Dissociation of event-related potential repetition effects in judgments of face identity and expression

Event-related potentials (ERPs) were recorded while 12 subjects (mean age 24 years) decided whether sequentially presented pairs of faces were either of the same identity or, in separate blocks of trials, the same expression. ERP repetition effects were observed in the responses to the second stimulus on trials on which either the identity or expression matched. In the case of identity marches this consisted of an early frontal repetition effect in the latency range 200-300 ms followed by a later parietal repetition effect in the latency range 350-550 ms consistent with a modulation of an N4 component. There was no significant modulation of the P3 component (P600 or LPC) in this task which is consistent with the task parameters. Only the later N4 repetition effect was observed in the case of the expression matching task. ERPs in the interval between the first and second stimulus were relatively more negative at the right parietal site, but relatively more negative at both right parietal and temporal sites after the second stimulus. The observed dissociation of ERP effects for identity and expression processing ore discussed both in terms of their relationship to theories of semantic memory organization and long term and working memory function.