Amusia

There are individuals in whom the mechanisms of hearing function in a way that processing of musical sounds is not possible. This condition is called tone-deafness or amusia

Almost all individuals are equipped with the neural mechanisms needed to make, perceive and enjoy music. In some individuals, these mechanisms are enhanced or respond to training in such a way that exceptional musical skills emerge. At the other end of the spectrum there are individuals in whom the mechanisms function in a way that even normal processing of musical sounds is not possible. This later condition is called tone-deafness or amusia, typically affecting around 4 % of the population.

Amusia entails difficulties in perceiving and producing musical pitch changes. (Although recently, a specific disruption of rhythm, but not pitch processing has been reported. This means that people with amusia can sing off key without realizing it, cannot remember melodies, or tell a major key from a minor one. Individuals with amusia can also have a hard time recognizing songs, even the most familiar ones like “Happy Birthday”. Most (but interestingly, not all) people who fit the criteria for amusia are also poor singers. Amusia can be assessed with a test called the MBEA (Montreal Battery of Evaluation of Amusia) that investigates processing of contour, key, intervals, rhythm, meter, and memory for music. If you think that you may fit the description, a test is available on the website of BRAMS, the International Laboratory for Brain, Music and Sound Research.

Recent studies have started to broaden the picture of the neural basis of amusia and its effects on music listening.

Research typically divides amusia into two types: congenital and acquired. Congenital amusia is a disorder that people are born with, and one that has substantial heritability: according to a study 39% of first-degree relatives have the same disorder. Acquired amusia is not present at birth but emerges due to a specific cause, for instance after a brain lesion that disrupts the functioning of brain areas needed for pitch perception and production. Therefore, in acquired amusia, individuals with previously normal pitch processing experience sudden loss of these skills.

What does a sudden loss of the ability to perceive pitch changes in music feel like? In his book Musicophilia, late Oliver Sacks describes his own experience of amusia, brought on by a migraine attack: “I was driving along the Bronx River Parkway, listening to a Chopin ballade on the radio, when a strange alteration of the music occurred. The beautiful piano tones started to lose their pitch and their character and were reduced, within a couple of minutes, to a sort of toneless banging with an unpleasant metallic reverberation, as if the ballade were being played with a hammer on sheet metal. Though I had lost all sense of melody, I had no impairment of rhythmic sense and I could still recognize the ballade by its rhythmic structure.” This story illustrates perhaps why so many individuals with amusia do not enjoy music - without the ability to perceive pitch changes, music seems to come very close to mere noise.

The description of amusia as a disorder of perceiving pitch changes in music seems quite straightforward. However, recent studies have started to broaden the picture of the neural basis of amusia and its effects on music listening. In a study published very recently, researchers Nathalie Gosselin, Sébastien Paquette and one of the most prominent researchers of amusia, Isabelle Peretz, report interesting findings from two experiments on how individuals with amusia perceive emotions in music.  In the first experiment, individuals with amusia and individuals with normal pitch perception rated to what extent a selected set of musical clips expressed happiness, sadness, fear, or peacefulness. Surprisingly, there were no differences between the participants with and without amusia in the detection of these basic emotions in music. The participants with amusia were significantly worse than control participants in detecting pitch and timing errors in the pieces used in the experiment, indicating that successful emotion recognition didn’t emerge because the pieces used were somehow easier for the amusic individuals to process. (Examples of these errors that individuals with amusia have a hard time recognizing can be heard here.) Therefore, even though amusic individuals have a wide range of difficulties in musical processing and memory, perception of emotions in music may be intact in this population.

Surprisingly, there were no differences between the participants with and without amusia in the detection of these basic emotions in music.

What could then explain successful emotion recognition in music despite severe difficulties in pitch change perception? The second experiment reported in the study by Gosselin and colleagues was conducted to investigate whether tempo. is used by participants with amusia to identify emotions. Participants listened to happy or sad classical music pieces in their original form as well as in two modified forms and rated the emotions conveyed by the music. The researchers modified the mode (from major to usually minor, and vice versa) and the tempo (from fast to slow and vice versa) of the musical pieces. These modulations of tempo affected the ratings of emotions for both control and amusic groups, with faster tempo being associated with happiness and slower tempo with sadness, but modulations of mode affected ratings in only the control group. In summary, individuals with amusia can use information other than pitch, for example tempo, to determine the emotion conveyed by a piece of music. This means that individuals with amusia can also experience emotions while listening to music.

Another recently published study provides insight into brain mechanisms that are at the root of the pitch processing deficit in amusia. In this study by Benjamin Rich Zendel, Marie-Élaine Lagrois, Nicolas Robitaille, and Isabelle Peretz, individuals with and without amusia were asked to respond to clicks or pitch deviations embedded in a melody. The catch was that the pitch deviations were present in both conditions, but participants were asked to attend to them only in one. The brain responses to the pitch deviations in the melodies were measured with EEG. Surprisingly, the brains of individuals with amusia responded to the deviations in pitch similarly to the brains of individuals without amusia, but only in the condition where they were not asked to attend to pitch. Therefore, intriguingly, attending to the pitch information seemed to inhibit the cortical processing of pitch information. This means that the brains of individuals with amusia can process pitch, but this information is for some reason not consciously available. Based on these results, the researchers propose that congenital amusia is predominantly a disorder of top-down mechanisms, where information of pitch changes cannot be attained and used by conscious processes.

Even with advancements in brain imaging, disorders of the brain offer a unique way to investigate brain functioning. Understanding how disturbances in brain function influence cognitive processes helps in piecing together the grand puzzle of how the brain gives rise to the mind. The intriguing cases of congenital and acquired amusia can help scientists understand the fundamental neural basis of music.

written by ketki karanam

 

references:

Peretz, I., Cummings, S., & Dubé, M.-P. (2007). The Genetics of Congenital Amusia (Tone Deafness): A Family-Aggregation Study. The American Journal of Human Genetics, 81(3), 582–588. doi:10.1086/521337

Peretz, I., & Hyde, K. L. (2003). What is specific to music processing? Insights from congenital amusia. Trends in Cognitive Sciences, 7(8), 362–367. doi:10.1016/s1364-6613(03)00150-5

Phillips-Silver, J., Toiviainen, P., Gosselin, N., Piché, O., Nozaradan, S., Palmer, C., & Peretz, I. (2011). Born to dance but beat deaf: A new form of congenital amusia. Neuropsychologia, 49(5), 961–969. doi:10.1016/j.neuropsychologia.2011.02.002

Zendel, B. R., Lagrois, M.-E., Robitaille, N., & Peretz, I. (2015). Attending to Pitch Information Inhibits Processing of Pitch Information: The Curious Case of Amusia. Journal of Neuroscience, 35(9), 3815–3824. doi:10.1523/jneurosci.3766-14.2015