Memory-based detection of task-irrelevant visual changes.

Colored grating patterns were presented to 8 participants in a passive oddball condition (standard, 87.5% and deviant, 12.5%, differing in their color). In the corresponding multicolor condition, grating patterns of eight different colors were presented, their probabilities set equal both to each other and to that of the deviant in the oddball task. Compared with the ERP response elicited by the standard stimulus, the deviant response was negatively displaced over posterior areas, the difference wave peaking at 136 ms. A similar negative wave was obtained when the ERP response to the deviant was compared with the ERP elicited by the same stimulus in the multicolor condition. This result rules out stimulus- (color-) specific refractoriness as a major factor in the generation of the deviance-related posterior negativity. The observed posterior negativity can therefore be regarded as a visual analog of the mismatch negativity (vMMN).