Conflicting motion perspective simulating simultaneous clockwise and counterclockwise rotation in depth

The interplay between stereopsis and structure from motion

In a series of psychophysical experiments, an adaptation paradigm was employed to study the influence of stereopsis on perception of rotation in an ambiguous kinetic depth (KD) display. Without prior adaptation or stereopsis, a rotating globe undergoes spontaneous reversals in perceived direction of rotation, with successive durations of perceived rotation being random variables. Following 90 sec of viewing a stereoscopic globe undergoing unambiguous rotation, the KD globe appeared to rotate in a direction opposite that experienced during the stereoscopic adaptation period. This adaptation aftereffect was short-lived, and it occurred only when the adaptation and test figures stimulated the same retinal areas, and only when the adaptation and test figures rotated about the same axis. The aftereffect was just as strong when the test and adaptation figures had different shapes, as long as the adaptation figure contained multiple directions of motion imaged at different retinal disparities. Nonstereoscopic adaptation figures had no effect on the perceived direction of rotation of the ambiguous KD figure. These results imply that stereopsis and motion strongly interact in the specification of structure from motion, a result that complements earlier work on this problem.

The effects of spatial and temporal factors on the perception of stroboscopic rotation simulations

In the present two experiments subjects viewed discontinuous, i.e. stroboscopic, simulations of a transparent sphere partially filled with randomly positioned luminous dots and rotating about the y axis in depth. Over a range of stimulus conditions, such simulations elicited coherent sensations of continuous rotation and internal volume of the sphere. By manipulating both spatial and temporal variables in the simulations, it was attempted to define the boundary conditions for which corresponding elements of a simulation are perceptually paired from frame to frame to yield coherent sensations of rotation and depth. The results indicated that the process that matches or pairs corresponding elements in a three-dimensional simulation cannot be identified with the process that matches corresponding elements in similar two-dimensional displays. Furthermore, temporal factors influenced the perception of these simulations more than did spatial factors, and rotation-judgment accuracy and perceived depth were different functions of temporal frequency. Over a range of temporal frequencies, such three-dimensional simulations are apparently processes in a manner similar to that in which objects undergoing real motion are processed.