Apparent depth with retinal image motion of expansion and contraction yoked to head movement

The two main questions addressed in this study were (a) what effect does yo king the relative expansion and contraction (EC) of retinal images to forwa rd and backward head movements have on the resultant magnitude and stabilit y of perceived depth, and (b) how does this relative EC image motion intera ct with the depth cues of motion parallax? Relative EC image motion was pro duced by moving a small CCD camera toward and away from the stimulus, two r andom-dot surfaces separated in depth, in synchrony with the observers' for ward and backward head movements. Observers viewed the stimuli monocularly, on a helmet-mounted display, while moving their heads at various velocitie s, including zero velocity. The results showed that (a) the magnitude of pe rceived depth was smaller with smaller head velocities (<10 cm s(-1)), incl uding the zero-head-velocity condition, than with a larger velocity (10 cm s(-1)), and (b) perceived depth, when motion parallax and the EC image moti on cues were simultaneously presented, is equal to the greater of the two p ossible perceived depths produced from either of these two cues alone. The results suggested the role of nonvisual information of self-motion on perce iving depth.