I'm wondering if someone can clear up a related question. I've always heard that two ears are needed to identify the direction of sound. However, I can tell the direction of a sound when one ear is covered up and without moving my head. Try it yourself: put a TV or other sound source behind yourself, positioned a little to the left or right, cover one ear, and you'll see that you can reliably tell whether it's more left or more right. So I think that something more complicated is going on within the ear and that a single ear is not strictly unidirectional.