The influence of stimulus deviance on electrophysiologic and behavioral responses to novel events

This study investigated the role of stimulus deviance in determining electr ophysiologic and behavioral responses to "novelty." Stimulus deviance was d efined in terms of differences either from the immediately preceding contex t or from long-term experience. Subjects participated in a visual event-rel ated potential (ERP) experiment, in which they controlled the duration of s timulus viewing with a button press, which Served as a measure of explorato ry behavior. Each of the three experimental conditions included a frequent repetitive background stimulus and infrequent stimuli that deviated from th e background stimulus. In one condition, both background and deviant stimul i were simple, easily recognizable geometric figures. In another condition, both background and deviant stimuli were unusual/unfamiliar figures, and i n a third condition, the background stimulus was a highly unusual figure, a nd the deviant stimuli were simple, geometric shapes. Deviant stimuli elici ted larger N2-P3 amplitudes and longer viewing durations than the repetitiv e background stimulus, even when the deviant stimuli were simple, familiar shapes and the background stimulus was a highly unusual figure. Compared to simple, familiar deviant stimuli, unusual deviant stimuli elicited larger N2-P3 amplitudes and longer viewing times. Within subjects, the deviant sti muli that evoked the largest N2-P3 responses also elicited the longest view ing durations. We conclude that deviance from both immediate context and lo ng-term prior experience contribute to the response to novelty, with the co mbination generating the largest N2-P3 amplitude and the most sustained att ention. The amplitude of the N2-P3 mag reflect how much "uncertainty" is ev oked by a novel visual stimulus and signal the need for further exploration and cognitive processing.