Loss of sight and enhanced hearing: A neural picture

Stevie Wonder and Ray Charles are often cited as anecdotal evidence that blindness confers superior musical ability. In fact, systematic studies have shown that blind persons perform nonvisual tasks better than those with sight. Neuroimaging studies have suggested that areas of the brain normally devoted to vision become active when blind persons perform nonvisual tasks, but much remains to be learned about the nature and extent of this phenomenon. A new study published in the open-access journal PLoS Biology finds a strong correlation between superior sound localization skills and increased activity in the brain's visual center.

The task of localizing sound--which requires integrating information available to one ear only (monaural sounds available, for example, when one ear is plugged) or information derived from comparing sounds binaurally--is particularly suited to investigating the neural remapping that seems to follow vision loss. In a previous study, Franco Lepore and colleagues showed that people who lost their sight at an early age could localize sound, particularly from monaural cues, better than those who could see. These findings suggested that areas of the brain normally dedicated to processing visual stimuli (the visual cortex, located at the back of the brain in the occipital lobe) might play a role in processing sound in these individuals.

In the new study, the authors hypothesized that if visual cortex recruitment bolstered auditory function in some individuals, then visual cortex activity would correlate with individual differences in performance, and the degree of activity should predict such differences. Nineteen people--seven sighted and twelve who lost their sight at an early age--were placed in an echo-free chamber and asked to indicate where a sound was coming from, using either one (monaural) or both (binaural) ears.

Only the blind individuals with superior localization skills showed increased activity in the visual cortex while performing monaural localization tasks. Whether the enhanced auditory performance reported here simply reflects increased efficiency of auditory processing or indicates "supranormal" powers, Lepore and colleagues argue that their results show that the visual cortex is "specifically recruited to process subtle monaural cues more effectively." It will be interesting to learn whether blind persons can recruit visual centers for other auditory tasks or to help them navigate the world without sight.

Citation: Gougoux F, Zatorre R, Lassonde M, Voss P, Lepore F (2005) A functional neuroimaging study of sound localization: visual cortex activity predicts performance in early-blind individuals. PLoS Biol 3 (2): e27.

CONTACT: Franco Lepore
University of Montreal
C.P. 6128, Succursale Centre-ville
Montréal, Québec CA H3C 3J7
1-514-343-2341
1-515-343-5787 (fax)
franco.lepore@umontreal.ca

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