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Sydney Gilbert, Daryn Blanc-Goldhammer, Paul Dassonville; The Double-drift Illusion Affects Both the Perception of Where the Target IS and the Memory of Where it WAS.. Journal of Vision 2017;17(10):422. doi: https://doi.org/10.1167/17.10.422.
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© ARVO (1962-2015); The Authors (2016-present)
In the double-drift illusion, the perceived trajectory of a moving Gabor is biased by its internal local motion (Tse & Hsieh, 2006; Lisi & Cavanagh, 2015). It remains unclear whether this distorted trajectory is caused by erroneous perception of the current location of the stimulus, erroneous memory of its previous locations, or both. Blanc-Goldhammer et al. (VSS 2016) asked observers to compare the location of the trajectory's start (or end) to a probe presented just before (or after) a single sweep of a double-drift stimulus, and demonstrated that the illusion caused a small distortion of the perceived starting location (biased in a direction opposite the local motion) and a larger (~3X) distortion of the perceived ending location (biased in the same direction as the local motion). In the present experiment, we assessed the change in the observer's memory of the trajectory's starting location, by asking the observer to compare the onset location with a probe that could be presented before or after motion onset (-250, 0, 250, 500 or 1000ms). Participants maintained fixation in the center of the screen while a Gabor containing leftward, rightward, or no internal motion traveled upward for 500ms in the periphery; the global motion of the stimulus was adjusted for each observer to offset the effects of the illusion so that the perceived trajectory was purely vertical. For probes presented 250ms before motion onset, the local motion induced a small but significant distortion of the perceived starting location. This bias grew significantly with later probe presentations, reaching a plateau for delays of 250ms or longer. These findings suggest that at least a portion of the distortion in the trajectory of a double-drift stimulus is caused by a bias in the memory of its earlier locations, which are pushed in a direction opposite the local motion.
Meeting abstract presented at VSS 2017
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