THE VISUAL-PERCEPTION OF RIGID MOTION FROM CONSTANT FLOW-FIELDS

Four experiments investigated observers' judgments of rigidity for dif ferent types of optical motion. The depicted structural deformations w ere of two types: (1) those with nonparallel image trajectories that a re detectable from the first-order spatiotemporal relations between pa irs of views; and (2) those with parallel image trajectories that can only be detected from higher order relations among three or more views . Patterns were composed of smooth now fields in Experiments 1 and 3, and of wire frame figures in Experiments 2 and 4. For both types of di splay, the nonrigidity detectable from the first-order spatiotemporal structure of the motion sequence was much more salient than the deform ation detectable only from the higher order spatiotemporal structure. These results indicate that observers' judgments of rigidity are based primarily on a two-view analysis, but that some useful information ca n be obtained under appropriate circumstances from higher order spatio temporal relations among three or more views.