Why Doesn't Miley Cyrus Sound Like a Hick When She Sings?

I just saw Miley Cyrus speak for the first time this week on SNL and Fallon, and I had no idea that her normal speaking voice was so...

...lets not pull punches - she sounds like a hick.

Where the hell does her accent go when she starts singing?  Lets not blame the obvious here - Autotune.  This is a phenomenon I've heard with other singers, particularly British/Scottish/Irish where their thick natural accent is completely lost when they start to sing.

Other times, its plain as day, such as with the Cranberries, or Little Talks, or George Strait.

What's going on?

There are two interesting explanations for this phenomenon.

The first starts by looking at what we talk about when discuss speech accents.  In particular, the tone, meter, altered phonics, syllabic emphasis, and even vocabulary all go into what we consider an "accent".  It also turns out that when you sing, pretty much all of this is overwritten by the song.

So, if the song isn't written for an accent, it usually disappears because the constructed nature of singing a song removes the inclination to turn words into your natural sounding speaking voice.

The other explanation is more physiological.

Basically, the parts of the brain that control speech are not the same that control singing.  On interesting effect of this is that people with a speech impediment (such as stuttering) can lose this impediment completely when singing.