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Mark Nawrot, Keith Stroyan; Integration time for the mechanisms serving the perception of depth from motion parallax. Journal of Vision 2010;10(7):50. doi: 10.1167/10.7.50.
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© ARVO (1962-2015); The Authors (2016-present)
Our recent quantitative model for the perception of depth from motion parallax (MP), based on the dynamic geometry of MP, proposes that relative object depth (d) can be determined from fixation distance (f), retinal image motion (dθ/dt), and pursuit eye movement (dα/dt) with formula: d/f = dθ/dα (Nawrot & Stroyan, 2009). Given the model's dynamics, it is important to know the integration time required by the visual system to recover dα and dθ, and then estimate d. If the perception of depth from motion is sluggish, and needs to “build-up” over a period of observation, then the potential accuracy of the depth estimate suffers as the observer moves during the viewing period. A depth-phase discrimination task was used to determine the time necessary to perceive depth from MP. Observers remained stationary and viewed a briefly translating (4 deg/s) random-dot MP stimulus on a CRT (120 Hz) at 57 cm. The stimulus was 6.6 deg2, having 4000 2 min2 dots. Fixation on the translating stimulus was monitored with an ASL eye tracker. Stimulus duration was varied within an interleaved staircase procedure for leftward and rightward eye-movements. Depth-discrimination can be performed with presentations as brief as 16.6 msec, with only two stimulus frames providing both retinal image motion and the stimulus window motion for pursuit (mean range = 16.6–33.2 msec). This was found for conditions in which, prior to stimulus presentation, the eye was engaged in ongoing pursuit or the eye was stationary. A large (13 deg2) high-contrast masking stimulus (83 msec) disrupted depth-discrimination for stimulus presentations less than 60-80 msec in both pursuit and stationary conditions. We conclude that neural mechanisms serving depth from MP generate a depth estimate quickly, <90 msec. This interval might be linked to ocular-following response eye-movement latencies. Any additional sluggishness in MP might be due to head movement dynamics.
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