Shape, orientation, and apparent rotational motion.

TLDR

The study examined how apparent rotational motion is perceived in polygonal shapes with varying degrees of rotational symmetry up to 180 degrees. Observers adjusted the alternation rate between two computer‑displayed orientations of each polygon to locate the point at which perceived rigid rotation breaks down. Asymmetric polygons required longer stimulus‑onset asynchronies for apparent rigid rotation that increased linearly with orientational disparity, whereas nearly symmetric polygons showed a marked rise in critical time near 180 degrees due to a shorter nonrigid rotation, revealing competing mental tendencies to preserve rigid structure and to follow the shortest transformational path.

Abstract

Apparent rotational motion was investigated in polygonal shapes ranging in rotational symmetry from random to self-identical under 180 degrees rotation. Observers adjusted the rate of alternation between two computer-displayed orientations of any given polygon to determine the point of breakdown of perceived rigid rotation between those two orientations. For asymmetric polygons, the minimum stimulus-onset asynchrony yielding apparent rigid rotation increased approximately linearly with orientational disparity, as anticipated on the basis of the extension of Korte's third law to rotational motion by Shepard and Judd. For nearly symmetric polygons, however, the critical time increased markedly as the disparities approached 180 degrees, owing to the availability of a shorter, nonrigid rotation in the opposite direction. The results demonstrate the existence of competing mental tendencies to preserve the rigid structure of an object and to traverse a minimum transformational path.