Music and Brain Blog at University of Toronto: Tone deaf: Physical deafness, Dyslexia, or is it simply a term used flippantly to describe someone who struggles to distinguish pitch variants?

tone-deaf [tōn-def]

adj. Unable to distinguish differences of musical pitch

Robert Jourdain, author of Music, the Brain, and Ecstasy writes, “for reasons not yet understood, their (monotones, or the tone deaf) measurements across pitch and space are imprecise and unstable.”[1] Well the good news is that since 1997, more research has gone into this topic with a great number of publications on the subject. It is pleasing to know that tone deafness (congenital amusia) has been explored, and classified as a pitch perception and production impairment. As I have come across a great number of people who believed themselves to be tone deaf, only to discover they weren’t (thanks to a little attention being paid to listening particular notes and singing them back), it was great to find that this is a real condition that affects individuals, “estimated to comprise about 4% of the population.”[2] Therefore, it is a term that is used frequently by the public rather flippantly, but it does in fact affect a number of people.

With this in mind, the following essay will examine:

1. How sound is perceived.

2. The structural differences in the brain for amusics.

3. Recognition of tones and sentences.

4. Its relationship to Dyslexia.

What will become evident is that this is not a physical deafness at all, but a lack of ability to perceive pitch. It will also highlight the common thread with dyslexia, showing a correlation between an impairment in phonemic awareness, and the processing of speech intonation. In his book, Jourdain was accurate in his assumptions/predictions of amusia, but it was still hypothetical at that time. Science has progressed further, and the research has become more concise.

Firstly, when vibrating air molecules enter the ear, the sound energy is transmitted to the auditory cortex, where sound information is processed. The auditory cortex is located in the temporal lobe, just forward of the occipital lobe. The point to make here is that congenital amusical individuals process and recognize speech, including speech prosody, common environmental sounds and human voices, they are just impaired when it comes to perception and production. One of the reasons for this is because neural substrates of sound perception and production are connected by the arcuate fasciculus (a fiber tract connecting temporal and frontal brain regions), and in tone-deaf individuals, they “have reduced arcuate fasciculus (AF) connectivity.”[3] Psyche Loui, David Alsop and Gottfried Schlaug used structural MRI with diffusion tensor imaging to reconstruct white matter tracts. What they found was that both the superior and inferior AF were reliably identifiable in normal subjects (those who are not tone-deaf), whereas “only the inferior AF was identifiable bilaterally in all tone-deaf individuals.”[4] Meaning, the white matter (connecting nerve fibers) between the frontal lobe and the temporal lobes in amusics was thinner, which suggests this weaker connection.

However, do the perception deficits in musical tones cross over, or share similar problems with language? Recent studies would seem to suggest they do. There are two types of sentences one will hear - either a statement, or a question. In both, the intonation contour differs at the end of a phrase with a rising or falling pitch glide. A question has a slight raise in pitch at the end while a statement will dip down. It has been stated that amusics have difficulty in discriminating tone sequence analogs of statements and questions.[5] This is because in general, small interval changes are unrecognizable to tone-deaf patients. Only when intervals are large enough may the information be processed.

Knowing the correlation between music and language, perhaps it is for this reason that researchers have explored the relationship between amusia and dyslexia? Tone-deafness is a pitch related impairment, and dyslexia is a lack of phonemic awareness. Recent studies have “demonstrated significant relationships between phonemic awareness and musical sound processing in children as well as adults,”[6] based on the fact that different consonants and vowels are characterized by different frequencies. This is an interesting concept, which I have had to think about. I knew someone who was dyslexic, but was a fantastic singer who represented her country with the National Youth Choir of New Zealand. From what I could see, her dyslexia had no bearing on her ability to process, and then produce pleasing music. However, on the other side of the scale, my sister, who is also dyslexic, did have issues in matching pitch. She worked hard at it, but it was not easy for her. I would suggest that perhaps my colleague from New Zealand, while dyslexic, had full AF connectivity, represented in non-tone-deaf persons, whereas in my sister, her nerve fibers between the frontal lobe and the temporal lobes would be thinner, reducing this AF connectivity. Being made aware that there is possibly a connection between the two makes complete sense. However, we still have to notice that the research of Loui, Kroog, Zuk, Winner and Schlaug reveal only a partial correlation. Further research would need to be done.

Therefore, the results presented show a further development in understanding amusia. It is now known that those who suffer from amusia have “demonstrated a deficit in the perception in music.”[7] Where music can provide a pleasurable experience, some tone-deaf patients describe music as unpleasant. Because the structure of the musical sentence (pitch-pattern analysis) cannot be distinguished, it can be heard a just a big onslaught of noise. Knowing that tone-deafness is not an issue of ‘hearing’ (amusics are not physically deaf), but of a neurological deficit, we can see that this is a real disorder for some. While the term is often misused, it is simply not a term used flippantly to describe someone who struggles to distinguish pitch variants.

[1] Jourdain, Robert. Music, the Brain, and Ecstasy: How Music Captures Our Imagination. p.113

[2] Patel, Aniruddh D; Wong, Meredith; Foxton, Jessica; Lochy, Aliette; Peretz, Isabelle. “Speech Intonation Perception Deficits in Musical Tone Deafness (Congenital Amusia)” p.357

[3] Loui, Psyche; Alsop, David; Schlaug, Gottfried. “Tone Deafness: A New Disconnection Syndrome?” p.10215

[4] Loui, Psyche; Alsop, David; Schlaug, Gottfried. “Tone Deafness: A New Disconnection Syndrome?” p.10216

[5] Patel, Aniruddh D; Wong, Meredith; Foxton, Jessica; Lochy, Aliette; Peretz, Isabelle. “Speech Intonation Perception Deficits in Musical Tone Deafness (Congenital Amusia)” p.358

[6] Loui, Psyche; Kroog, Kenneth; Zuk, Jennifer; Winner, Ellen; Schlaug, Gottfried. “Relating pitch awareness to phonemic awareness in children: implications for tone-deafness and dyslexia.” p.1

[7] Griffiths, Timothy D. “Tone deafness: a model complex cortical phenotype.” p.592

Bibliography/References:

Foxton, Jessica M; Dean, Jennifer L; Gee, Rosemary; Peretz, Isabelle and Griffiths, Timothy D. “Characterization of deficits in pitch perception underlying `tone deafness'.” Brain, Volume 127, Number 4 (February 2004): pp.801-810

Griffiths, Timothy D. “Tone deafness: a model complex cortical phenotype.” Clinical Medicine Volume

8, Number 6

(Dec 2008): pp.592-595.

Jourdain, Robert. Music, the Brain, and Ecstasy: How Music Captures Our Imagination. New York: HarperCollins Publishers, 1997

Loui, Psyche; Alsop, David; Schlaug, Gottfried. “Tone Deafness: A New Disconnection Syndrome?” The Journal of Neuroscience, 29(33) (August 2009 ): pp.10215–10220

Loui, Psyche; Kroog, Kenneth; Zuk, Jennifer; Winner, Ellen; Schlaug, Gottfried. “Relating pitch awareness to phonemic awareness in children: implications for tone-deafness and dyslexia.” Frontiers in Psychology, Volume 2, Article 111 (May 2011): pp.1-5.

Loui, Psyche; Schlaug, Gottfried. “Impaired learning of event frequencies in tone deafness.” Annals of the New York Academy of Sciences, 1252 (April 2012): pp.354-360.