Patient Matthieu Dion - his real name - is famous for being the first person ever diagnosed with beat deafness.
You read that correctly. Beat deafness.
He cannot “hear” rhythms - defined as “the pattern of time intervals in a sequence … often perceived in the context of a musical beat.” He once said in an interview “I just can’t figure out what’s rhythm … I just can’t hear it, or I just can’t feel it.”
His body is affected as well as his mind. Matthieu cannot clap along with a beat and he can’t move to a beat and, of course, he can’t dance. These would require motor skills necessary to synch his body with auditory information.
He also has difficulties with meter. You might recall that meter is a repetitive pattern of strong and weak beats, involving the ability to perceive their subdivisions. Matthieu cannot distinguish 4/4 time, (often called “common time”) from 3/4 time (which is what most waltzes are made of). If his brain perceives incoming audio as music, Matthieu lives in a beatless, meterless world.
Here’s the weird thing. If you drop pitch and harmony, everything changes. Mathieu can readily hear timed beats that are NOT fundamentally musical in nature, like a metronome, or a grandfather clock, these deficits disappear. His body can even respond with synchronized movement - as long as there is no musical context in which the beats are experienced.
We’ve come a long way in our understanding of beat deafness since 2011, the year Matthieu was first described. It affects about 3% of the population, and often occurs in people co-diagnosed with dyslexia.
THE STRUCTURE OF THE MUSICAL MODULE.
Here’s a confounder: Unlike Monica or Florence Foster Jenkins or any of the other subjects we’ve previously mentioned, Matthieu could carry a tune. His pitch discrimination and pitch perceptions were proficient.
Such remarkably specific deficits have allowed us to characterize some of rhythm’s neuroanatomical substrates. We now know beats are processed in at least three domains, several involving motor movement. It may be one of the reasons why you want to move when you “hear the groove.” One region of that “groove box” is nested in the cerebellum, for example. This region is a highly compressed ball of neurons squatting beneath the main structures of the brain at the back of your head. It’s a big place. If unfolded, this part of your brain would be about 3 feet long, and 4 inches wide.
The cerebellum supervises most motor functions that matter in daily life. Heavily damage it and you’ll have trouble walking or reaching for objects or estimating distances between you and other things. You’ll also have trouble with repetitive auditory information, which, of course, includes beats.
Given data like these, researchers have concluded several things about the brain’s musical module. It appears to be subdivided into two cognitive domains, one processing pitch, the other rhythm. They are at least partially dissociable. That’s why Matthieu could still sing on cue easily. Indeed, he took singing lessons for many years.
But not, as you might predict, drum lessons.
REFERENCES
Phillips-Silver, J. et al "Born to Dance but Beat Deaf: A New Form of Congenital Amusia.". Neuropsychologia 49, no. 5 (2011): 961-69.
Kasdan, A.V. et al "Identifying a Brain Network for Musical Rhythm: A Functional Neuroimaging Meta-Analysis and Systematic Review." Neurosci Biobehave Rev 136 (2022): 104588.
Hawthorn, A. "Why Some People Just Have No Rhythm." Psych Today https://www.psychologytoday.com/us/blog/the-sensory-revolution/202003/dont-got-rhythm-what-it-means-to-be-beat-deaf (2023).