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Zahra Hussain, Ben Webb, Paul McGraw; The effects of eccentricity and separation on interocular positional judgements in amblyopia. Journal of Vision 2015;15(12):266. doi: https://doi.org/10.1167/15.12.266.
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© ARVO (1962-2015); The Authors (2016-present)
Positional judgements are distorted in the central and peripheral visual field of amblyopic subjects. We have previously shown that bisection and alignment of spatially separated targets is more impaired near the fovea than in the periphery. Here, we examined whether the pronounced central deficit is due to foveal presentation per se, or due to the smaller separation of targets at smaller eccentricities. Observers performed a two-dimensional free-localization task along three axes (diagonal, horizontal and vertical). Each positional judgement comprised simultaneous bisection and alignment of a comparison stimulus relative to a target stimulus, using the central fixation cross as a reference. Target eccentricity (1 - 7 deg) and target-comparison separation (0.76 - 13 deg) were varied independently. The stimuli were broadband dots viewed dichoptically and the fixation cross was viewed by both eyes. Visually normal and amblyopic observers were tested. We calculated the precision (standard deviation) and bias (mean displacement) of responses as a measure of performance in all conditions. For normal observers, performance declined with eccentricity, and showed a modest dependence on stimulus separation at each eccentricity. Conversely, amblyopic observers showed a larger dependence on stimulus separation than on eccentricity: Although performance of amblyopes was poorer in the central visual field compared to the periphery (consistent with previous findings), performance was disproportionately worse at small stimulus separations at all eccentricities. These results suggest the presence of interocular interference for spatially proximal stimuli throughout the near-peripheral visual field in amblyopia. The strength of interocular suppression in amblyopia may depend less on visual field position than on the distance between competing stimuli viewed by both eyes.
Meeting abstract presented at VSS 2015
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