Name That Tune: A Look at the Neural Basis of Tone Deafness

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Biology 202

2006 Third Web Paper

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Name That Tune: A Look at the Neural Basis of Tone Deafness

Andrea Goldstein

Music has long been considered a uniquely human concept. In fact, most psychologists agree that music is a universal human instinct. Like any ability, however, there is great variation in people's musical competence. For every brilliant composer or pianist in the world, there are several people we refer to as tone deaf. Far from being simply unable to carry a tune, people with tone deafness (or amusia, as it has been technically named) are unable to discriminate between tones, notice dissonance, or recognize familiar melodies. Such a "disorder" has been found to occur after some sort of brain damage, but in the last decade, a great deal of research has been done in an attempt to discover the cause of congenital amusia, which cannot be pinned to any brain damage, hearing problems, or lack of exposure to music. The findings of this research make a strong argument for the existence of an inborn disorder that impairs musical ability.

According to the extensive research of Dr. Isabelle Peretz of the University of Montreal, amusia is more complicated than the inability to distinguish pitches.(1). An amusic can distinguish between two pitches that are far apart, but cannot tell the difference between intervals smaller than a half step on the Western diatonic scale, while most people can easily distinguish smaller than that. When listening to melodies which have had a single note altered so that it is out of key with the rest of the melody, amusics do not notice a problem. Similarly, amusics find dissonant chords significantly less unpleasant than do people with normal musical abilities. As would be expected of someone who identifies as tone deaf, amusics perform significantly worse at singing and tapping a rhythm along with a melody than do normal people.(2)

The most fascinating aspect of amusia is how incredibly specific to music it is. Because of its close ties to language, it would seem that a musical impairment may be caused by a language impairment, or the other way around. Studies suggest, however, that language and musical ability are independent of one another. People with brain damage in areas critical to language are often still able to sing, despite being unable to communicate through speech.(3) More interestingly, while amusics show deficiencies in their recognition of pitch differences in melodies, they show no impairment in recognizing intonation in speech. For example, amusics who speak tonal languages, such as Chinese, do not report having any difficulty discriminating between words that differ only in their intonation. The linguistic cues inherent in speech make discrimination of meaning much easier for tone deaf people.(4) Without context clues, however, amusics show impairment in interpreting speech in the same way as interpreting melodies. Amusics are also successful most of the time at detecting the mood of a melody, despite their inability to interpret its tonality. Further experiments have shown that amusics are able to recognize the lyrics of a song out of the context of its melody, can identify a speaker based on his or her voice, and can discriminate and identify environmental sounds.(2) It seems that the issue has nothing to do with hearing; it is a processing deficit that happens further along on the neural pathway.(5) In addition, there is no general deficiency of memory or attention with amusics; the disorder is simply very specific to music.(2)

More recent work has been focused on locating the part of the brain that is responsible for amusia. The temporal lobes of the brain, which are home to the primary auditory cortex (6) have been the primary suspects. It has long been believed that the temporal lobes, especially the right temporal lobe, are most active when engaged in musical activity (3), so any musical disability should logically stem from here as well. Because it has been shown that there is no hearing deficit in amusia, researchers moved on to the temporal neocortex, which is where more sophisticated processing of musical cues was thought to take place. The most recent studies, however, have suggested that the deficits in amusics are located outside the auditory cortex. EEGs of the brains of amusics do not show any reaction at all to differences smaller than a half step. When changes in tones are large, their brains overreact, showing twice as much activity on the right side of the brain as a normal brain hearing the same thing. These differences do not occur in the auditory cortex, indicating again that the deficits of amusia lie not in hearing impairment, but in higher processing of melodies.(5)

So what does this all mean? It depends on your point of view. Looking only at the vast body of research of Peretz and her colleagues in the field of neuropsychology of music, it would appear that there is definitely some sort of disorder at play in amusia. As a student of neurobiology, however, this idea is met with some skepticism. There is no doubt that the studies by Peretz et al. are legitimate and have found significant differences between the brains of so-called amusics and normal brains. The more important question now becomes one of normality. Every trait from skin color to intelligence to mood exists on a continuum – there is a great deal of variation from one extreme to the other. Just because we recognize basic musical ability as something that the vast majority of people have doesn't mean that the lack of it is abnormal. Although our culture has set a cut-off point for many traits (like intelligence or mood), these are arbitrary distinctions between normal and abnormal.

What makes an amusic worse off than a musical prodigy? Musical ability is culturally valued, and may have been a factor in survival at one point in human history, but it does not seem likely that it is being selected for on an evolutionary scale any longer. Darwin believed that music was adaptive as a way of finding a mate (3) , but who needs to be able to sing to find a partner in an age when it's possible to stand outside someone's window playing a song that expresses your emotions on your iPod?

While idea of amusia is interesting, it seems unfounded beyond the interpretation that it is simply one end of the continuum of innate musical ability. Comparing this "disorder" to learning disorders like dyslexia or specific language impairment seems to be going too far in our modern "a diagnosis for everything" society. Before amusia can really be declared a disability, further research must be done to determine whether lack of musical ability is actually detrimental in any way. If no disadvantages can be found to having amusia, then it is no more a disability than having poor fashion sense or bad handwriting.

1)Music on the Brain, from Time Magazine

2) Ayotte, J., Peretz, I., & Hyde, K. "Congenital amusia: A group study of adults afflicted with a music-specific disorder." Brain, 125(2), 238-251.

3)Music of the Hemispheres, from Discover

4)Tonal Languages for the Deaf, from WonderQuest

5)Experts tune in on tone deafness, from BBC News

6)Tonal Hearing, from Instituto de Fisiología Celular

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