There are more than 3.5 million Americans with low vision, most of whom have reading difficulties. The primary purpose of this proposal is to evaluate the importance of perceptual training and plasticity of the visual system to reading rehabilitation, particularly for people with macular degeneration.Our research indicates that decrease in the size of the visual span is a key factor explaining reduced reading speed in low vision. The visual span is the number of letters that are identified in a single glance during reading. We have found that perceptual training in normal peripheral vision can enlarge the visual span with a corresponding increase in reading speed. In a series of psychophysical studies, we will assess the relevance of this finding for rehabilitation in young and old subjects with normal and low vision. We will also ask how spatial attention and positional signals influence the size of the visual span.The potential for vision rehabilitation depends on the plasticity of the visual brain following eye disease. In a series of fMRI experiments, we will study low-vision subjects to 1) evaluate changes in retinotopic mapping in the visual cortex, and 2) ask whether visual cortex participates in tactile perception.In a third series, we will conduct secondary analyses on two large sets of well-characterized low-vision reading data (MNREAD) test), from cataract and macular-degeneration patients. We will use these data to 1) analyze the relationships between properties of reading vision and clinical measures of visual impairment; 2) develop a new reading ability scale for quantifying overall reading capacity, and 3) analyze the relationship between reading ability and important non-visual factors including cognitive status and mental-health status.
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