Sound perception and tone deafness

This week’s topic was the auditory system in the brain, starting from the anatomy of the ear, ending with sound perception. Since valuable information of systems – especially in the brain – is often acquired by investigating disruptions and diseases in the system, it is quite natural to start thinking about disturbances in sound perception. Music has always been a big part of my life, and thus I find it interesting how it is possible that some people cannot distinguish notes from each other. Moreover, some people seem to be able to learn this skill, if they put in time and effort, while others seem to be incapable of this.

It is, indeed, the case that most people are able to learn to improve at pitch discrimination and singing in tune. In this case, there is no apparent impairment in the brain structure, but these kinds of skills, of course, require some training. Intuitively, the auditory system seems much simpler than the olfactory system, for example, because there are far less tones than there are smells. Yet for some people, learning pitch discrimination seems to require a huge amount of effort, while for others it is completely effortless.

The “real” tone-deafness is called amusia, which can be “acquired” as a result of brain damage or it can be innate, in which case it is called congenital amusia. About 4% of the population suffers from congenital amusia, where fine-grained pitch discrimination does not function properly. Different types of amusia may combine dissociations in of the elements of music processing: rhythm, melody and emotional associations. People with congenital amusia cannot recognize dissonant chords, whereas most newborns already possess this ability. In addition, they are more likely to also lack a sense of rhythm.

It seems that there are many ways by which amusia could result. In EEG experiments, it has been often observed that compared to “normal brains”, amusic brains lack auditory communication to higher brain areas. Structural neuroimaging experiments support this conclusion, as people with congenital amusia have weaker connections between frontal areas and posterior auditory areas. Therefore, the problem lies in perceiving the pitch, not in the brain detecting the notes. Based on “acquired amusia” brains, a few areas have been reported to have a connection to it. In addition to the primary and secondary auditory cortices, these include reduced white matter concentration in the right inferior frontal gyrus and the absence of the superior arcuate fasciculus.

Sound perception seems to be incredibly complex. If someone can be tone deaf, would it be possible that to some people, harmonious chords sound like they are not in harmony at all, but do not sound like noise? How can we know that our experiences of the chords are similar, in the first place?

Posted by Meo Ekroos

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