New brain clue to tone deafness discovered

Monday 25 June 2007

New brain clue to tone deafness discovered by Otago researchers
- Strong link found to deficits in spatial skills-

Why are some people tone deaf? This question has long puzzled scientists, but now New Zealand researchers have come up with surprising evidence about the brain processes involved.

A study by University of Otago psychology researchers shows, for the first time, that tone deaf people have poorer spatial skills than people who can distinguish musical notes in a normal way.

The researchers believe this difference may underlie problems in musical perception.

Their study, just published in the prestigious international journal Nature Neuroscience, found that people with tone deafness – known technically as amusia – perform significantly worse at a task requiring them to mentally rotate objects.

Study co-author Associate Professor David Bilkey of the Department of Psychology says true tone deafness affects around four per cent of the population.

“It’s not just the inability to carry a tune – people with amusia are often simply unable to tell differences between the musical notes they hear.”

“However, they have no problem detecting similar subtle changes in pitch that indicate questions in speech. Nor have studies with MRI scanners shown any abnormal processing in the auditory cortex of amusic brains,” he says.

Associate Professor Bilkey and fourth-year student Katie Douglas investigated whether tone deaf people have deficits in spatial representation and processing, which involves a different part of the brain.

They conducted experiments with 34 university students, including eight identified as amusical through a standard test. There were two control groups, one composed of 14 musicians and the other of 12 students from non-musical backgrounds.

When asked to perform a task involving mentally rotating three-dimensional objects made up of cubes – where they try to judge whether pairs of images are the same object rotated or mirror images – the amusical group made significantly more errors than the control groups, says Dr Bilkey.

Two further tests which involved performing tasks involving simultaneous melodic and spatial elements back up the initial finding, he says.

“In these particular tests, the important result was actually that the amusic group had fewer, rather than greater, difficulties with the tasks than the two control groups.

“This means that the people without amusia were experiencing more cognitive ‘interference’ when they had to simultaneously process spatial and melodic information.

“Although it involves different parts of the brain, the most familiar example of interference occurs when you try to pat your head and rub your stomach at the same time,” he explains.

The control groups’ greater susceptibility to interference during the tasks indicates that musical pitch processing may depend on the same cognitive mechanisms used to process spatial information, he says.

Not only do the findings provide an important insight into the possible causes of amusia, they also raise more general questions about the representation of music in the brain, he adds.

“We are all used to thinking about tones as being high or low, but these findings suggest that this could be more than just a metaphor.

“It might be based on something more fundamental to do with the way the brain stores information about the high and low notes in melodies.”

ENDS

© Scoop Media