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Mark Nawrot, Mik Ratzlaff, Zach Leonard, Keith Stroyan; Modeling perceived depth from motion parallax with the motion/pursuit ratio. Journal of Vision 2011;11(11):705. doi: https://doi.org/10.1167/11.11.705.
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© ARVO (1962-2015); The Authors (2016-present)
The perception of depth from motion parallax may be described by a dynamic process that compares the proximal visual cues of retinal image motion (dθ) and pursuit eye movements (dα) to approximate the ratio of relative depth (d) to viewing distance (f) (Nawrot & Stroyan, 2009). This motion/pursuit ratio (M/PR), d/f ∼ dθ/ dα, represents a quantitative model for motion parallax and makes specific predictions of relative depth judgments (vis. d ∼ dθ/dα * f). The goal of the current study is to determine how the M/PR characterizes perceived depth magnitude from motion parallax. In particular, the M/PR predicts foreshortening of depth from motion parallax, with magnitude of the foreshortening increasing with increasing M/PR. Observers performed comparisons of perceived depth magnitude between motion parallax and binocular stereopsis stimuli. A Z_Screen stereo system provided ocular separation for stereo stimuli and monocular viewing of parallax stimuli. Random_dot parallax stimuli translated laterally generating pursuit (dα) while stimulus dots within the stimulus also shifted laterally (dθ). The stereo stimuli, identical in composition to the parallax stimuli, were stationary. Parallax stimuli had a range of M/PR (0.04–0.24) while stereo stimuli had a range of disparities (1.2–11 min). For each M/PR, a point of subjective equality was estimated from the psychometric function, giving the amount of binocular disparity that generates the equivalent magnitude of perceived depth. Similar to previous results, perceived depth from motion parallax had significant foreshortening, even more than predicted by the M/PR. However, as predicted, foreshortening increased with larger values of M/PR. The M/PR provides a reasonable explanation for perceived depth from motion parallax. One explanation for the additional depth foreshortening is the difference in pursuit signals generated by a translating observer fixating a stationary point, and a stationary observer pursuing a translating point.
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