Systematic distortion of perceived three-dimensional structure from motion and binocular stereopsis.

The geometric relation between physical and perceived space as specified by binocular stereopsis and structure from motion was investigated. Four experimental tasks were used, each of which required a different aspect of three-dimensional (3-D) structure to be performed accurately. To examine whether the transformation between physical and perceptual space preserved the 3-D structural properties required to perform each of our tasks, the constancy of judged shape over changes in a depicted object's viewing distance or orientation was examined. Our results reveal that observers' judgments of 3-D shape from binocular stereopsis and motion contained systematic distortions: Perceived 3-D shape from motion was not invariant over orientation change and perceived 3-D structure from stereo, and motion and stereo in combination was not invariant over changes in viewing distance.