Early computation of shape and reflectance in the visual system.

A compelling sense of three-dimensional shape may be conveyed by the photograph of an object. Cues such as contour, shading, perspective and occlusion, to name a few, contribute to this percept. Psychophysical experiments suggest that certain aspects of three-dimensional shape are computed rapidly and in parallel by the visual system. Here we report that reflectance is also computed rapidly; moreover, it is the apparent reflectance, rather than brightness or perceptual three-dimensional shape, that is the primary basis for discrimination during the early stages of visual processing.