The perception and recognition of natural object shape from deforming and static shadows

In this study of the informativeness of shadows for the perception of objec t shape, observers viewed shadows cast by a set of natural solid objects an d were required to discriminate between them. In some conditions the object s underwent rotation in depth while in other conditions they remained stati onary, thus producing both deforming and static shadows. The orientation of the light source casting the shadows was also varied? leading to further a lterations in the shape of the shadows. When deformations in the shadow bou ndary were present, the observers were able to reliably recognize and discr iminate between the objects, invariant over the shadow distortions produced by movements of the light source. The recognition performance for the stat ic shadows depended critically upon the content of the specific views that were shown. These results support the idea that there are invariant feature s of shadow boundaries that permit the recognition of shape (cf Koenderink, 1984 Perception 13 321-330).