Positive difference in ERPs reflects independent processing of visual changes

To elucidate the nature of the processing of visual stimulus changes, ERPs were recorded while 12 participants performed an S1-S2 matching task with multifeature stimuli. Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either the same as S1, different from S1 only in color, different only in shape, or different in both color and shape. The four trial types were presented in random order with equal probability, and participants responded to one of these types in separate blocks. Relative to the no-change stimuli, the change stimuli elicited posterior positivity with different topography according to changing features ranging from 100 to 180 ms in all tasks. The amplitude and topography of the positivity in response to the both changes were the respective sums of those to changes in the corresponding single features. These results suggest that a feature-specific change detection system exists in the human visual system.