THE VALENCE STRENGTH OF NEGATIVE STIMULI MODULATES VISUAL NOVELTY PROCESSING: ELECTROPHYSIOLOGICAL EVIDENCE FROM AN EVENT-RELATED POTENTIAL STUDY

In natural settings, the occurrence of unpredictable infrequent events is often associated with emotional reactions in the brain. Previous research suggested a special sensitivity of the brain to valence differences in emotionally negative stimuli. Thus, the present study hypothesizes that valence changes in infrequent negative stimuli would have differential effects on visual novelty processing. Event-related potentials (ERPs) were recorded for highly negative (HN), moderately negative (MN) and Neutral infrequent stimuli, and for the frequent standard stimulus while subjects performed a frequent/infrequent categorization task, irrespective of the emotional valence of the infrequent stimuli. The infrequent-frequent difference waves, which index visual novelty processing, displayed larger N2 amplitudes during HN condition than during MN condition which, in turn, elicited greater N2 amplitude than the Neutral condition. Similarly, in the infrequent-frequent difference waves, the frontocentral P3a and parietal LPC (late positive complex) elicited by the HN condition were more negative than those by MN stimuli, which elicited more negative amplitudes than the Neutral condition. This suggests that negative emotions of diverse strength, as induced by negative stimuli of varying valences, are clearly different in their impact on visual novelty processing. Novel stimuli of increased negativity elicited more attentional resources during the early novelty detection, and recruited increased inhibitive and evaluative processing during the later stages of response decision and reaction readiness, relative to novel stimuli of reduced negativity. (C) 2008 IBRO. Published by Elsevier Ltd. All rights reserved.