Face configuration processing in the human brain: the role of symmetry

Abstract

Symmetry is an important cue in face perception. We manipulated symmetry and other configurational variables to study their role in face processing in the human brain. We employed 2 types of symmetry: image symmetry (where one part of the image is defined as the mirrored transform of the other part about an axis) and object symmetry (where the spatial relationships among the image components are interpreted as parts of a symmetric 3-dimensional object). We compared blood oxygenation level dependent responses in healthy human observers for upright front-view faces with responses to different symmetry-controlled images. The cortical areas activated by the face images, relative to Fourier-matched scrambled images, were the fusiform (FFA) and occipital (OFA) face areas, the middle occipital gyri (MOG), and areas around the superior temporal and intraoccipital sulci (IOS). Contrasting faces and their image-symmetric scrambled versions showed a similar activation pattern except in the right OFA, suggesting an involvement in facial symmetry processing. The upright versus inverted faces (with the same image symmetry but unfamiliar object identity) showed robust differential activation in the FFA, OFA, MOG, IOS, and precuneus. The response to frontal-view versus 3/4-view faces (having the same object symmetry but disrupted image symmetry) showed little differential activation in the FFA or the OFA but strong responses in the MOG and IOS, suggesting that face processing in the FFA and the OFA is holistic and viewpoint invariant.