Neural correlates of cognitive control and conflict detection in the Stroop and digit-location tasks.

In two experiments, event-related brain potentials were used to examine the neural correlates of cognitive control and conflict processing in the Stroop and digit-location tasks. The relevant dimension was cued on a trial-by-trial basis before stimulus onset. This method allows one to dissociate modulations of the event-related brain potentials (ERPs) associated with cognitive control from modulations of the ERPs associated with conflict processing that are temporally confounded in the standard Stroop task. Cognitive control was associated with a slow wave over the occipital-parietal region that differentiated goal-compatible from goal-incompatible responses in both the Stroop and digit-location tasks. Conflict processing was associated with a N450, in the Stroop task, and a conflict sustained potential (SP) in both tasks. The amplitude of the N450 was similar for color naming and word reading trials. The character of the conflict SP varied over the frontal and central-parietal regions. Over the left lateral frontal region the conflict SP was similar in amplitude across type of response in the Stroop and digit-location tasks. Over the right lateral frontal region the conflict SP was greater in amplitude for the less dominant stimulus dimension (i.e. color or digit). The findings of these experiments clearly demonstrate that different neural systems support cognitive control and conflict processing, with some degree of hemispheric specialization observed for conflict processing.