Figure 3.

Abrogated motion parallax. (A) Illustration of motion parallax. When the head is moved (i), an object in the foreground moves in the opposite direction with respect to the background (ii). If the foreground object happens to be a cube, the proximal faces move a greater distance to the left than the distal faces, as illustrated. (The conventions are the same as in Figs. 1 and 2). Although the sequence of retinal image changes is geometrically indistinguishable from object rotation, prior experience evidently has taught us to ignore this alternative possibility in favor of perceiving depth through motion parallax (iii). (B) When the retinal image generated by the transparent cube is interpreted to be in its illusory (bottom-up) orientation (i), the familiar response to head movement (i.e., motion parallax) no longer occurs. The proximal and distal faces of the transparent figure now change with respect to each other in a manner opposite that which occurs when the cube is perceived as it actually is (ii). In this circumstance, the cube is seen to be rotating in the direction of the head movement (iii).