Moving Cast Shadows and the Perception of Relative Depth

16 June 1994 12:32 pm We describe a number of visual illusions of motion in depth in which the motion of an object's cast shadow determines the perceived 3D motion of the object. The illusory percepts are phenomenally very strong. We analyze the information which cast shadow motion provides for the inference of 3D object motion and experimentally measure human observers' use of this information. The experimental results show that cast shadow information overrides a number of other strong perceptual constraints, including viewers' assumptions of constant object size and a general viewpoint. Moreover, they support the hypothesis that the human visual system incorporates a stationary light source constraint in the perceptual processing of shadow motion. The system imposes the constraint even when image information suggests a moving light source. Moving Cast Shadows and the Perception of Relative Depth