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Amanda M. Beers, Allison B. Sekuler, Patrick J. Bennett; The effects of inter-ocular contrast differences on binocular rivalry in younger and older observers . Journal of Vision 2014;14(10):1236. doi: 10.1167/14.10.1236.
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Beers et al. (VSS 2013) demonstrated that monocular dominance (MD) during binocular rivalry increases significantly with aging. Age differences in optical factors, such as sensitivity to inter-ocular contrast differences could provide an explanation. To investigate potential age-related changes in MD, we measured binocular rivalry in younger (aged 20-28) and older (aged 70-79) adults using pairs of orthogonal, oblique sine wave gratings that differed in contrast. In baseline conditions, rivalry was measured with equal stimulus contrasts (0.2 or 0.8) presented to both eyes. In the test condition, stimulus contrast was 0.2 in one eye and 0.8 in the other eye, with the eye viewing the higher contrast counter-balanced across trials. During each trial, participants reported their perceptual state by pressing buttons on a response box (the two exclusive percepts, mixed, and fading). MD was defined as the difference between the proportion of time a participant reported seeing each exclusive percept. MD in the baseline conditions was significantly greater in older than younger adults, supporting our previous findings. However, MD did not differ between age groups in the test condition. The introduction of an inter-ocular contrast difference of 0.6 caused MD to increase significantly in younger adults, whereas the contrast difference had an insignificant effect in older adults who already had shown strong MD in baseline conditions. A follow-up experiment measured binocular rivalry in younger adults with a wider range of inter-ocular contrast differences: 0, 0.2, 0.4, and 0.6. A contrast difference of 0.4 was needed to produce a level of MD that was approximately equivalent to that found in older adults with contrast-matched stimuli. These results demonstrate that a large difference in inter-ocular contrast is required to produce MD in younger adults that is equivalent to the MD found in older adults, suggesting neural changes in binocular vision with aging.
Meeting abstract presented at VSS 2014
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