Electrophysiological evidence of implicit and explicit categorization processes

Event-related brain potentials (ERPs), which provide on-line measures of ca tegorization processes, were used to assess the implicit and explicit categ orization of stimuli along evaluative (positive and negative) and nonevalua tive (people and no-people) dimensions. Participants were exposed to stimul i that simultaneously varied along both dimensions, but were explicitly ins tructed to categorize along only one of them. Consistent with prior researc h, the late positive potential (LPP) of the ERP was sensitive to participan ts' explicit categorization task. However, the LPP also revealed implicit c ategorization along the non-task-relevant dimension. Additionally, there wa s evidence of an implicit negativity bias in which negative stimuli spontan eously received greater processing than positive stimuli and a people/no-pe ople analog in which stimuli containing people received greater processing than stimuli without people. Results suggest the operation of adaptively be neficial implicit categorization processes, triggered by significant proxim al stimuli, serving broad, cross-situational goals. (C) 2000 Academic Press .