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Jake A Whritner, Thaddeus B Czuba, Lawrence K Cormack, Alexander C Huk; Temporal integration of isolated 3D motion cues. Journal of Vision 2019;19(10):235a. doi: https://doi.org/10.1167/19.10.235a.
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INTRODUCTION. Previously, we have shown that 3D motion is integrated over time by a distinct mechanism that is more sluggish than the integrator for frontoparallel motion (Katz et al., 2015). Here, we enquire whether the two primary binocular cues to 3D motion—changing disparity (CD) and interocular velocity difference (IOVD)—have distinct temporal integration profiles. Given the evidence that the CD and IOVD mechanisms operate at relatively low and high stimulus speeds, respectively, we reasoned that they might have different integration times as well. METHODS. We varied stimulus duration (67-1067 ms) and measured response accuracy during a 3D discrimination task. Observers viewed either an IOVD- or CD-only stimulus moving towards or away in depth and reported direction of motion via key press. For the IOVD-isolating condition, we modified the novel stimulus of Sheliga et al. (2016). This stimulus comprises binocular Gabor patches that have opposite, unambiguous directions of drift in the two eyes, yet always have an ambiguous interocular phase disparity, producing pure IOVDs with no net CD. For the CD-only condition, the baseline Gabor phase changed randomly on each frame while the interocular phase difference was gradually incremented, producing pure CDs with no net IOVD. RESULTS & DISCUSSION. Sensitivity to CD improved gradually over the first 500 ms, whereas IOVD sensitivity saturated in less than half that time. These results support the hypothesis that CD and IOVD cues use separate underlying mechanisms, and that the former is much more sluggish (perhaps not being a true motion mechanism at all). Furthermore, we have introduced a class of stimuli that isolate one cue or the other while being otherwise matched along many other stimulus dimensions. Extensions to this paradigm will allow for better characterization of the sensory- and decision-related contributions to the time course of integration.
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