Effect of Interocular Contrast Difference on Stereopsis in Observers With Sensory Eye Dominance

PURPOSE: We investigated how sensory eye dominance (SED) affects stereopsis when the half-images of random-dot-stereo stimuli had different interocular contrast. METHODS: We measured crossed and uncrossed stereo disparity thresholds and reaction time to seeing random-dot-stereograms with variable interocular contrast differences (ICD), where ICD = (log(10) [C(LE)] − log(10) [C(RE)]) = −0.4, −0.2, 0, 0.2, or 0.4 log unit. The mean contrast of the stimuli, (log(10) [C(LE)] + log(10) [C(RE)])/2, remained constant at 1.2 log unit to ensure that the measured effect was solely due to ICD. We also measured SED using, respectively, dichoptic horizontal sine wave gratings with different phases (revealing SED(combo)) and dichoptic vertical and horizontal gratings (revealing SED(inhibition)). RESULTS: Both measures of SED(inhibition) and SED(combo) revealed the observers had the same eye as dominant although the magnitudes differed. The observers had lower stereo thresholds and shorter stereo reaction time on stimuli with unequal interocular contrast when the non–sensory-dominant eye viewed the higher contrast half-image, suggesting a stimulus-compensating effect. We then estimated the ICD of random-dot-stereo half-images (compensating stimuli) that would lead to minimum stereo threshold (SED(stereo-threshold)) and reaction time (SED(stereo-RT)) based on the stereo performance and ICD relationship, and found that they were significantly smaller than SED(inhibition) and SED(combo). CONCLUSIONS: By linking SED(inhibition) and SED(combo) with the effect of ICD on stereopsis, we provided further support for the notion that the stimulus-compensating effect is mediated by the interocular inhibitory and interocular gain control mechanisms. Furthermore, the interocular contrast for SED(stereo-threshold) and SED(stereo-RT) can be potentially applied for improving stereopsis in individuals with SED.