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Alby Richard, Benjamin Thompson, Robert Hess, Craig Aaen-Stockdale, Christopher Pack; Motion direction discrimination in strabismic amblyopia: Effects of stimulus contrast and size. Journal of Vision 2009;9(8):1057. doi: https://doi.org/10.1167/9.8.1057.
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© ARVO (1962-2015); The Authors (2016-present)
It is established that amblyopic eyes are impaired at motion tasks requiring segregation of signal from noise; yet the fidelity of amblyopic motion processing in the absence of external noise is unclear. We investigated the effects of stimulus size and contrast on the ability of strabismic amblyopes to detect the motion direction of briefly (70ms) presented Gabor patches. The stimuli had a spatial frequency of 0.5cpd, and the size was varied from 5.3° to 18.5°. Two contrasts were tested for all stimulus sizes: a high contrast of 98% was used for all participants, and a low contrast of 1.5% was used for the control participants. The low contrast varied for the amblyopic observers as the stimulus had to be visible to the amblyopic eye. The stimulus was a two-frame motion pulse, constructed by shifting the phase of a Gabor patch on consecutive frames. Measurements were made under both monocular and binocular viewing conditions for 5 amblyopic and 5 control participants. Amblyopic eyes were impaired relative to control eyes for the monocular high contrast condition but did not differ from fellow eyes. The effect of size was consistent across all eyes for the high contrast stimulus. For the monocular low contrast condition, amblyopic eyes showed a pronounced curtailment in the beneficial effects of spatial summation on motion discrimination, relative to control eyes and the fellow eyes. For controls, binocular viewing greatly increased the beneficial effects of spatial summation relative to monocular viewing. No such effects were observed for amblyopic observers, suggesting that the amblyopic eye did not contribute to task performance under binocular viewing conditions. Interestingly, monocular performance for the amblyopic fellow eye was superior to monocular performance for either eye of controls. Our results suggest a specific deficit in spatial summation of low contrast motion information in strabismic amblyopia.
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