How the deaf have better vision; the blind better hearing

November, 2010

Two recent studies point to how those lacking one sense might acquire enhanced other senses, and what limits this ability.

An experiment with congenitally deaf cats has revealed how deaf or blind people might acquire other enhanced senses. The deaf cats showed only two specific enhanced visual abilities: visual localization in the peripheral field and visual motion detection. This was associated with the parts of the auditory cortex that would normally be used to pick up peripheral and moving sound (posterior auditory cortex for localization; dorsal auditory cortex for motion detection) being switched to processing this information for vision.

This suggests that only those abilities that have a counterpart in the unused part of the brain (auditory cortex for the deaf; visual cortex for the blind) can be enhanced. The findings also point to the plasticity of the brain. (As a side-note, did you know that apparently cats are the only animal besides humans that can be born deaf?)

The findings (and their broader implications) receive support from an imaging study involving 12 blind and 12 sighted people, who carried out an auditory localization task and a tactile localization task (reporting which finger was being gently stimulated). While the visual cortex was mostly inactive when the sighted people performed these tasks, parts of the visual cortex were strongly activated in the blind. Moreover, the accuracy of the blind participants directly correlated to the strength of the activation in the spatial-processing region of the visual cortex (right middle occipital gyrus). This region was also activated in the sighted for spatial visual tasks.

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