response (S-R) mapping. Methods: Subjects (n=32) were instructed to respond to the display color of a word but to ignore its meaning. Display color was congruent, neutral, or incongruent with word meaning. Results: Stroop facilitation and interference effects were observed, as RT was shortest in the congruent condition, intermediate in the neutral condition, and longest in the incongruent condition. In contrast, P300 latency did not vary across color/word congruence conditions, suggesting that the RT difference between congruence conditions originated after stimulus evaluation. Conclusions: These manual RT/P300 findings support the view that Stroop interference and facilitation originate from response competition between the relevant and irrelevant stimulus attributes. By employing an arbitrary mapping of color words onto buttons, the present results indicate that the disparate effects of Stroop stimuli on RT and P300 latency do not depend on the nature of the S-R translation.