DISCRIMINATING CONSTANT FROM VARIABLE ANGULAR VELOCITIES IN STRUCTURE-FROM-MOTION

We investigated accuracy in discriminating between constant and variab le angular velocities for orthographic projections of three-dimensiona l rotating objects. The reported judgments of ''constant'' or ''variab le'' angular velocity were only slightly influenced by the projected a ngular velocities, but they were greatly affected by the variations of the deformation, a first-order component of the optic flow. When view ing either a rotating ellipsoidal volume or a planar surface that acce lerated and decelerated over the course of rotation, observers' tenden cies to report a variable angular velocity were increased when the tem poral phase of the acceleration pattern increased the range of variati on of the median deformation; the tendencies were decreased when the s ame acceleration pattern was used to decrease the range of variation o f the median deformation. These results provide evidence contrary to t he hypothesis that the visual system performs a mathematically correct analysis of the optic flow.