Does motion perspective independently produce the impression of a receding surface?

Motion parallax as a fact of optics has been known for a long time. When an observer moves, the apparent relative motion of two or more stationary objects in the visual field is an indicator or clue to their relative distance. The theory that tridimensional perception depends on the interpretation of bidimensional sensations specifies a list of such clues or cues for depth and distance, and motion parallax is an important item on this list. Helmholtz argued that during locomotion, for instance, the apparent angular velocities of objects in the field of view will be inversely proportional to their real distances away; and consequently safe conclusions can be drawn as to the real distance of the body (5, p. 295). The reason why these sensations of velocity are experienced as distance rather than as velocity is that the process of interpretation or inference has become so habitual as to become unconscious. We learn to see relative motion as relative distance during the course of growing up in the environment. However, this perception is never more than a safe conclusion. As Helmholtz was careful to point out, the cues for depth are not compelling for the impression of depth; they function as such only when experience makes the assumption of a third dimension reasonable. The writer has suggested that this theory is formulated only for objects in space, and that the background of 1 The experiment here reported was carried out by Walter Carel under the general supervision of