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pan zhang, Qing He, Zhong-Lin Lu, Chang-Bing Huang; Monocular attenuation and binocular inhibition underlie effects of unilateral mean luminance on binocular combination. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3003.
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To determine the mechanisms underlying its effects on binocular functional balance, we investigated the impact of unilateral mean luminance on binocular phase and contrast combination within a multi-channel contrast gain control (MCM) framework (Huang et al, 2010,2011).
We adopted binocular contrast and phase combination paradigm in this study, in which a stereoscope is used to present two gratings (test gratings), with the same spatial frequency (1 cpd) but different contrasts and phases, to the two eyes. By requiring observers to adjust the phase and contrast of the probe grating, presented to only one eye, to match those of the cyclopean percept, the contrast and phase of the cyclopean percept is measured as functions of the contrast in the attenuated eye (32%), the ratio of the grating contrasts in the un-attenuated and attenuated eyes (δ=[0 0.2 1]), the phase difference between the two test gratings (45 degrees), the eye in which the probe grating resides, and the dichoptic configuration, a total of 12 different conditions.
We found that the perceived contrast and phase of the cyclopean image varied significantly with interocular contrast ratio and the magnitude of luminance difference. Analysis based on MCM (Huang et al, 2010, 2011) revealed that reducing the mean luminance (decreasing 90% for 1ND and 99% for 2ND) with a neutral density filter in one eye leads to monocular attenuation of signal in the attenuated eye (12.4% for 1ND and 53.9% for 2ND relative to baseline) as well as stronger interocular inhibition from the un-attenuated eye to the attenuated eye (135% for 1ND and 8517% for 2ND relative to baseline). Interestingly, two-hour luminance adaptation greatly relieved attenuated monocular signal (signal increased 25.7% relative to the no-adaptation condition with 2ND) and interocular inhibition (decreased by 53.5% relative to the no-adaptation condition with 2ND) due to imbalanced luminance received by the two eyes.
We conclude that both monocular and intraocular mechanisms underlie the effects of unilateral mean luminance on binocular function. The findings may have major implications for the studies of binocular vision in both normal and abnormal populations.
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