One plus one is less than two: visual features elicit non-additive mismatch-related brain activity.

In a passive oddball task (performing in a video game), participants were presented with sequences of either standard stimuli or patterns containing deviant orientation, deviant spatial frequency or both deviant orientation and spatial frequency. Orientation deviants presented to the lower half of the visual field elicited a posterior negative component with a peak latency of 130 ms. Spatial frequency deviants elicited a similarly negative component that was later followed by another negative component. Activity elicited by the double-deviant stimulus was identical to activity elicited by the orientation deviant alone. The subtraction difference of the peak latency and scalp distribution of the deviant minus the standard difference potentials were unequal to those of the exogenous event-related potential (ERP) components and were therefore considered visual mismatch negativities (vMMNs). The non-additivity of the feature-related responses is interpreted as sensitivity of the implicit change-detection system to deviant events rather than an exclusive sensitivity to individual features. Deviant stimuli presented to the upper half of the field elicited responses with positive polarity, but this activity was less pronounced than the vMMN. Polarity reversal of the response to upper half-field stimulation suggests that the origin of the activity lies in retinotopic areas. Because of the emergence of a mismatch component with positive polarity, we propose that the term visual mismatch negativity (vMMN) be replaced with the more general term visual mismatch response (vMMR).