Yeah, you can definitely influence your perception. I was talking with my roommate about perception and we agreed that sensation is the stuff that enters your mind from the outside. Perception is what happens when it commingles with your memory/associations. So I might see an object moving (sensation) but when it "enters" my mind, it gets associates with bird, and all the stuff "bird" does, and there might be some idea about it's purpose and intention, etc.
The sensation component is pretty constant while the resulting perception is very fungible, since it's dependent on the ideas and associations you invoke, consciously or subconsciously. When you use drugs, you influence some of those associations, either by suspending them, or making them conscious so you can see that they are just associations and not objects themselves.
Does it bear some relationship to functions? I don't really care. (Not to sound mean, I just don't think it matters and just leads to confusion.)