The effects of parts, wholes, and familiarity on face-selective responses in MEG

Abstract

Although face perception is commonly thought to rely on holistic, rather than part-based, processing, there is some evidence for part-based representations in the face processing stream. Previously (VSS 2007), we have probed holistic and part-based processing with faces manipulated in stereoscopic depth to appear either behind or in front of a set of stripes (Nakayama et al., 1989), which we have demonstrated behaviorally are perceived holistically or in terms of their constituent parts, respectively. Using these stimuli in functional magnetic resonance imaging (fMRI), we showed that “face-selective” regions respond equally to face parts and wholes. Within the right fusiform gyrus, we further found an interaction of processing and familiarity, with greater adaptation for the holistic relative to part-based condition for familiar but not unfamiliar faces. Here we extend this work by investigating the time course of these processing and familiarity effects using magnetoencephalography (MEG). We examined “face-selective” (Face [[gt]] House) components in occipitotemporal sensors at early (∼170–200 ms) and later (∼250–450 ms) latency ranges. While both M170 and “M400” components showed significantly larger responses for familiar versus unfamiliar faces, neither exhibited a main effect of holistic versus part-based processing, as indexed by depth. These data affirm the existence of “face-selective” part-based representations, and additionally demonstrate that such representations are present from relatively early stages of face processing. However, the interaction of familiarity and depth only reached significance in the later M400 latency range, with a larger response to the holistic condition for familiar but not unfamiliar faces. Likewise, behavioral recognition performance was significantly correlated with the M400, but not the M170, and only in the holistic condition. Together, these results suggest that, while face parts are represented from the early stages of processing indexed by the M170 response, modulatory effects of familiarity seen with fMRI occur later in the face processing stream.