Abstract: The human visual perception of motion in depth is based on thespecific sensitivities to two-dimensional relative motion on the fron-tal plane. Several psychophysical experiments were carried out todisclose the mathematical and physiological aspects of these sensitivi-ties. It was concluded that the human visual system contains neu-rons tuned to relative motion on the frontal plane, which formedthe mechanisms of recovering motion in depth. The psychophysicaland physiological evidences were shown for the monocular and bino-cular perceptions of motion in depth. The difference between visualperceptions of motion in depth of humans and those of insects werealso discussed.

Key words: motion in depth, relative motion, velocity difference, disparity, neural elements