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Eunice Yang, Michael Silver, Dennis Levi; Impaired mechanisms of suppression in amblyopia. Journal of Vision 2013;13(9):44. doi: 10.1167/13.9.44.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia is often accompanied by suppression of visual signals from the weaker eye. Physiological studies of amblyopia suggest that intracortical inhibition may play a role in mediating amblyopic suppression. We investigated whether other suppressive phenomena tied to intracortical inhibition are also impaired in amblyopia. Specifically, we measured the magnitude of surround suppression, overlay suppression, and interocular suppression in amblyopes and healthy controls, using well-established psychophysical measures. When a stimulus with surround mask was presented to amblyopes’ dominant eye (DE), perceived contrast of that stimulus was reduced, and the magnitude of surround suppression was comparable to that of controls. In contrast, surround suppression associated with the amblyopic eye (AE) was significantly stronger in comparison to the DE and to control subjects. In our overlay suppression task, contrast detection thresholds were measured for a Gabor patch embedded in noise relative to when it was presented alone. Elevations in contrast thresholds were significantly lower when the masked Gabor patch was presented to the AE in comparison to the DE, consistent with previous findings. In contrast, overlay suppression measured with amblyopes’ DE was comparable to that of controls. Finally, we used flash suppression to measure elevations in contrast increment discrimination thresholds for an eye when it was suppressed relative to when it was dominant. In line with previous studies, amblyopes showed a significant imbalance in interocular suppression relative to controls, which was attributed to diminished flash suppression of the DE by the AE. The magnitude of surround suppression and to a weaker extent, interocular suppression was predictive of the severity of amblyopia, as indexed by interocular differences in acuity. Our results are consistent with physiological evidence that amblyopia is associated with heightened GABAergic inhibition and that surround and interocular suppression, but not overlay suppression, are most likely mediated by intracortical inhibition.
Meeting abstract presented at VSS 2013
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