No effects of proactive control on deviant processing in the central area in mostly compatible blocks of the flanker task

Behind the proportion compatibility effects in the flanker task, processing in the central area was hypothesized to be enhanced by proactive control in the mostly incompatible (MI) blocks compared with the mostly compatible (MC) blocks. This study aimed to examine this hypothesis and focused on deviant processing in the central area. A total of 45 adults performed the flanker task, which included central-deviant stimuli. Proportion deviance was manipulated by rare (15 %) and equiprobable (50 %) conditions in the MC and MI blocks. The color of the central and surrounding arrows was different and the same between the central-deviant and typical stimuli, respectively. Thus, deviant processing in the central area was evaluated based on a comparison of event-related potentials for the central-deviant stimuli between the rare and equiprobable conditions. The N1 difference and visual mismatch negativity for the central-deviant stimuli did not significantly differ between the MI and MC blocks. These results suggested that proactive control in the MI blocks had no effects on deviant processing in the central area, which contradicted the hypothesis. In addition, N1 for both the central-deviant and typical stimuli was significantly reduced in the MI blocks compared with the MC blocks, suggesting that the total amount of processing was reduced in the MI blocks compared with the MC blocks. These findings suggest that proactive control in the MI blocks functions to inhibit processing in the surrounding area; however, it does not enhance processing in the central area.