N400 and LPP in spontaneous trait inferences.

Past research on spontaneous trait inferences using event related potentials (ERPs) has consistently reported increased late positive potential (LPP) amplitudes following social expectancy violations, but no N400 modulation. In the present study, participants read scenarios describing behaviors of unknown actors. They entailed descriptions of several positive trait implying behaviors, followed by a single final sentence describing behavior that was either consistent or inconsistent with the previously implied trait. As in previous studies, we found significantly increased LPP amplitudes following inconsistent behaviors at multiple frontal sites. Unlike in previous research, we also found increased N400 amplitudes at several centro-parietal sites. The divergence of these results is explained from minor differences in the stimulus presentation procedure and possible overlap of ERP components of opposite polarity. Temporal principal component analysis (PCA) confirmed the separate influence of concurrent LPP and N400 ERP modulations, and the source of the largest factors was located using sLORETA. It is suggested that the increased N400 in response to trait inconsistencies reflects difficulties in understanding unanticipated behavior, while the LPP effect might reflect evaluative incongruence.