Marina Bedny, Johns Hopkins University
Insights into contributions of nature and nurture to the human mind and brain from studies with blind individuals.
British empiricist philosophers, such as Locke and Hume, conducted thought experiments on blindness. They concluded that 'visual' concepts, such as color, were inaccessible to blind people and used this to support the claim that mental representations originate from sensory experience. The question of how sensory experience contributes to the mind and brain remains central to modern cognitive and neuroscientific theories. Empirical studies with blind individuals reveal some surprises with respect to these theories.“Visual” concepts and their neural basis turn out to be largely preserved in blindness. Through linguistic communication and inference, blind individuals acquire rich structured knowledge of light events (glimmer), animal appearance and colors (blue). By contrast, cortical systems that evolved for visual perception undergo dramatic functional reorganization. In blindness ‘visual’ cortices participate in higher-cognitive functions, including language, numerical processing and non-verbal executive control. Studies of resting-state connectivity suggest that plasticity occurs via takeover of ‘visual' cortex by top-down higher-cognitive networks in fronto-parietal cortices. This evidence suggests that human cortex is more cognitively flexible than previously realized and challenges the notion that sensory systems are more “hard-wired” than higher-cognitive ones. Studies of blindness support a view of the human cortex as a collection of specialized but powerful learning mechanisms, each with an evolutionarily constrained “window” onto the world.