Quantitative relation between conflict and response inhibition in the Flanker task.

The 2001 conflict monitoring hypothesis of Botvinick and colleagues posits that the amount of conflict raised by incongruent stimuli in a flanker task affects subsequent cognitive control, such as response inhibition. The present experiment yielded empirical evidence of the quantitative relation between conflict and response inhibition. Participants judged the direction of a target arrow flanked by distractor arrows presented above and below the target. The amount of conflict was manipulated by varying the distance between the target and the directional distractors. Analysis showed that response times were longer for incongruent trials than for congruent trials, and response times on incongruent trials were longer for the small distance than for the large distance conditions. In addition, the response times in congruent trials became longer as the amount of conflict in the preceding trial increased. These results are consistent with Botvinick, et al.'s hypothesis that the conflict-detection mechanism determines the amount of response inhibition depending on the amount of conflict. Responses on incongruent trials were faster and more accurate when the preceding trial was incongruent than when it was congruent, and the size of this response facilitation was not influenced by the amount of conflict. These results suggest that the conflict detection mechanism modulates the subsequent behaviors by two forms of control which are differently affected by the amount of conflict.