A neglected problem: kinetic size constancy.

Size constancy in three-dimensional motion, "kinetic size constancy", was investigated by measuring both perceived size and perceived distance under monocular and binocular viewing conditions. It was found that forward-motion facilitated a tendency to see an object with an approximately constant size and made it possible to perceive veridically the distance to the object (distance constancy). The size-distance invariance hypothesis, expressed in the form S'/D'=K theta n, was found to hold in the present experimental situation. In contrast to static size constancy, with kinetic size constancy there is no requirement for separate depth cues if a focal stimulus changes along its vertical and horizontal dimensions and this results in the perception of a shape.