The neural basis of categorical face perception: graded representations of face gender in fusiform and orbitofrontal cortices.

Face gender, like many other things, is perceived categorically: Subjective perceptions are distorted toward the categories, male or female, and the objective gradiency inherent across faces is partially lost. The neural basis of such categorical face perception remains virtually unknown. Participants passively viewed faces whose sexually dimorphic content was morphed monotonically from male to female while neural activity was measured using functional magnetic resonance imaging. Subjective perceptions revealed strong nonlinearity despite monotonic linear changes in face gender, consistent with categorical perception. Neuroimaging results indicated that the lateral fusiform gyrus, bilaterally, and the fusiform face area linearly encoded graded parameters of objective face gender, but these regions correlated substantially less with subjective perceptions (which were nonlinear and affected by categorical perception effects). Such subjective perceptions, however, were represented in the orbitofrontal cortex, but this region correlated substantially less with objective parameters. The attention-independent graded representations of face gender in fusiform and orbitofrontal cortices reveal how objective face parameters are encoded and transformed into subjective categorically warped perceptions in the human brain.