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Is another mystery of the human mind unravelling?

The successful British businesswoman, who is normal in every other way, is the first known case of someone being born with developmental phonagnosia, which leaves her unable to recognise even the voices of her own family.

Her condition is so profound that she often avoids using the telephone and struggles to identify people speaking on the radio.

Neuroscientists have now performed a series of tests and brain scans while asking her to listen to a range of recorded voices…

They found that while she was perfectly able to understand what was being said, she was unable to identify a speaker as someone she had been listening to a few minutes earlier.

Researchers are finding that her condition goes beyond a simple inability to remember voices, as she even has difficulty discriminating between two voices played back to back.

Brain scans taken as she listened to voices showed her brain reacted differently from most people’s, suggesting it is unable to process information from voices about speaker identity.

Researchers are also testing another man who they believe suffers from the same condition, but have yet to confirm his diagnosis.

Professor Pascal Belin, a cognitive neuroscientist at Glasgow University, said: “Identifying voices is surprisingly important for people, especially on the telephone.

“We can usually tell who someone is on the telephone, even if the line is bad, from just a word. But people with phonagnosia are not able to do this.

“Recognising a voice relies upon the acoustic differences between voices such as the melody or pitch of a voice and the tone, which is directly related to the size of the vocal chord and tells us about whether the speaker is big or small.

“There are a range of other features such as hoarseness, roughness, breathiness of the voice, which have to do with the airflow over the vocal chords, and these all combine to make our voices distinctive.”

Professor Belin has been working with Dr Brad Duchaine, from University College London’s Institute of Cognitive Neuroscience, who was the first to recognise that the woman, identified only as KH, suffered from phonagnosia.

She came forward after reading about work that Dr Duchaine had been doing on prosopagnosia, a condition where people are unable to recognise and remember faces.

The woman, who is a management consultant, agreed to take part in a series of tests and has now undergone brain scans in Glasgow.