Does face recognition rely on encoding of 3-D surface? Examining the role of shape-from-shading and shape-from-stereo.

It is now well known that processing of shading information in face recognition is susceptible to bottom lighting and contrast reversal, an effect that may be due to a disruption of 3-D shape processing. The question then is whether the disruption can be rectified by other sources of 3-D information, such as shape-from-stereo. We examined this issue by comparing identification performance either with or without stereo information using top-lit and bottom-lit face stimuli in both photographic positive and negative conditions. The results show that none of the shading effects was reduced by the presence of stereo information. This finding supports the notion that shape-from-shading overrides shape-from-stereo in face perception. Although shape-from-stereo did produce some signs of facilitation for face identification, this effect was negligible. Together, our results support the view that 3-D shape processing plays only a minor role in face recognition. Our data are best accounted for by a weighted function of 2-D processing of shading pattern and 3-D processing of shapes, with a much greater weight assigned to 2-D pattern processing.