What causes tone deafness?

Tone Deafness and Your Nerves

So, what's the reason for the wounded warbles that are emitted from a tone-deaf singer's mouth? Why can't they distinguish pitch?

The brain is still quite mysterious to us, but we know it has a very adaptable nature. People seem to have a range of ability within a given skill set, and their ability can float within that range depending on frequency of exposure or practice. A person with poor pitch perception may be able to improve his or her ability to differentiate pitches or mimic them, but a person who is truly tone deaf may not have the capacity to improve whatsoever no matter how much he or she practices.

The level of exposure to music as a child may play a part, in that the brain may have reduced capacity for pitch mimicry. But this -- nor any other environmental factor -- doesn't account for tone deafness.

Tone deafness seems to be entirely hereditary, and identical twins score similarly when taking pitch tests [source: Barrie]. As we mentioned earlier, it's not the reception of the tone that is compromised, but the brain's processing of it.

And though there is still a great deal to learn about the brain, advancing technologies are providing us better glimpses of how communication occurs between regions of the brain. Researchers have used MRI-like scanning techniques to examine a portion of the brain -- the arcuate fasciculus -- that is a bundle of nerves that delivers information from one part of the brain to another.

While there may be other functions occurring, one of the known roles of the arcuate fasciculus is to relay signals concerning the perception of sound to parts of the brain related to reproducing that sound. In tone-deaf people, however, these nerve fibers were much smaller than normal [source: Society for Neuroscience]. One particular branch of the arcuate fasciculus couldn't be found at all in the tone-deaf subjects.

This band of nerves also seems related to the ability to repeat verbatim a sentence that has been spoken by another person. This condition, conduction aphasia, is entirely separate from tone deafness, but seems to be caused by a similar disruption or diminishment of the arcuate fasciculus [source: Bernal]. So if you tell a tone-deaf person "nice singing" after they've left the karaoke stage, don't do it too snarkily: Tone-deaf people can detect sarcasm and other tonal variations in the human voice.

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