How would your life be affected if you could not hear musical pitch properly? For speakers of tonal languages such as Cantonese, not only music appreciation but also language tone processing becomes difficult. Recently, Dr Zhang Cai-cai from the Department of Chinese and Bilingual Studies has investigated congenital amusia among Cantonese speakers and shared some important results.
What is congenital amusia and how does it affect the brains of tonal and non-tonal language speakers differently?
Congenital amusia is a neurodevelopment disorder that hampers the fine-grained processing of musical pitch. In speakers of non-tonal languages, who have been subjected to numerous studies, it occurs due to deficits in the music-selective neural circuitry in the right inferior frontal gyrus of the brain. That has a mild effect on language pitch perception, as pitch is not critical in such languages.
But pitch processing in tonal languages such as Cantonese is far more linguistically important because pitch distinguishes word meanings, so speakers of such languages are more heavily affected by the disease. We focused on Cantonese speakers because the language has three level tones at various pitch heights, which can be precisely matched with musical notes.
How did you find the neural dysfunction affecting Cantonese speaking amusics?
My team used functional magnetic resonance imagining (fMRI) to determine the parts of the brain affected by amusia when participants listened to both piano and Cantonese pitch samples. We found significant activation of the right superior temporal gyrus in musically intact participants when listening to Cantonese words with tone differences, and significant activation again in the cerebellum when listening to both Cantonese words and piano tones. Very differently, amusics registered no such brain activation, which suggests that they have a dysfunctional mechanism of relative pitch processing in the right superior temporal gyrus and cerebellum.
You also found unusual brain activation in other areas among the amusics. Where, and what are the implications?
Yes, the fMRI showed abnormally strong activation in the right middle frontal gyrus and the right precuneus of the amusics in response to both the language and musical pitch stimuli. We think that this probably reflects deficits in working memory or attention when amusics are subjected to repeated pitch stimuli. Taken together with our findings on the dysnfunctional mechanism, these results could help clinicians better fashion interventions for amusia sufferers.