The effects of positions on deviant processing in mostly incompatible blocks in the flanker task.

It is assumed that focused attention is induced by mostly incompatible (MI) blocks in the flanker task. This study aimed to examine the differences in deviant processing between positions of a stimulus in MI blocks. Thirty-nine adults participated in this study. Compatible and incompatible stimuli were classified into three types: typical (central and surrounding colors: black), central-deviant (central: red; surrounding: black), and surrounding-deviant (central: black; surrounding: red). Rare and equiprobable conditions were set for MI blocks. Central- and surrounding-deviant stimuli were presented with low probabilities in the rare condition and with identical probabilities to that of typical stimuli in the equiprobable condition. Deviant processing was evaluated by comparing between event-related potentials in rare and equiprobable conditions. The posterior negativity from 120 to 170 ms (i.e., N1) for central-deviant stimuli was significantly more negative in the rare condition than in the equiprobable condition, whereas there was no difference for surrounding-deviant stimuli. Conversely, the posterior negativity from 180 to 230 ms for both stimuli was significantly more negative in the rare condition than in the equiprobable condition, and the difference (i.e., visual mismatch negativity) was similar in central- and surrounding-deviant stimuli. These findings suggest that focused attention induced by MI blocks leads to differences in deviant processing between central and surrounding areas during the N1 time range. Therefore, evaluations of deviant processing can help examine processing in central and surrounding areas independently and are valuable for understanding cognitive control mechanisms in the flanker tasks.