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Dyslexics struggle to recognise voices: Study

London: It`s not just the numbers they struggle with, people with dyslexia also find it hard to recognise familiar voices, a new study has claimed.

The study, published in the journal Science, is the first tentative evidence that small sounds in the human voice that vary between people are difficult for dyslexics to hear.

The scientists said that many people may have some degree of "voice blindness" and by studying it further would help them better understand how the human brain has evolved to recognise speech.

Because people who suffer from dyslexia are known to struggle with phonemes when reading, a team at Massachusetts Institute of Technology in the US wondered whether they might also struggle hearing them in people`s voices.

To investigate, the MIT team grouped 30 people of similar age, education and IQ into two camps: those with and without a history of dyslexia.

The subjects were then given a training to learn to associate 10 different voices — half speaking English and half speaking Chinese — with 10 computer-generated avatars. They were then later quizzed on how many of those voices they could match to the avatars.

Non-dyslexics outperformed people with a history of dyslexia by 40 per cent when listening to English. But this advantage vanished when the groups were listening to Chinese.

Understanding the mechanics of voice recognition is important, said the study`s lead author Tyler Perrachione, because it allows a listener to pinpoint a familiar voice above the hubbub of a crowded room.

Perrachione explained that very little is known about voice blindness, which is formally called phonagnosia.

"In reality, phonagnosia is probably much more common," he said, "but people who don`t recognise that voices sound different may not even realise they lack the ability to tell voices apart."

According to the researchers, humans rely on small sounds called phonemes to tell one person from another.

As we first try to form the word dog, for example, phonemes are the "duh"-"og"-"guh" sounds that our parents prompt us to make.

But as we master the ability to read, we become less reliant on recognising these sounds to read, and eventually stop noticing them, the researchers said.

Despite ignoring them, however, phonemes remain important for voice recognition. The tiny inflections in the way people pronounce phonemes gives a listener cues to tell one voice from another, they added.

Dorothy Bishop from the University of Oxford thinks that this is because "when [they] are listening to Chinese, it is a level playing field, because no one has learnt to hear [Chinese] phonemes".

The researchers think that dyslexics don`t have as comprehensive a phoneme sound library in their heads, and so they struggle when they hear phonemes spoken by unfamiliar voices because their "reference copy" isn`t as well-defined.

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