In My Mind's Ear

I was talking with a friend today who told me to "listen to something with my mind's eye." This made me wonder whether or not there is such a thing as a 'mind's ear'. Upon further discussion an reflection, we concluded that there must be a 'mind's ear', at least metaphorically, because otherwise it could never get too loud to hear yourself think. Now, I like working out kinks in common metaphors as much as the next person, but this conclusion of ours lead to another, more complicated question: How can there be a listener (the mind's ear) and a speaker (the self) within a single (sane) mind, what areas of the self/cognition are responsible for hearing and speaking, and how is all this synthesized into a cohesive whole? These are essentially questions that lie at the heart of Cognitive Science. Any thoughts on the subject?