People who are tone deaf -- unable to hear differences in pitch and tone -- aren't just awful singers. At the most extreme, they're unable to perceive music, period. As Oliver Sacks, purveyor of all things strange in the brain, put it in his 2007 book Musicophilia, "Without these basic building blocks [of pitch and tone], there can be no sense of a tonal center or key, no sense of scale or melody or harmony -- and more than, in a spoken language, one can have words without syllables." And as a new study out last week showed, they have actual differences in brain structure from people for whom musical comes naturally.
The tone deaf have, as one of the first empirical studies of the condition defined it, a learning disability. Isabelle Peretz, a cognitive neuropsychologist, and her team at the University of Montreal reasoned that most children learn to sing just as they learn to speak -- seemingly automatically, and without formal instruction. Tone deaf children do not. Peretz gave the disorder the official name "congenital amusia." "Congenital" because it's innate: the brains of people with the disorder never developed the ability to process pitch. Amusia refers to that absence of musical perception. It's also, as Peretz later determined by studying amusica families, to some degree hereditary.
In the little more than a decade since tone deafness was first understood to be a disorder -- "not a myth but a genuine learning disability for music" -- researchers have been trying to figure out how it happens, and if there's anything to be done about it. The approximately four percent of the population with amusia, Peretz established, have usually grown up with normal exposure to music, and can be otherwise intelligent and well-educated. One early case she describes was a man reported by his piano teacher for his inability to sing, to tell the difference between two pitches, and to keep time. At the same time, Peretz notes, "this same subject could speak three foreign languages fluently."
In that first study, her team identified 11 adults who seemed likely to have truly amusia and subjected them to six tests that judged their perception of the melodic and temporal aspects of music, along with their musical memory (their ability to recognize songs). Her subjects all performed at least three standard deviations below the mean on at least two of the tests. That inability to recognize pitch, moreover, only applied to music -- not language. When the melody and lyrics of popular songs were presented separately, the amusic participants were generally able to recognize spoken lyrics, but were significantly impaired in their ability to tell whether they had heard a tune before.
It's been difficult for researchers to get over the idea that, with enough exposure to music, people born with amusia might somehow learn to listen. But even as music has become even more pervasive (think iPods), the condition persists. Last year, Peretz and her team looked into the potential to train young people with amusia, who they reasoned might have enough brain plasticity to be somewhat remediated. They gave 14 amusic 10- to 13-year-olds their basic test for music-hearing ability, then sent them home with MP3 players loaded with popular music (200 songs they found on the Internet, such as "No One" by Alicia Keys), which they were instructed to listen to for 30 minutes a day. Four weeks later, they were retested.