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Jian Ding, Stanley Klein, Dennis Levi; Binocular combination in amblyopic vision. Journal of Vision 2009;9(8):274. doi: 10.1167/9.8.274.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia is a consequence of compromised binocular visual experience early in life. Here we investigate suprathreshold binocular combination in the amblyopic visual system, using a sensitive psychophysical paradigm adapted from Ding and Sperling (2006, 2007). On each trial, horizontal sine-wave gratings were presented independently to the two eyes using a mirror stereoscope. The two eyes' sine waves have identical spatial frequency of 0.68 cpd, but differ in contrast and have a 90 deg phase shift. The observer's task is to indicate the apparent location (phase) of the dark trough in the perceived cyclopean sine wave relative to a black horizontal reference line. The phase of the perceived cyclopean sine wave is used to compute the relative contribution of each eye to the cyclopean image. The relative contribution was measured as a function of interocular contrast ratios and base contrasts. Typically, for normal observers, the two eyes contribute equally when the two images have equal contrast. However, for amblyopic observers, we found that, to attain equal contribution, the non-dominant eye (NDE) needs to be presented with a higher contrast image (higher than one would predict from contrast sensitivities of the two eyes). The equal-contribution contrast ratios (NDE/DE, ECC ratios) were dependent on base contrast. At low base contrast, the binocular combination was almost a linear summation and the ECC ratios had lower values (near to 1 for some observers). When the base contrast increased, the binocular summation became more and more nonlinear and the ECC ratios became much larger (above 8) (interocular contrast gain control became more and more effective). The above results could be well predicted by Ding-Sperling gain control model if asymmetric gain control parameters are introduced. Conclusion. Interocular contrast gain control plays an important role in the dominant-eye suppression of the non-dominant eye in amblyopic binocular vision.
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