Proportion compatibility effects, in which task performance for compatible stimuli
is improved in blocks con-sisting 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.
