Visual mismatch negativity is more than the sum of microsequences.

Visual mismatch negativity (vMMN), the difference between the event-related potentials (ERPs) to repeated (standard) events and changing (deviant) events, can be caused either by diminished activity to the repeated ones (stimulus-specific adaptation, SSA), increased activity to the new ones, or both effects. To determine which of these effects contribute to the emergence of vMMN, we investigated the effect of repetition on visual ERPs. To this end, we measured electrical brain activity to task-irrelevant stimuli both in case of stimulus onset (continuously present objects, ON-events) and stimulus offset (frequently or infrequently disappearing parts of the objects, OFF-events). We examined ERPs to changing events ("deviants"), first and second repetitions ("standards") and to changing events preceded by one, two or three different events in non-oddball (50 % deviant frequency) sequences along with ERPs to similar deviant and standard events in oddball (12,5 % deviant frequency) sequences. The absence of exogenous N1 adaptation (i.e., adaptation of the negativity in the range of putative deviant minus standard difference) in non-oddball sequences coupled with the emergence of vMMN in oddball sequences proves that vMMN can be considered more than pure stimulus-specific adaptation effect.