In four experiments, a scalar judgment of perceived depth was used to examinethe spatial and temporal characteristics of the perceptual buildup of three-dimensional (3-D) structure from optical motion as a function of the depth in the simulated object, the speed of motion, the number of elements defining the object, the smoothness of the optic flow field, and the type of motion. In most of the experiments, the objects were polar projections of simulatedhalf-ellipsoids undergoing a curvilinear translation about the screen center. It was foundthat-thebuiklupof3-D structure was: (1) jointly dependent on the speed at which an object moved and on the range through which the object moved; (2) more rapid for deep simulated objects than for shallow objects; (3) unaffected by the number of points defining the object, including the maximum apparent depth within each simulated object-depth condition; (4) not disrupted by nonsmooth optic flow fields; and (5) more rapid for rotating objects than for curvilinearly translating objects. The human visual system has the remarkable ability to recover three-dimensional (3-D) shape when it is presented with a rapid succession of 2-D views of a moving object. Even when each view by itself contains no information about three-dimensionality, depth can still be perceived. In their now classic study, Wallach and O’Connell (1953) named this phenomenon the kinetic depth effect (KDE). Recent investigators have called the phenomenon the recovery of structurefrom motion (SFM) (e.g., Todd, 1984; Ullman, 1979, 1984). When viewing a KDE display, one often has the impression that the time course for the structural buildup is quite short. Wallach and O’Connell (1953) took note of this factwhen they observed that “turning wire-figures were seen threedimensionally immediately upon presentation” (p. 208). Surprisingly, until recent years, there was very little data about the temporal characteristics of the process involved in the recovery of SFM (see Hildreth
