A Wired article, Red, Blue, Green and Other Sounds, describes two studies that indicate that the region of the brain that processes sight remains alive and active even in blind people.

It opens up two other interesting avenues of consideration. I remember reading, I think in an Oliver Sachs book, that experiments done to correct vision in people blind at birth resulted in traumatic outcomes. The notion was that there is a window of opportunity for the vision systems early in the developmental cycle -- and if it's missed, as with language acquisition, the person can never properly make sense of the grammar of vision (e.g., depth perception). If this is true, then I would infer that the substitution of sound for visual input would fail when applied to adults blind from birth.

The other fascinating angle here is the relationship to synesthesia, a naturally occurring blurring of sense boundaries that many people experience. Numbers are colored, sounds have shapes, feelings have textures, and so forth. Wired had another article about this last month, The Man Who Lives in a Rainbow. This suggests that people with synesthesia never developed the fully compartmentalized routing of sensory data to only one processing system.

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