Tone task proves blind hear better
Early vision loss leads to keener hearing.
It is no coincidence that so many piano-tuners are blind. Folklore says their lack of sight gives them acute hearing, ideally suited to the task. Now neuroscientists in Canada have shown that the sightless really do hear notes more precisely if they went blind when they were very young.
The idea that blindness can aid musical development is an old one, says Robert 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, were among the twentieth century's most influential musicians.
But previous attempts to quantify the effect have met with mixed results. Zatorre thinks this is because they did not take account of the age at which subjects went blind.
The researchers therefore divided their 14 blind subjects into two groups: those who were blind at birth or lost their sight during the first two years of life, and those for whom blindness came later. The team also tested fully sighted people to see which of the three groups performed best at pitch-recognition tasks.
Subjects listened to pairs of tones played one after the other, and were asked to decide whether the second was higher or lower than the first. The researchers varied both the difference in pitch of the two tones and their duration.
‘Early blind’ subjects outperformed the other groups in every way, continuing to make correct distinctions as the notes got either shorter or closer in pitch. In fact, as the team reports in this week's Nature1, early-blind participants performed as well on the most rapid notes as sighted subjects did on notes ten times longer.The blind subjects’ ages ranged from 21 to 46, the researchers add. This shows that it is the age at which blindness occurs, rather than simply the number of years spent without vision, that determines sensitivity to pitch.
University of Montreal
The discovery reveals a lot about the brain's capacity to reorganize itself early in life, says study leader Pascal Belin of the University of Montreal. He suspects that the visual cortex, the part of the brain that usually deals with vision, can be used to process other sensory information if given the chance.
At birth, the brain's centres for vision, hearing and other senses are all connected, Belin says. "In normal brains these connections are gradually eliminated. But in the early blind they might be preserved and used."
That would allow regions such as the visual cortex to help with the job of processing sounds. But, as the new research shows, there comes a point after which is too late for the brain to adapt.
When all the senses are intact, the brain does not need lots of connections between sensory centres; the amount of information buzzing around would be too confusing, says Zatorre. "It's like pruning a tree, you only keep the branches that get more light," he says. But when your world is shrouded in darkness, a little extra brain power can be a big help.
- Gougoux F. et al.. Nature430.309 2004