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High notes really are high

June 24, 2007 By Kerri Smith This article courtesy of Nature News.

Perception of pitch and spatial orientation are linked.

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The way that people talk about 'high' and 'low' notes makes it sound as though musical pitch has something to do with physical location. Now it seems there may be a reason for this: the same bit of our brain could control both our understanding of pitch and spatial orientation.

The result comes from a study of tone-deaf people — also known as 'amusics' — which shows that they have poorer spatial skills than those who have no problem distinguishing between two musical notes.

Amusics are unable to tell whether a particular musical note is higher or lower than another. The condition has puzzled neuroscientists, because the way in which the brains of amusics process auditory information seems to be no different from normal.

Researchers from the University of Otago in New Zealand were keen to investigate. David Bilkey and his student Katie Douglas (who, as a member of the New Zealand Youth Choir, is particularly interested in how the brain processes music) had noticed that music is often described using spatial references, such as 'high' and 'low' notes — with higher notes literally sitting higher on a stave. The same is true in many different languages. So they decided to test the spatial skills of amusic people.

"The question was whether the relationship was just a metaphor or something more than that," says Bilkey.

He and Douglas asked volunteers to mentally rotate an object, and click on a picture of how it would look when rotated. Amusic subjects made more than twice as many errors than either of the two control groups — one made up of musicians, the other a group with little musical training. The results are reported in Nature Neuroscience1.

"We were really surprised. The hypothesis that spatial processing was the underlying problem was a long shot," Bilkey says. Most studies of amusia have focused on pitch processing as the fundamental deficit, says Tim Griffiths, a neurologist at Newcastle University in the UK.

In chorus

The researchers went on to see if their volunteers could perform both tasks — pitch discrimination and object rotation— at the same time.

The control groups found this hard, and took much longer to mentally rotate objects when they also had to discriminate between two notes. This is presumably because the tasks interfered with each other. "One possibility is that pitch is encoded in parts of the brain that also encode spatial information," suggests Bilkey. This would increase the workload for these brain regions in normal people, slowing them down.

But amusic subjects were much less affected by having to do these tasks simultaneously. Because they were pretty much unable to tell the musical notes apart, their brain was free to work on the spatial task.

One brain region that might be doing the work is an area in the parietal lobe called the intraparietal sulcus (IPS), says Bilkey, which is known to be involved in processing music, spatial information and numbers.

Space training

Given the relationship between amusia and spatial skill, does this mean that improving one might boost the other? The researchers don't yet know.

It has been previously shown that people with many years of musical training are better at spatial tasks, Bilkey says. But it's not clear how this relationship works, or what causes what.

So it's unknown whether wannabe musicians would benefit from rotating shapes in their heads. Or whether amusic people would benefit from spatial skills training. Griffiths has met many amusics, and is sceptical. "I'm not sure if auditory training would help people, let alone spatial training," he says.

References

  1. Douglas K.& Bilkey D. Nature Neurosci., 10. 915 - 921 (2007).

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