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Marina Danilova, J.D. Mollon; The comparison of spatially separated stimuli: judgments of speed. Journal of Vision 2017;17(7):21. doi: 10.1167/17.7.21.
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© ARVO (1962-2015); The Authors (2016-present)
We consider a theoretically interesting problem: How are stimuli compared when they fall at different, widely separated, positions in the visual field? Previously we have shown that thresholds for discriminating spatial frequency are similar whether targets are juxtaposed or are separated by up to 10 deg (eccentricity being held constant) - and even if the targets fall in opposite hemifields [1,2].
In the present experiments, we measured thresholds for comparing speed in two patches of moving dots. The patches lay on an imaginary circle of 5 deg radius centered on fixation, and presentations were too brief to allow eye movements. The separation between the centers of the patches varied from 2 to 10 deg.
At slow speeds, observers had lowest thresholds when the moving arrays were juxtaposed; but at medium speeds (6–8 deg/s) there was rather little variation in threshold with separation. It is implausible that the comparison depends on dedicated ‘comparator neurons’, i.e. higher-order cells that would draw inputs from pairs of lower-order cells that signal speed in local retinal regions; and we postulate instead a ‘cerebral bus’ that carries abstract representations of separated stimuli [1,2].
Meeting abstract presented at the 2016 OSA Fall Vision Meeting
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