Shape constancy is referred to as the tendency for the perceived shape of an object to
remain unchanged even under changed viewing and illumination conditions. We investigated, in
two experiments, whether shape constancy would hold for images of 3-D solid objects defined
by shading only, whose renderings differed in terms of surface material type (bi-directional reflectance distribution functions), light field, light direction, shape, and specularity. Observers were
presented with the image of a sphere or an ellipsoid and required to set perceived orientation
and cross-section profile on designated points of the image. Results showed that shape judgments
varied with all the aforementioned variables except specularity. Shape estimates were more precise with specular than asperity scattering surfaces, collimated than hemispherical diffuse lighting
conditions, lower than higher elevations, spherical than ellipsoidal shapes, but not different
between surfaces having differing specularity. These results suggest that shape judgments are
made largely on the basis of the overall intensity distribution of shading, and that the portions of intensity distribution that are due to nonstructural variables such as surface material type or
light field are not excluded in the process of shape estimation, as if being due to structural components. It is concluded that little constancy is expected in the perception of shape from shading
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