Biology 202

2006 Third Web Paper

On Serendip

I'm sure we all know someone who can't "carry a tune." There is always that one person who you are singing with who just can't seem to hit the right notes. For some of us, this ability comes naturally and does not require particular effort or specific training. I have noticed this and wondered about it my whole life, so when this topic was brought up in class, I wondered what neural mechanisms were involved in this skill and why some people have such problems. In researching this question, I also became interested in whether this ability can be or needs to be taught, and what this tone deafness tells us about how the brain processes music.

Some refer to tone deafness as amusia, but tone deafness is actually a type of amusia, which actually means the inability to comprehend or produce music at all. Tone deafness (otherwise known as tune deafness, dysmelodia or dysmusia) is when an individual can not differentiate between two different notes (it will be referred to as amusia in this paper). In common usage, though, many people say someone is "tone deaf" when they cannot reproduce a particular note—like the earlier example of someone singing (1). Some believe that this inability to produce a tone is more due to a lack of training than is the inability to differentiate tones (1). This brings up an interesting question of whether different systems are involved in each process (differentiating or producing), how one can be deficient while the other is normal, and which is more apt to improve with training.

Amusia can be congenital or caused by an injury later in life, and is estimated to be an affliction of 4% of the population. Some researchers argue that amusia is most often from brain damage or ear damage acquired later in life (6). Regardless, these individuals have normal intellectual, memory, hearing, cognitive and language abilities (2)(3). These individuals also do not show problems with perceiving or reproducing rhythm, showing that this deficit is very specific to pitch processing. Because of the intonation involved in language production and processing, one would think that understanding speech would also be a problem in these individuals, but this is not true (4). Some researchers believe that the perceptual needs for understanding language are much less fine-tuned than those necessary for pitch perception in music, so that the abnormalities these amusic individuals have are not severe enough for them to show deficient language processing (4). Therefore since the deficit is specific to music (and not language or timing) then there must be neural systems devoted specifically to music or at least neural systems devoted to pitch processing that are not involved in rhythm processing or language (at least to the same extent).

Since amusic individuals can be so specifically impaired in differentiating tones, many believe that there must be music-specific neural networks involved in the process (4). This brings up a more general question of how specialized the nervous system is, or how many processes use the same neural connections or systems. One would think that the nervous system would only be hard-wired specifically for certain purposes that are crucial to its survival. Because many argue that music serves no obvious purpose in our species' survival, one would not expect a neural system to be devoted to it alone. Therefore, pitch perception must be carried out in the neural systems that are in place for other functions like language, only at different levels of complexity (4). In other words, some researchers believe that "humans are born with musical predispositions that develop spontaneously into sophisticated knowledge bases and procedures that are unique to music" (4). So the musical predispositions present are actually remnants from other processing but can be developed to be used for musical skills. Other evidence for music-specific neural networks comes from the finding that a focal lesion in the left superior temporal gyrus caused amusia in one case study, where the individual could not recognize or produce melodies, but had no problems with rhythm or speech (7). While it is tempting to conclude that the left superior temporal gyrus is the site for tone deafness, it is still possible that a lesion to another region of the brain could lead to the same result.

On the other hand, there is evidence that music processing and other functions such as language are closely related, and thus might share neural systems. For example, in tonal languages such as Cantonese and Vietnamese, where the tones used to pronounce words can change their meaning, there are almost no tone deaf individuals (1). This suggests that in a culture where differentiating tone is essential to daily life, either these individuals differ genetically in terms of the skills they are capable of, or the skill is hard-wired in all individuals world-wide, and when it is necessary for daily life at a young age and throughout life it is maintained and not allowed to disappear. In countries with non-tonal languages such as the US, and in households where music is not practiced at a very young age, it is possible that this skill is not developed when individuals were born with the possibility to have the skill. Other support for the connection between pitch recognition and other skills is the claim that some researchers make that those with amusia are more likely than most people to have rhythmic and memory/recognition problems (1). Some say that musical ability is made up of many different skills ("neurally isolable processing components") which can be specialized for music (5).

