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Tone task proves blind hear better

Early vision loss leads to keener hearing.

Blind people hear the differences between notes more precisely. Credit: © Photodics

It is no coincidence that so manypiano-tuners are blind. Folklore says their lack of sight gives them acutehearing, ideally suited to the task. Now neuroscientists in Canada have shownthat the sightless really do hear notes more precisely if they went blind whenthey were very young.

The idea that blindness can aid musical development is an old one, saysRobert Zatorre of McGill University in Montreal, a member of the study team.Ray Charles and Stevie Wonder, who both lost their sight at an early age, wereamong the twentieth century's most influential musicians.

But previous attempts to quantify the effect have met with mixedresults. Zatorre thinks this is because they did not take account of the age atwhich subjects went blind.

The researchers therefore divided their 14 blind subjects into twogroups: those who were blind at birth or lost their sight during the first twoyears of life, and those for whom blindness came later. The team also testedfully sighted people to see which of the three groups performed best atpitch-recognition tasks.

Subjects listened to "pairs of tones":../multimedia/tone.qt played oneafter the other, and were asked to decide whether the second was higher orlower than the first. The researchers varied both the difference in pitch ofthe two tones and their duration.

Note perfect

?Early blind? subjects outperformed the other groups in every way,continuing to make correct distinctions as the notes got either shorter orcloser in pitch. In fact, as the team reports in this week's Nature1, early-blind participants performed as well on the most rapid notesas sighted subjects did on notes ten times longer.

The blind subjects? ages ranged from 21 to 46, the researchers add. Thisshows that it is the age at which blindness occurs, rather than simply thenumber of years spent without vision, that determines sensitivity topitch.

In normal brains these connections are gradually eliminated. But in the early blind they might be preserved and used. Pascal Belin , University of Montreal

The discovery reveals a lot about the brain's capacity to reorganizeitself early in life, says study leader Pascal Belin of the University ofMontreal. He suspects that the visual cortex, the part of the brain thatusually deals with vision, can be used to process other sensory information ifgiven the chance.

At birth, the brain's centres for vision, hearing and other senses areall connected, Belin says. "In normal brains these connections are graduallyeliminated. But in the early blind they might be preserved and used."

That would allow regions such as the visual cortex to help with the jobof processing sounds. But, as the new research shows, there comes a point afterwhich is too late for the brain to adapt.

When all the senses are intact, the brain does not need lots ofconnections between sensory centres; the amount of information buzzing aroundwould be too confusing, says Zatorre. "It's like pruning a tree, you only keepthe branches that get more light," he says. But when your world is shrouded indarkness, a little extra brain power can be a big help.

References

  1. Gougoux F. et al.. Nature 430.309 2004

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University of Montreal

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Hopkin, M. Tone task proves blind hear better. Nature (2004). https://doi.org/10.1038/news040712-9

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  • DOI: https://doi.org/10.1038/news040712-9

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