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Isabelle Garzorz, Tom Freeman, Marc Ernst, Paul MacNeilage; The Vestibular Aubert-Fleischl Phenomenon. Journal of Vision 2016;16(12):1201. doi: 10.1167/16.12.1201.
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To estimate object speed in the world, retinal motion must be summed with extra-retinal signals that tell about the speed of eye and head movement. Prior work has shown that differences in perceptual estimates of retinal and oculomotor (eye) speed lead to effects such as the Aubert-Fleischl phenomenon (AF) in which pursued targets are typically perceived to move slower than non-pursued ones. Here we demonstrate an analogous phenomenon, the vestibular AF, that results from differences in perceptual estimates of retinal and vestibular (head) speed. Subjects seated on a hexapod motion platform viewed a stereo visual scene consisting of a field of red spheres and a fixation point. In a 2IFC task, subjects indicated the interval in which the spheres moved faster in the world. In the oculomotor condition, one interval involved smooth pursuit with no retinal motion, the other stationary eyes with only retinal motion (i.e. classic AF paradigm). In the vestibular condition, the former was replaced by a "vestibular pursuit", i.e. subjects were passively rotated at the same speed as the spheres and fixation point. Yaw rotations had a raised cosine velocity profile with 1 sec duration and displacement of 3, 6, or 9 deg for the reference movement. Retinal speed was varied following an adaptive procedure to find the point of subjective equality (PSE), i.e. the retinal speed at which world-centered object speed was perceived equal to that during the oculomotor or vestibular interval. The ratio of retinal to oculomotor or vestibular speed at PSE was smallest in the vestibular condition, indicating that the vestibular AF is significantly stronger than the classic AF; this ratio did not depend on reference speed. We model the vestibular AF in the same probabilistic framework that has been used to characterize the classic AF (Freeman et al 2010).
Meeting abstract presented at VSS 2016
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