Neural time course of conflict adaptation effects on the Stroop task.

Cognitive control theory suggests conflict effects are reduced following high- relative to low-conflict trials. Such reactive adjustments in control, frequently termed "conflict adaptation effects," indicate a dynamic interplay between regulative and evaluative components of cognitive control necessary for adaptable goal-directed behavior. The current study examined conflict adaptation effects while 36 neurologically-normal participants performed a single-trial color-naming Stroop task. Trials preceded by incongruent (high conflict) and congruent (low conflict) trials were compared for behavioral (response time [RT] and error rate) and electrophysiological (N450 and conflict SP components of the event-related potential [ERP]) concomitants of cognitive control. A conflict adaptation effect was present for RTs that could not be accounted for by associative or negative priming. ERPs revealed a parietal conflict slow potential (conflict SP) that differentiated incongruent from congruent trials and monotonically differentiated current trial congruency on the basis of previous-trial context (i.e., showed conflict adaptation); the fronto-medial N450 was sensitive to current trial congruency but not to previous-trial context. Direct comparison of normalized conflict SP and N450 amplitudes showed the conflict SP was sensitive to the effects of previous-trial context, while the N450 was so to a lesser extent and in a different pattern. Findings provide clarification on the neural time course of conflict adaptation and raise further questions regarding the relative roles of the parietal conflict SP and fronto-medial N450 in conflict detection and processing.