Proportion compatibility effects on visual mismatch negativity in a flanker task

Proportion compatibility effects, in which task performance for compatible stimuli is improved in blocks consisting of mostly compatible stimuli (MC blocks) and task performance for incompatible stimuli is improved in blocks consisting of mostly incompatible stimuli (MI blocks), are common in interference tasks. This study addressed proportion compatibility effects on visual mismatch negativity (VMMN) in the flanker task, which consisted of compatible, incompatible, and deviant stimuli. Compatible and incompatible stimuli were arrays of five black arrows. Deviant stimuli were created by the black central arrow and red surroundings of equal signs. The flanker task was conducted in MC and MI blocks, and blocks with an equal probability (EP blocks) of compatible, incompatible, and deviant stimuli. The posterior negativity from 200 to 250 ms for deviant stimuli was significantly more negative in the MC than in the EP blocks. However, there was no difference in the posterior negativity from 200 to 250 ms between MI and EP blocks. These results indicate that VMMN for deviant stimuli was observed in the MC blocks but not in the MI blocks. In addition, the posterior negativity for incompatible stimuli was modulated by the probability of incompatible stimuli. In contrast, modulation by the probability was not found in the posterior negativity for compatible stimuli. The results indicate that VMMN was elicited by incompatible stimuli but not by compatible stimuli. These findings suggest that proactive control in the MI blocks may attenuate processing in an irrelevant visual field.