Electrophysiological studies of human face perception. III: Effects of top-down processing on face-specific potentials.

This is the last in a series of papers dealing with intracranial event-related potential (ERP) correlates of face perception. Here we describe the results of manipulations that may exert top-down influences on face recognition and face-specific ERPs, and the effects of cortical stimulation at face-specific sites. Ventral face-specific N200 was not evoked by affective stimuli; showed little or no habituation; was not affected by the familiarity or unfamiliarity of faces; showed no semantic priming; and was not affected by face-name learning or identification. P290 and N700 were affected by semantic priming and by face-name learning and identification. The early fraction of N700 and face-specific P350 exhibited significant habituation. About half of the AP350 sites exhibited semantic priming, whereas the VP350 and LP350 sites did not. Cortical stimulation evoked a transient inability to name familiar faces or evoked face-related hallucinations at two-thirds of face-specific N200 sites. These results are discussed in relation to human behavioral studies and monkey single-cell recordings. Discussion of results of all three papers concludes that: face-specific N200 reflects the operation of a module specialized for the perception of human faces; ventral and lateral occipitotemporal cortex are composed of a complex mosaic of functionally discrete patches of cortex of variable number, size and location; in ventral cortex there is a posterior-to-anterior trend in the location of patches in the order letter-strings, form, hands, objects, faces and face parts; P290 and N700 at face-specific N200 sites, and face-specific P350, are subject to top-down influences.