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Monday, October 25, 2010

Blind people have superior hearing and touch

Josef Rauschecker of Georgetown University lead a team of neuroscientists in comparing people who had been blind from birth to sighted people. The blind people had adapted parts of their visual cortex for use in hearing and touch, making those senses more acute.

The visual cortex is composed of about forty different modules. Each module is used for a specific task, such as orienting an object in space. For people with normal vision, these modules are only associated with vision, they aren’t activated to interpret sounds or other sensory input. People who are blind from birth use these modules differently.

The researchers hooked up twelve blind and twelve sighted people to an fMRI machine. While connected, the volunteers were asked to report from which direction certain sounds were emanating. In the blind but not the sighted subjects, the sounds activated the spatial module of the visual cortex. In fact, the more strongly that module was activated, the better the person was at figuring out the direction of the sound. When the same group of subjects was asked which finger was being gently stimulated, again the blind volunteers used parts of their visual cortexes to interpret the sensation.

The blind people were using not only the parts of the brain normally associated with sound or touch, but also the visual cortex, something sighted people cannot do. This gives the blind an edge in processing their other senses. It’s important to note that this study was done with people who had been blind from birth. In other words, their visual cortexes have never had any visual cues to process. It’s not clear to what extent the brain can be rewired in people who become blind later in life.

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