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Thaddeus B. Czuba, Bas Rokers, Alexander C. Huk, Lawrence K. Cormack; Distinct binocular mechanisms for 3D motion perception. Journal of Vision 2010;10(7):817. doi: 10.1167/10.7.817.
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© ARVO (1962-2015); The Authors (2016-present)
The perception of 3D motion relies on two binocular cues, one based on changing disparities over time (CD cue), and one based on the interocular velocity differences (IOVD cue). While both cues are typically present when a real object moves through depth, the CD cue is easy to isolate and has therefore received the most attention. More recently, however, the IOVD cue has been (behaviorally) isolated and shown to play a strong role in the perception of 3D motion.
We probed the mechanisms responsible for 3D motion using a standard motion adaptation paradigm. Observers adapted to random dot motion directly towards or away from them. The strength of the resulting motion aftereffect was determined from the shift in the psychometric function relating dot motion coherence to perceived direction. The shifts in 3D motion thresholds were extremely large–around 45% coherence–double that of frontoparallel aftereffects measured using otherwise identical 2D motion stimuli. These results (and those from a variety of control conditions) are inconsistent with a simple inheritance of 2D aftereffects and reveal adaptation of a unique 3D motion mechanism.
We next adapted observers to 3D motion stimuli that contained the isolated CD or IOVD cue, or combined both cues (like most real-world motion). Each aftereffect was measured using an identical combined-cue variable motion coherence stimulus. Adaptation to either the combined-cue or IOVD-isolating stimuli resulted in the same large aftereffects seen in the first experiment, while adaptation to the CD-isolating stimulus produced aftereffects less than half as large.
These motion aftereffects reveal distinct representation of 3D directions of motion, indicate that separate mechanisms exist for processing the disparity- and velocity-based cues, and support recent work showing that, under many conditions, the velocity-based cue plays a surprisingly fundamental role in 3D motion perception.
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