ABSTRACT
Living in the physical world requires the observer to perceive the structure of objects and their motion as well as his own motion in three dimensions. For simplicity, most studies on motion perception have been restrained to one or two dimensions. Psychophysical and neurophysiological results on object-motion perception by mammals have been essentially confined to motion in a frontal plane or to in-depth motion. Although the physical motion of a point can be decomposed into its frontal and in-depth components, its perception by the visual system may not follow the same rule, for these two components have not been proven to be perceptually independent.
