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Mark Nawrot, Lindsey Joyce, Keith Stroyan; Does the motion/pursuit law accurately characterize the perception of depth from motion parallax?. Journal of Vision 2009;9(8):638. doi: 10.1167/9.8.638.
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© ARVO (1962-2015); The Authors (2016-present)
Perception of unambiguous (Nawrot, 2003, Vision Research; Naji & Freeman, 2004, Vision Research) scaled (Nawrot, 2003, Journal of Vision) depth from motion parallax relies on an extra-retinal signal (Nadler et al, 2008, Nature) derived from the pursuit eye movement system (Nawrot & Joyce, 2006, Vision Research). Underlying our experiments is a mathematical motion/pursuit law (Stroyan, 2008, VSS Abst. 23.304) that uses the ratio of retinal image motion and pursuit eye movement to exactly determine the relative depth of an object to the point of fixation. Unlike prior work starting with Nakayama and Loomis (1974, Perception), the motion/pursuit law does not rely on observer speed as a visual input, but does use an extra-retinal pursuit signal. If the motion/pursuit law accurately describes the visual system's function, then changes in perceived depth from motion parallax should be best explained by change in the motion/pursuit ratio, rather than changes in either retinal image motion or pursuit eye movement. Observers were presented two random-dot motion parallax stimuli that could differ in retinal image motion (0.42, 0.625, 0.833, 1.25, or 2.5 deg/sec), pursuit speed (5, 7.5, or 10 deg/sec), and motion/pursuit ratio (0.25, 0.167, 0.125, or 0.083). In each trial the motion parallax stimulus window translated across the monitor, in either direction alternately, changing between the two stimuli at mid-screen. Observers performed a 3AFC task by indicating which of the two stimuli had greater depth magnitude (left, right, or same). Pursuit was monitored with an eye tracker. Multiple regression indicates that one independent variable, change in motion/pursuit ratio, best explains change in perceived depth. While a change in retinal image motion or in pursuit may produce a change in perceived depth, it is due to change in the motion/pursuit ratio. If motion and pursuit change but their ratio remains constant, there is no change in perceived depth.
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