This may come as a shock to anyone who has listened to pop music recently but true tone deafness, or amusia, as it is known to medical experts, is rare.

Researchers have found that only 1 in 20 people truly have amusia. Tests have shown that many people who cannot sing hear music just fine. They just cannot sing.

True amusics cannot pick out differences in pitch or follow the simplest tunes, reports the September 2007 issue of the Harvard Health Letter.

Amusia is easy to identify, but not so easy to explain. Brain scans have not shown significant anatomical differences in people with amusia but more sophisticated tests have uncovered some subtle variations. In a study comparing amusics to people with normal musical ability, researchers used brain imaging to measure the density of the white matter between the right frontal lobe, where higher thinking occurs, and the right temporal lobes, where basic processing of sound occurs. The white matter of the amusics was thinner, which may mean a weaker connection. And the worse the tone deafness, the thinner the white matter was.

Some experts believe that there is a lot of overlap between how the brain handles music and how it handles speech; both depend on pitch and rhythm. Others believe that musical perception and thinking occur separately from other functions, and that our brains develop networks that are used only for music.

If you want to test your ability to perceive music, researchers at the University of Newcastle-upon-Tyne in England have developed a fun online test at