Abstract

Isometric projections of three-dimensional, rigidly rotating polyhedra appear to deform under certain circumstances (Green, 1961, JEP). Relative to those that appear to be rigid, rigidly rotating polyhedra that appear to deform are more difficult to discriminate from ones that actually deform during rotation (Sparrow and Stine, 1990, ARVO). When a rigidly rotating polyhedron appears to deform, the introduction of retinal disparity can result in the perception of rigidity (Sparrow and Stine, 1987a, ARVO). We used polyhedra that were configured either to appear nonrigid or to appear rigid while rigidly rotating (see Sparrow and Stine, 1987b, 1988, OSA). These two classes of stimuli were then presented, one at a time, rotating rigidly (noise trials) or rotating with real deformations (signal + noise trials). Sensitivity to real deformations was less for polyhedra that were more likely to appear to deform than for those that were more likely to appear rigid (replicating Sparrow and Stine, 1990). Adding disparity to a stereo pair of polyhedra that appear to deform can increase sensitivity to real deformations. However, one stereo-blind subject showed no increase in sensitivity with disparity. Disparity allows the subject to see the rigidity of the polyhedron and then discriminate deforming from non-deforming stimuli.

© 1992 Optical Society of America