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Local motion processing limits fine direction discrimination in the periphery.

Mareschal I, Bex PJ, Dakin SC

UCL Institute of Ophthalmology, University College London, Bath Street, London EC1V 9EL, UK; Department of Optometry and Visual Science, City University, Northhampton Square, London EC1V 0HB, UK.

Visual sensitivity is reduced in the periphery for many discrimination tasks. Previously it has been reported that motion coherence thresholds are higher for dot stimuli presented in the periphery, a finding that could arise either from (a) impaired motion integration or (b) from motion integrators inheriting more noisy local directional signals. We sought to disentangle these factors using an equivalent noise paradigm. We report a deterioration in discrimination thresholds in the periphery that does not result from reduced visibility and is fully accounted for by an increase in local directional uncertainty with no change in sampling efficiency. Changes in motion coherence thresholds with stimulus eccentricity, measured using similar stimuli, exhibit a high degree of inter-subject variability.

Published 14 July 2008 in Vision Res, 48(16): 1719-25.
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