Abstract
The perception of unambiguous scaled depth from motion parallax relies on both retinal image motion and an extra-retinal pursuit eye movement signal. The motion/pursuit ratio represents a dynamic geometric model linking these two proximal cues to the ratio of depth to viewing distance. An important step in understanding the visual mechanisms serving the perception of depth from motion parallax is to determine the relationship between these stimulus parameters and empirically determined perceived depth magnitude. Observers compared perceived depth magnitude of dynamic motion parallax stimuli to static binocular disparity comparison stimuli at three different viewing distances, in both head-moving and head-stationary conditions. A stereo-viewing system provided ocular separation for stereo stimuli and monocular viewing of parallax stimuli. For each motion parallax stimulus, a point of subjective equality (PSE) was estimated for the amount of binocular disparity that generates the equivalent magnitude of perceived depth from motion parallax. Similar to previous results, perceived depth from motion parallax had significant foreshortening. Head-moving conditions produced even greater foreshortening due to the differences in the compensatory eye movement signal. An empirical version of the motion/pursuit law, termed the empirical motion/pursuit ratio, which models perceived depth magnitude from these stimulus parameters, is proposed.
Highlights
The visual perception of depth is an important part of successful navigation and obstacle avoidance
The goal of the current study is to: (1) determine how well the motion/pursuit ratio (M/PR) predicts the perception of relative depth from motion parallax in psychophysical observers, and (2) determine whether non-linear transducers applied to the retinal motion signal and to the pursuit signal can produce an “empirical” M/PR model that accounts for the perception of depth magnitude from motion parallax
This point of subjective equality (PSE) gives the binocular disparity of the variable stereo stimulus at one depth that appears to match the magnitude of depth from the fixed binocular disparity of the stereo stimulus viewed at the other distance
Summary
The visual perception of depth is an important part of successful navigation and obstacle avoidance. While the visual system ensures that this fixated object remains stationary on the observer’s retina during the translation, presumably to maintain acuity for the visual information available at this location (Miles, 1998), the retinal image of objects nearer and farther than the fixation point move in opposite directions on the observer’s retina. This combination of retinal motion and eye pursuit was noted as far back as the 1925 edition of von Helmholtz This combination of retinal motion and eye pursuit was noted as far back as the 1925 edition of von Helmholtz (1910/1925/1962, Vol III, p. 371) where the passage concludes, “. . . the probability is that both of them generally contribute to (forming estimates of distance) in some way, it would be hard to say exactly how.” We understand geometrically how the ratio of these rates determines relative depth and experimentally why the motion/pursuit ratio is a key quantity
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