The Fusiform Gyrus Processes Faces Relative to an Overall Face Average and a Person Average

Abstract

We are highly accurate at recognizing familiar faces even with large variation in visual presentation due to pose, lighting, hairstyle, etc. The neural basis of such within-person face variation has been largely unexplored. Building on prior behavioral work, we hypothesized that learning a persons average face helps link the different instances of that persons face into a coherent identity within face-selective regions within ventral occipitotemporal cortex (VOTC). To test this hypothesis, we measured brain activity using fMRI for eight well-known celebrities with 18 naturalistic photos per identity. Each photo was mapped into a face-space using a neural network where the Euclidean distance between photos corresponded with face similarity. We confirmed in a behavioral study that photos closer to a persons average face in a face-space were judged to look more like that person. fMRI results revealed hemispheric differences in identity processing. The right fusiform face area (FFA) encoded face-likeness with brain signal increasing the closer a photo was to the average of all faces. This suggests that the right FFA pattern matches to an average face template. In contrast, the left FFA and left anterior fusiform gyrus (aFus) encoded person-likeness. The brain signal increased the further a photo was from the persons average face weighted by the features most relevant for face identification. This suggests that the left FFA and aFUS processes an identity error signal. Our results encourage a new consideration of the left fusiform in face processing, specifically for within-person processing of face identity.