What can tone deafness tell us?

Many of us can't sing very well, and we don't need Simon Cowell to tell us. We mouthed our way through school chorus and the singing parts of religious services. Even now, we belt it out only in the shower or in the car -- alone, with the windows closed. We consider ourselves tone deaf, and we have plenty of company: About one in seven people count themselves among the tone deaf.

But are we? Being tone deaf tends to be equated with an inability to sing, yet there are plenty of terrible singers who hear music just fine and enjoy listening to it. If the term is used in a stricter -- and more literal -- sense to mean people who can't perceive music, the numbers get smaller.

Using music listening tests, researchers have found that only one in 20 people is truly tone deaf. The main deficit for such people is an inability to hear differences in pitch -- how high or low notes are -- so following even the simplest melody is hard work, if not impossible.

In research circles, serious tone deafness is referred to as amusia. If someone is born that way, it's called congenital amusia. Both Milton Friedman and Che Guevara are thought to have had congenital amusia, which, if true, might be the only thing they had in common.

There's been a boomlet in amusia research. Researchers at the University of Montreal developed a series of tests, called the Montreal Battery for the Evaluation of Amusia, which makes it possible to tease apart different types of musical deficits. And sophisticated imaging tests are letting researchers compare the brains of amusics against people with normal musical abilities.

Much of this research is motivated by simple curiosity about how the brain works and the nature of music. As far as we know, no one is working on a cure for tone deafness. But the scientists involved in the research say that amusia may serve as an important model for other developmental disabilities and that by unlocking its mysteries, they'll make discoveries about problems such as learning disabilities.

Pitch problems

Western music is organized into semitones, or half steps, such as the difference between F and F-sharp or between B and B-flat. Most people have no problems distinguishing semitones; in fact, most of us can distinguish between notes that are separated by a fraction of a semitone.

But people with amusia often need a much larger spread before they can reliably hear a difference in pitch. In many cases, the difference must be close to an octave -- which, for example, is the distance between the first two notes of "Over the Rainbow," the famous song from "The Wizard of Oz."

It's not simply pitch in isolation that amusics have difficulty with. They don't hear pitch direction or pitch contour -- the various ups and downs that form a melody -- very well. Experiments have shown that amusics have an especially difficult time picking out pitch changes in the context of a musical phrase.

Some people with amusia seem just as clueless about rhythm as about pitch and melody. If you saw the movie "Motorcycle Diaries" about Che Guevara, you may remember the scene when he dances a tango while everyone else is doing a mambo. Yet several experiments have shown that amusics have a pretty good sense of rhythm if the music played is monotone. It's very possible that when people with amusia listen to a normal piece of music, the pitch changes throw them off, so they also stumble on the music's rhythm.

Bad connection?

There does seem to be an inherited component to being tone deaf. In a study that's often cited, researchers examined the music perception of identical and fraternal twins using the "distorted tunes" test, which preceded the Montreal tests. The identical twins were more likely to have similar test scores. Using standard statistical techniques for twin studies, the researchers estimated that musical listening ability is 70 percent to 80 percent heritable.

In general, music seems to be handled by the right side of the brain. Brain scans haven't revealed any major anatomical differences in people who are tone deaf. It has taken more sophisticated tests to uncover some subtle variations.

An imaging and statistical technique called voxel-based morphometry calculates the density of brain tissue. In a study comparing amusics to people with normal musical ability, researchers used it to measure the white matter (which consists of connecting nerve fibers) between the right frontal lobe, where higher thinking occurs, and the right temporal lobes, where basic processing of sound occurs. The white matter of the amusics was thinner, which suggests a weaker connection. Moreover, the worse the amusia, the thinner the white matter.

This finding is consistent with the notion that our brains use a "distributed network" when we listen to music. There may, indeed, be some sort of "pitch center" in the temporal lobe where the simplest properties of pitch are recognized and processed. But once you add in melody, chords (several pitches played at the same time), counterpoint, scales, and other "rules" of music, more brain power is needed, so the frontal lobes are recruited.

Rhythm and movement are closely related, and several studies show that the cerebellum, the part of the brain that integrates sensory perceptions and movement, may be activated by rhythm. Of course, music often provokes a strong emotional response, so the parts of the brain that cause emotions also join the orchestra.

In one experiment, music that produced "chills" caused more blood flow in reward-seeking areas of the brain -- the same areas that "light up" in response to food, sex, and recreational drugs. This finding could be an argument for or against rock 'n' roll, depending on your point of view.

It's an open question how specialized music processing is. Some experts believe there's a great deal of overlap between music and speech -- which also has elements of pitch and rhythm -- and how the brain handles them. In their view, we're merely harnessing our considerable talents for sound and language when we listen to music.

Others believe that musical perception and thinking happen quite separately from other functions, and our brains are predisposed toward developing centers and networks dedicated exclusively to the job. They cite case reports of brain injuries that robbed people of language but left their musical abilities intact. Of course, people with amusia have the opposite problem: Their language processing seems fine, but music is Greek to them. The existence of amusia when other perceptions and abilities are normal is more evidence that music processing is autonomous.

When people with amusia have been tested on their ability to discriminate between sentences that differed in intonation, they've done just as well as controls. But when words are replaced by notes following the same variations in pitch, they get confused. Researchers believe that spoken speech may be full of stress and timing differences that allow amusics to understand it.

Are you tone deaf?

Researchers at the University of Newcastle-upon-Tyne in England have made available two online tests of musical listening at www.delosis.com/listening.

They're based on the tests developed at the University of Montreal. Each consists of 30 pairs of tunes. You listen to each pair and indicate whether they were the same or different. The idea is to test your ability to identify small differences in melody and rhythm.

The Web site says it takes about eight minutes to take each test, but in our experience it took longer. It was surprisingly difficult to concentrate after a while, and you need to take both tests in order to learn your score.

About 100,000 people have taken the first of the two tests, and the average score is about 25 -- that is, people were typically wrong in about five of the 30 pairs. An editor with a bad singing voice scored 24 (six pairs misidentified) on the first test and 22 on the second, which was proof enough to him that while he is below the mean, he is not quite in the Milton Friedman-Che Guevara category, despite his woeful warbling.