On Sensory Eye Dominance Revealed by Binocular Integrative and Binocular Competitive Stimuli

PURPOSE: Two core processes underlie 3-D binocular vision. The first, a binocular combination/summation process, integrates similar feature signals from the two eye channels to form a binocular representation. The second, a binocular inhibitory process, suppresses interocular conflicting signals or falsely matched binocular representations to establish single vision. Having an intrinsic interocular imbalance within one or both processes can cause sensory eye dominance (SED), related to imbalances of combination (SED(combo)) and/or inhibition (SED(inhibition)). While much has recently been revealed about SED(combo) and SED(inhibition), the relationship between them is still unknown. METHODS: We measured observers' foveal SED(combo) and SED(inhibition), respectively, with a pair of dichoptic horizontal sine wave gratings with different phases and binocular rivalry stimulus with vertical and horizontal gratings. We then measured horizontal and vertical monocular contrast thresholds using sinusoidal grating stimuli, and stereo thresholds using random-dot stereograms. RESULTS: There exists a strong correlation between SED(combo) and SED(inhibition). An observer's interocular difference in contrast threshold was not always consistent with his/her SED(combo) and SED(inhihition), suggesting a partial binocular origin for the underlying imbalances. We also found stereo thresholds significantly increased with the magnitudes of SED(combo), as well as with the magnitude of SED(inhibition.) CONCLUSIONS: Our findings suggest a common origin for interocular imbalance in the two different binocular processes and that both types of sensory eye dominance are significant factors in impeding stereopsis.