Event-related potentials reveal involuntary processing of orientation changes in the visual modality.

The present study investigated whether there is a visual counterpart of the auditory mismatch negativity. Event-related potentials were recorded while subjects performed a spatial frequency discrimination task. "Match" and "nonmatch" stimuli were specifically categorized according to whether the second stimulus had the same orientation as the first stimulus in each trial. Nonmatch stimuli elicited larger occipital P84 and occipital and temporal N192 components than match stimuli, indicating the existence of involuntary processing in the visual modality. Moreover, the amplitude of the change-related N 192 was larger at the short stimulus onset asynchrony (SOA) than at the long SOA, suggesting that the visual modality involves a mismatch process similar to that of the auditory modality. The underlying neural representation (i.e., the visual memory trace) seems to develop easier and decay faster than its auditory counterpart.