PARIETAL P3 RESPONSE AS AN INDICATOR OF STIMULUS CATEGORIZATION - INCREASED P3 AMPLITUDE TO CATEGORICALLY DEVIANT TARGET AND NONTARGET STIMULI

Two experiments were performed in which we compared the effects of selected non‐deviant versus categorically deviant stimuli on parietal P3 under a variety of conditions in which one, both, or neither stimulus was a target of an experimental task. Subjects were repeatedly presented with series of 8 numeric stimuli and 1 alphabetic (Deviant) stimulus. P3 amplitudes to target and nontarget Deviant stimuli were consistently and significantly larger than to other, non‐deviant targets and nontargets, respectively. Nontarget Deviant stimuli evoked P3 amplitudes comparable to those evoked by low‐probability non‐deviant targets. The observed differences indicate that P3 amplitude is a sensitive indicator of perceived category differences, and that the effect of category deviance on parietal P3 amplitude is independent of task response classification (target or nontarget) and of response probability. Copyright © 1990, Wiley Blackwell. All rights reserved