Behavioral and ERP indices of response conflict in Stroop and flanker tasks.

We investigated effects of different proportions of incongruent trials on behavioral and event-related potential (ERP) interference measures associated with response conflict in the Stroop and flanker task. From the literature, we hypothesized that response conflict is greater when incongruent trials are rare compared to when incongruent trials are frequent. In support, the behavioral results on both tasks and the ERP results on the Stroop task (N450) showed that interference effects were significantly larger when incongruent trials were rare than frequent. In contrast, the ERP results on the flanker task N200 showed a larger interference effect when incongruent trials were frequent than rare. Because results for the flanker N200 were opposite to behavioral effects and theoretical predictions, our findings challenge the notion of the flanker N200 as a valid index of response conflict.