Abstract
To recover unambiguous depth from motion parallax, the visual system uses an extra-retinal pursuit eye movement signal. As a simple quantitative model of this process, we propose that relative depth (d) is determined from: fixation distance (f), retinal image motion (dθ/dt or dθ), and an extra-retinal pursuit eye movement signal (dα/dt or dα) using what we term the motion/pursuit ratio: d/f = dθ/dα. The motion/pursuit ratio explains changes in perceived depth better than changes in dθ and dα alone. Moreover, investigation of the required integration time for dθ and dα suggests that depth from motion parallax is a relatively quick process (≍75 msec), limited by the interval needed to generate the internal pursuit signal.