Depth from motion parallax scales with eye movement gain.

Recent findings suggest that the slow eye movement system, the optokinetic response (OKR) in particular, provides the extra-retinal signal required for the perception of depth from motion parallax (Nawrot, 2003). Considering that both the perception of depth from motion parallax (Ono, Rivest & Ono, 1986; Rivest, Ono & Saida, 1989) and the eye movements made in response to head translations (Schwarz & Miles 1991; Paige, Telford, Seidmen, & Barnes, 1998) appear to scale with viewing distance, changes in perceived depth from motion parallax were studied as a function of viewing distance. If OKR is used in the perception of depth from motion parallax, a change in the OKR signal, caused by a change in viewing distance, should accompany a change in perceived depth from motion parallax. Over a range of viewing distances, binocular stereopsis was used to index perceived depth from motion parallax. At these viewing distances the gain of the OKR portion of the compensatory eye movement was also determined. The results show that the change in OKR gain is mirrored by the change in perceived depth from motion parallax as viewing distance increases. This suggests that the OKR eye movement signal serves an important function in the perception of depth from motion.