The kinetic depth effect.

Abstract
A report of 10 experiments dealing with the perception of three dimensional form. It is found that when a 3 dimensional form, solid or wire edged, is turned behind a translucent screen, the Ss perceive the shadow as a 3 dimensional object quite similar to the physical object. A necessary condition is that the shadow must display contours or lines which change their length and their direction simultaneously. The authors believe this effect to operate widely under ordinary circumstances. (PsycINFO Database Record (c) 2006 APA, all rights reserved)