Relative motion parallax and the perception of structure from motion

Empirical findings are reported that delineate properties of the process underlying the perception of structure from motion (SfM). First, it is shown that the usual rotating kinetic depth displays generally involve at least two sources of information: relative motion parallax and changes in the projected envelope of the rotating object. Then, evidence is presented that even when variations in projected envelope are minimized, altering the 3-D motion of an object can greatly affect its perceived shape in ways that hint at properties of the underlying process. It is also shown that circular patterns of relative motion parallax not associated with a rigidly moving object can elicit the perception of depth variation, and that added image rotations which by themselves do not elicit apparent depth variation can nevertheless influence the apparent shape of such circular patterns