This research applies a perceptual geometry based on the factors of perceived direction and perceived distance to a number of dependent perceptions including those of size, shape, orientation, and especially of motion, as experienced for either stationary stimuli and a moving observer or moving stimuli and a stationary observer. Although, under many circumstances, perceived direction can be assumed at least to approximate physical direction, perceived distance can be seriously in error. It is proposed that these errors have important consequence for the dependent perceptions as manifested in such phenomena as the illusory motion or orientation of a Necker cube, a trapezoidal window, an inverted face mask, and the folded card demonstration of Mach. It is additionally proposed that this approach can be useful in the manipulation and analysis of anorthoscopic perception and in the similarities and differences found in depth cues of relative motion parallax, relative size, and binocular disparity, especially as these concern the inverse square law. Also to be investigated are the perceptions occurring from optical expansion under conditions of sagittal motion of either the stimulus or the observer. The special contribution of motion to spatial perception will be investigated by comparing illusory motion and orientation under static and dynamic conditions of observation. Predictions from the theory used in this approach will be compared experimentally to predictions from other suggested explanations of the same phenomena involving inferential and expectation or compensation processes.
