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 (SEDcombo) and/or inhibition (SEDinhibition). While much has recently been revealed about SEDcombo and SEDinhibition, the relationship between them is still unknown.
Methods: We measured observers' foveal SEDcombo and SEDinhibition, 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 SEDcombo and SEDinhibition. An observer's interocular difference in contrast threshold was not always consistent with his/her SEDcombo and SEDinhihition, suggesting a partial binocular origin for the underlying imbalances. We also found stereo thresholds significantly increased with the magnitudes of SEDcombo, as well as with the magnitude of SEDinhibition.
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.