A similar question is whether or not the ability to discriminate notes or reproduce them is innate. In a test where four notes are presented followed by a fifth which is either higher or lower, babies are able to tell the difference in the fifth note, while adults with amusia cannot (4). It would be interesting to study whether babies who later develop amusia are able to detect the difference in tone, since if they were it would mean that every baby is born with this ability and it was just not developed or maintained. But regardless, the vast majority of humans are born with the ability to discriminate different tones, without needing any experience to do so, suggesting that this ability has some sort of universal utility. This five tone test is a new method for measuring tone deafness which is the first to test it reliably (6). Researchers now do not have to rely on subjects to tell them whether they could tell the tones apart or not. By using an electroencephalogram (EEG)—scientists can tell by a subject's brain waves whether or not they detected the change in the fifth tone. There is a spike of electrical activity mainly from the right hemisphere, starting 200 ms after the tone, which signals a change in pitch in normal individuals and which is not present in individuals with amusia (2). Therefore, the amusic individuals' brains are not registering the difference.

Some researchers claim that training can improve tone deafness (some say completely), while others say that training is only effective in young children (and others say it is untreatable whatsoever) (2). It is unclear why there would be differences in training responsiveness between pitch discrimination, pitch reproduction or matching a tone, since matching a tone in fact requires the discrimination between the tone you are producing and the one you are trying to match. Pitch recognition involves comparing sensory input to either long-term or short-term memory, while matching a sung note with an outside note involves a feedback loop—such that an individual compares the sensory input coming from their own voice, and compares it with the other consecutive sensory input of the true tone. Therefore, if the feedback loop is damaged, one would not be able to tell that there was a difference between the tone you were producing and the reference tone (identical to how those with amusia cannot differentiate between two different tones). However, it is unclear how those without amusia, who can tell apart notes in melodies, still cannot match a note. Therefore, they can discriminate between two notes in a task but not between the note they are producing and the reference tone, and cannot/do not alter their tone to match them.

As I was researching amusia I became interested in how so many of us can distinguish tones and match tones so effortlessly. This is remarkable since in order to determine the tone being heard, the ear and brain must extract the pure tone since different instruments add different oscillations over the pure tones. And after the pure tone is extracted, it must be accurately compared to the previous tone in short-term memory. One remarkable phenomenon on the other end of the continuum from tone deafness is those individuals who are able to produce a certain pitch without hearing an initial reference tone. This is called perfect pitch, or absolute pitch, and is present in about 1 in every 10,000 people in America (9). It has been seen in as many as 1 in every 20 people in other countries (9). These individuals with perfect pitch are also able to recognize pitches instantly and with no effortful processing, and with no external reference pitch (8). Anecdotally, some individuals say that they compare the note to an internal reference pitch while others just report knowing the pitch intuitively (8).

Again, there are opposing theories on the genetic and environmental contributions to this ability, as some believe we all were born with perfect pitch (and either do or do not develop the skill depending on our experience), and others believe certain individuals are predisposed to have the talent (9). There is some evidence that certain groups, including autistic individuals, have an especially large incidence of perfect pitch (around 1 in 20 individuals), suggesting that there is a strong genetic influence on this ability (9). It is very easy to find materials online which claim to be able to teach adults how to obtain perfect pitch, showing that a large group of people believe that this is a teachable skill, even late in adulthood (10).

So what has all this taught us? Initially I believed that being able to sing "on key" was an ability you were either born with or without, but there is convincing evidence showing that certain experiences in early life might play a role in developing these abilities—the potential for which we might all be born with. Therefore, your friend who cannot match that note on the radio might have just not needed the skill enough in early life for it to remain or become developed. However, the differences are not entirely due to experience, since the evidence for genetic variation is also pretty convincing, since certain cultures and certain disorders show dramatically different amounts of tone deafness and perfect pitch than others. It also seems very likely that these deficits or exceptional abilities are localized to neural processes which can be developed specifically for music, since deficits in timing and language are not often seen in tone deaf individuals, and lesions to a specific part of the brain can cause tone deafness without the related deficits. It is possible that there are differences in the neural processes involved in producing and differentiating tones, but it is not clear why since both involve differentiating. Regardless, there is some evidence that pitch recognition, even perfect pitch, can be affected by experience, and thus can be taught late into adulthood.

1)Wikipedia tone deaf site, a good description of tone deafness on Wikipedia
2)EEG study, an article on the EEGs of tone deaf individuals
3)amusic study, an abstract of a study on amusic individuals
4)amusia study, an article describing amusia and the five tone task
5)music processing, an article on music processing
6)NPR article, an article on tone deafness for a general audience
7)lesion study, a lesion case study causing amusia
8)perfect pitch, a website on perfect pitch
9)wikipedia, a broad description of perfect pitch
10)perfect pitch training, a site advertising a perfect pitch training program


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