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You probably know someone who says they're tone-deaf. And hey, you might believe it.

I mean, you've heard their off-key version of “Happy Birthday.” And when it comes to karaoke night…Well, you just appreciate their enthusiasm. In reality, though, there's a difference between singing off-key and being truly tone-deaf. Your friend might not be able to carry a tune for all kinds of reasons, but for those with congenital amusia, the situation is pretty simple: Their brains just can't perceive musical pitches.

It seems to happen thanks to specific changes in their brains. And by understanding how it all goes down, scientists are figuring out more about how we process music in general. Maybe unsurprisingly, music is really important to our species.

Like, babies can tell the difference between two melodies before they can even talk. And every culture on Earth has some form of music. Researchers think we may have evolved to love it because it's so useful for bonding with other people.

I mean, who doesn't like a good Karaoke night? So it makes sense that true tone-deafness is pretty rare, no matter how many people might tell you they're tone-deaf. The truth is, congenital amusia probably affects less than 2% of the population.

People with it, also known as amusics, truly can't hear the difference between two pitches. In general, they can't recognize a familiar tune without the lyrics or pick out a wrong note in a song they do know. And you know that cringey sound of dissonance that you hear when two notes clash?

Well, if you do, you probably aren't tone-deaf. For people with congenital amusia, researchers have said that a concert sounds like a foreign speech — just meaningless noise. Fortunately, amusia generally only affects people's perception of music, so they don't have trouble hearing non-musical sounds.

Like, amusic people can still tell people apart by their voices and pick out different noises in their environment. They just can't hear pitch. This disorder affects slightly more women than men, and it's strongly tied to genetics.

For instance, a 2007 study looked at 71 members of 9 families that had at least one amusic person in them. And it found that 39 % of people with amusia also had first-degree relatives with the disorder. Right now, we don't know exactly which genes are responsible for this condition.

But we do know that amusia seems to be connected to differences in the brain. Specifically, differences in a region called the right inferior frontal gyrus. This area may be important for processing and remembering musical pitches.

Scientists are still debating the exact biological root of amusia, but some MRI studies show that people with congenital amusia have less white matter there. White matter helps carry information around the brain. So researchers believe that a lack of it could be a sign of less traffic between key parts of the brain that are involved in hearing music.

But not everyone who's a bad singer has an actual genetic disorder that makes them tone-deaf. Some people can hear pitches fine; they just can't reproduce them. There are all sorts of steps that happen in your brain between when you hear a pitch and when you try to reproduce it — and a disconnect anywhere along the way can throw you off key.

There are a few ideas about where that breakdown might happen. Some research suggests that poor singers just don't have precise control of their larynx, so even though they hear the right pitch correctly, they just can't reproduce it. Other studies have suggested that it's a wiring issue.

Most people hear a note and then their vocal muscles get together and reproduce that same note. But for some people, the mapping might be off — like, every time they hear a B-flat, their brains might map it to the motor pathways that make, say, a C. Then there's even support for the idea that off-key singers just have a bad musical memory — so by the time they're ready to imitate the note they've heard, they've already forgotten it.

There may not be one single answer, because no one explanation describes all poor-pitch singers perfectly. People also respond differently to things like accompaniment and training, which can help some people reproduce a melody — but not everyone. All of this points to the idea that music doesn't target just one place in the brain.

It's a whole network of connected parts, and differences in any given region can alter how you perceive or produce music. In the end, there are plenty of reasons a person might be bad at singing without being tone-deaf. Because singing well relies on many different elements — not just hearing.

And if any one of them fails, well, you might skip the next karaoke night. Thanks for watching this episode of SciShow Psych! And thanks to our patrons for supporting free education on the internet.

We couldn't do this without you. And if you're not a patron but you like what we do here at SciShow, you can learn about supporting us at patreon.com/scishow. [ ♪OUTRO ].