Abstract

Perceived orientation of axis of rotation and accuracy in discriminating fixed-axis from nordixed-axis rotations were investigated for orthographic projections of three-dimensional rotating objects. The principal findings were (a) the slant of the axis of rotation was systematically misperceived; (b) in both two-view and multiview displays, the perceived slant of the axis of rotation was well-predicted by the ratio between the deformation (a property of the first-order optic flow) and the component parallel to the image plane of the global velocity vector; (c) if this ratio was kept constant in each frame transition of the stimulus sequence (or it was varied), then the stimuli tended to be judged as fixed-axis rotations (or as nonfixed-axis rotations), regardless of whether they simulated a fixed-axis rotation or not; and (d) the tilt of the axis of rotation was perceived in two-view displays with a very small error. A changing two-dimensional (2-D) projection of an object's motion gives rise to a compelling impression of a volumetric shape moving in three-dimensional (3-D) space. This phenomenon (called the kinetic depth effect [KDE] after Wallach & O'Cormell, 1953) represents an essential

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