Ahhhh hearing things like that makes me think of all the practice and frustration that must have gone into it... yikes. But this is true... it doesn't have to even be that complicated-- even an etude (like Chopin's in C sharp minor comes to mind as a perfect example) helps with that coordination, because you switch back and forth between what the left hand does and the right hand, so much. Like it's impossible to do that (or to do it fast and right, at least) if you're not used to using both equally. And if you're not used to it, you get used to it after a few hours of practice. By the way, JM, off topic, I'm curious... at what age did you start playing the piano?

And no, the voices in your head are not a bad thing; I think of them as my friends.