Abstract

A fundamental problem in the study of spatial perception concerns whether and how vision might acquire information about the metric structure of surfaces inthree-dimensionaLspacefrom motion and from stereopsis. Theoretical analyses have indicated that stereoscopic perceptions of metric relations in depth require additional information about egocentric viewing distance; and recent experiments by James Todd and his colleagues have indicated that vision acquires only afline but notmetric structure from motion—that is, spatial relations ambiguouswith regard to scale in depth. The purpose of the present study was to determine whether the metric shape ofplanar stereoscopic forms might be perceived from congruence underplanar rotation. In Experiment 1, observers discriminated between similar planar shapes (ellipses) rotating in a plane with varying slant from the frontal-parallel plane. Experimental conditions varied the presence versus absence of binocular disparities, magnification of the disparity scale, and moving versus stationary patterns. Shape discriminations were accurate in all conditions withmovingpatterns and were near chance in conditions with stationary patterns; neither-the- presence nor the magnification of binocular disparities had any reliable effect. In Experiment 2, accuracy decreased as the range of rotation decreased from 800 to 100. In Experiment 3, small deviations from planarity of the motion

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