Event-related brain potentials distinguish processing stages involved in face perception and recognition.

OBJECTIVES: An event-related brain potential (ERP) study investigated how different processing stages involved in face identification are reflected by ERP modulations, and how stimulus repetitions and attentional set influence such effects.METHODS: ERPs were recorded in response to photographs of familiar faces, unfamiliar faces, and houses. In Part I, participants had to detect infrequently presented targets (hands), in Part II, attention was either directed towards or away from the pictorial stimuli.RESULTS: The face-specific N170 component elicited maximally at lateral temporal electrodes was not affected by face familiarity. When compared with unfamiliar faces, familiar faces elicited an enhanced negativity between 300 and 500 ms ('N400f') which was followed by an enhanced positivity beyond 500 ms post-stimulus ('P600f'). In contrast to the 'classical' N400, these effects were parietocentrally distributed. They were attenuated, but still reliable, for repeated presentations of familiar faces. When attention was directed to another demanding task, no 'N400f' was elicited, but the 'P600f' effect remained to be present.CONCLUSIONS: While the N170 reflects the pre-categorical structural encoding of faces, the 'N400f' and 'P600f' are likely to indicate subsequent processes involved in face recognition. Impaired structural encoding can result in the disruption of face identification. This is illustrated by a neuropsychological case study, demonstrating the absence of the N170 and later ERP indicators of face recognition in a prosopagnosic patient.