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Mark Edwards, John Greenwood, Alyssa Morse, Carlos Cassanello; Perception of bidirectional transparent-motion requires a bimodal population response. Journal of Vision 2013;13(9):973. doi: https://doi.org/10.1167/13.9.973.
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© ARVO (1962-2015); The Authors (2016-present)
The perception of bidirectional transparent motion involves the detection of two global directions within the same spatial region. It has been proposed that the neural population activity mediating this percept depends upon the angular separation between the two directions: bimodal activity-peaks for large angular differences and broad uni-modal for angles below 90[sup]o[/sup] (Nature Neuroscience 2000, 270-276). This model is based upon the average tuning bandwidths of V5/MT cells. This means that uni-modal population activity can underlie the perception of both uni- and bi-modal motion, and the proposed model does not state how the visual system could differentiate between the two. It would be simpler if transparency was always represented by bi-modal activity and uni-modal activity always indicated uni-directional motion. This could be the case if a subset of V5 cells, that have tighter tuning bandwidths, mediate motion transparency. We sought to determine the underlying population response via adaptation to transparent motion with various angular separations and the subsequent pattern of elevation in unidirectional motion thresholds. Stimuli consisted of either global-plaid or global-Gabor stimuli, which consists of multiple static apertures that contain either plaids or Gabors, respectively (JoV 2009 1-25). The minimum angular separation between the motion directions required to perceive transparency was established and adaptation was conducted at sub-threshold, threshold and supra-threshold (but below 90[sup]o[/sup]) angular separations. In order to tap the population activity at the global-motion level, the apertures in the adapting and test stimuli were in different locations. Sub-threshold angular separations resulted in a uni-modal pattern of unidirectional threshold elevation while threshold and supra-threshold angular separations resulted in bimodal patterns of threshold elevation. The results support the notion that the perception of transparent-motion requires bimodal activity at the global-motion level.
Meeting abstract presented at VSS 2013
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