/sci/ - Science & Math

When you dream, what are you actually 'seeing' with? Obviously your eyes are shut, so where do these images display? I mean I can think about an apple, but I can't really see it as clearly as I could when I"m dreaming. So when you sleep, is there a sort of 'mind's eye' that opens up? Also as a side note, has anyone found out why we dream? Whats the point of it, and does it have any function?