Sensory input to the visual system arises from two separate channels (left and right eyes), yet we experience a single, unitary visual world that belies little hint of the dual monocular origins of that experience. This transformation from two monocular views to stable binocular single vision is the manifestation of important neural processes that give rise to significant improvements in visual perception, including stereoscopic depth perception and binocular contrast summation. In cases of sensory eye dominance (SED), a condition where one of the two eyes contributes more strongly to the binocular percept than the other, these gains can be muted or, in extreme instances, completely thwarted. Under these conditions, vision with two eyes is no better than with one, and in some instances is worse owing to monocular competition. In addition to arising from differences in monocular processing, asymmetric contributions from the left and right eyes may stem from processes involved in combining neural signals from the two eyes. The local nature of binocular combination suggests, moreover, that SED may vary idiosyncratically throughout the visual field.
Aim 1 will investigate how patterns of SED vary across visual field locations, and will test for influences of regional SED patterns on binocular function. Then, extended monocular patching, known to strengthen one eye's contribution to the binocular percept, will be utilized to learn whether altering these SED maps can lead to improved binocular function by counteracting the neural processes putatively responsible for SED. Following psychophysical measurements in Aim 1, Aim 2 will apply functional magnetic resonance imaging (fMRI) to test predictions stemming from a simple neural model of binocular integration. This model predicts increased neural activity (and thus larger BOLD signal responses) to dominant eye stimulation and epochs of perceptual dominance (during binocular rivalry) at locations of strong SED imbalance. An fMRI study will investigate whether this is due to stronger drive of monocular input neurons and/or greater engagement of inhibitory interneurons mediating binocular contrast gain control. By studying this network under monocular, binocular fusible, and binocular rivalry conditions, the stage of processing giving rise to SED can be isolated, while also revealing how underlying mechanisms vary functionally throughout the visual field. This research project will provide important training opportunities focused on psychophysics, neural modeling and neuroimaging. Working closely with proposed research mentor Randolph Blake and interacting with others in the Vanderbilt Vision Research community offers a unique opportunity to expand the applicant's expertise in visual neuroscience. Results from the proposed research can potentially lead to translational applications in the diagnosis and treatment of binocular visual disorders, offering additional and important training in linking vision research to clinical practie. This will act as a launch pad for the applicant's career as an independent scientist working on clinically relevant problems of human vision.

Public Health Relevance

Stable binocular vision and stereopsis arise consequent to effective neural integration of sensory information from the two eyes. This proposal seeks to better understand the neural mechanisms that perform this integration, and how that process is impacted when integration is unbalanced between the eyes. Results from the proposed research can lead to a deeper understanding of binocular visual disorders (e.g. strabismic amblyopia) and to treatment of conditions involving differential refractive correction of the two eyes (e.g. monovision).

National Institute of Health (NIH)
National Eye Institute (NEI)
Postdoctoral Individual National Research Service Award (F32)
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Special Emphasis Panel (ZRG1)
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Agarwal, Neeraj
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Vanderbilt University Medical Center
Schools of Arts and Sciences
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Dieter, Kevin C; Sy, Jocelyn L; Blake, Randolph (2017) Individual differences in sensory eye dominance reflected in the dynamics of binocular rivalry. Vision Res 141:40-50
Dieter, Kevin C; Melnick, Michael D; Tadin, Duje (2016) Perceptual training profoundly alters binocular rivalry through both sensory and attentional enhancements. Proc Natl Acad Sci U S A 113:12874-12879