Properties of training-induced visual recovery in cortical blindness

University Of Rochester, Rochester NY

Investigators

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Abstract

? DESCRIPTION (provided by applicant): Cortical blindness (CB) results from damage to the primary visual cortex, presenting as a loss of vision in the contralateral visual field. Work from my lab and others have previously shown that visual training can recover simple and complex visual motion discriminations at trained, blind field locations in CB subjects. However, recovered contrast sensitivity and discrimination of fine direction differences are poor compared to those in intact portions of the visual field, suggesting that recovered vision is not fully functional. The main question addressed in this grant is: can these residual visual deficits be overcome in CB fields, both with respect to feature processing and spatial transfer of learning? To address this question, I have developed two specific aims to test (1) whether manipulating feature-based attention (FBA) or spatial attention (SA) will aid in overcoming residual visual deficits and (2) whether locations of training induced recovery are predicted by regions of spared retinotopic activity. In the first aim I will investigate the residual inability to perform fine direction discriminations following psychophysical training on coarse direction discrimination. I will attempt to overcome this impairment using FBA and SA coupled with visual discrimination training to recover visual performance. Both FBA and SA have been demonstrated in visual intact subjects to promote improvement of fine discrimination thresholds, and they will likely have the same effect in CB subjects. My second aim investigates the relationship between the visual field of CB subjects and retinotopic activity. Training-induced recovery is retinotopically localized to trained locations with respect to depth in the blind field, but not along the blind fild border. I will test the hypothesis that location of recovery can be predicted based on pre-training fMRI retinotopic maps and that vision can be recovered only in regions of the visual field where residual cortical activity is present. Humphrey perimetry and psychophysical measures of direction and orientation discrimination will be used to assess the spatial extent of training-induced recovery, which will be correlated with retinotopic maps obtained from fMRI. Finally, I will assess whether and to what extent retinotopic specificity of recovery deep into the blind fiel can be overcome by manipulating exogenous spatial attention. The proposed experiments will provide further insights into the properties of training-induced visual recovery in cortically blin fields, documenting the effects of attentional manipulations on training, investigating a possible mechanism by which training induced recovery occurs, and determining the spatial spread and limitations of recovered vision. A better understanding of these properties will not only improve treatment cortical blindness, but will also improve our understanding of plasticity within the adul visual system by studying to what extent visual function can recover following a large, permanent injury.