Electrophysiological correlates of proportion congruency manipulation in a temporal flanker task

Response conflict evoked by a distractor stimulus object in interference tasks is associated with longer reaction times and a pronounced ERP component referred to as the fronto-central N2. Increasing the proportion congruency (PC, i.e., the proportion of trials in which target and distractor are associated with the same response) is assumed to enhance distractor-evoked conflict via defocusing of attention. Findings concerning the effect of the PC on the N2 in Eriksen flanker task experiments have been inconsistent, however, lending little support to the notion that the N2 reflects a conflict monitoring process. Here, we analyze the N2 in a temporal flanker task, in which the distractor stimuli, presented in advance of the target, elicit pronounced activation of the associated responses (as inferred from the lateralized readiness potential) when the PC is high. Consistent with result pattern obtained in other tasks involving successive presentation of the distractor and the target, conflict trials in a high-PC condition evoked a particularly large N2. These findings accord with the assumption that the N2 reflects either conflict monitoring or conflict-induced regulatory measures (i.e., reactive control). In light of the discrepancy of results obtained under conditions of simultaneous and successive distractor-target presentation, we speculate that the N2 is pronounced in situations that offer strong hints for classifying dominating response activation as incorrect, possibly reflecting particular control to counter this activation. Additional properties of the temporal flanker task, related to ERP investigations, are discussed.