Abstract

It has been known since the 1970s that there are neurons in the monkey visual system that are sensitive
to faces. These face cells have been studied in most detail in the anterior inferior temporal (IT)
cortex and the upper bank of the superior temporal sulcus (STS), but they also occur in other areas such
as the amygdala and the inferior convexity of the prefrontal cortex (Figure 1).
Characteristically, the optimal stimuli of face cells cannot be deconstructed into simpler component
shapes (Wang et al., 1996). In general, these cells show virtually no response to any other stimulus
tested (such as textures, gratings, bars, and the edges of various colors), but respond strongly to a
variety of faces, including real ones, plastic models, and video display unit images of human and
monkey faces. The responses of many face cells are invariant to size and position; the cell’s response
is maintained when there is a change in the size of the face, or if the position of the face
within the cell’s receptive field is altered. Face cells do not respond well to images of faces that have
had the components rearranged, even though all the components are still present and the outline is
unchanged (e.g., Perrett et al., 1992). Face cells are even sensitive to the relative position of features
within the face; particularly important is inter-eye distance, distance from eyes to mouth, and the
amount and style of hair on the forehead (e.g., Young and Yamane, 1992)