Braille Reading & Adaptive Plasticity in the Human Brain

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This proposal is designed to understand the functional architecture supporting behavioral adaptations to blindness. It is likely that visual cortex plays a major role because its activity increases in blind people during various non-visual perceptual and cognitive tasks. In addition, disruption of occipital cortex in blind people impairs Braille reading, indicating a likely role in this critical skill. Blind people also exhibit superior perceptual processing of non-visual stimuli. Based on these findings, we will explore three hypotheses: (1) Reorganized visual cortex respects principles of hierarchical processing and domain specialization found in sighted people that are related both to retinotopic visual areas and to the fovea-periphery eccentricity axis. (2) Reorganized visual cortex contributes to perceptual and cognitive behaviors in blind people. (3) Enhanced performance noted in blind people on a variety of tasks correlates with and perhaps is causally related to altered response dynamics outside visual cortex. An integrated set of fMRI studies in congenitally/early blind, adventitously blind, and normally sighted people will be used to assess these hypotheses. The results from two studies will be analyzed to reveal the degree to which early visual areas and/or regions of foveal representation selectively process lower level tasks like sublexical processing or stimulus amplitude detection, and whether higher visual occipito-temporal areas and/or parafoveal/peripheral eccentricity representations selectively process more complex tasks like semantic categorization or sensory working memory. The results from another two studies will be analyzed to reveal the degree to which overlapping or subparts of occipito- temporal areas and/or parafoveal/peripheral eccentricity representations process higher level recognition memory for non-verbal and verbal items. Submodality separation in reorganized visual cortex will be assessed from studies involving stimulation with tactile vibrations or auditory tones in separate experiments. In all experiments blood oxygen level dependent response dynamics in visual and selective non-visual areas will be quantitatively analyzed and correlated with performance to determine likely causal relationships.