Also, I think rhythmic language (poems with a set meter) and other conventions of versification (end rhymes, assonance, alliteration, metaphor, and the like) act almost the way shamanic drumming does. They help hold the reader (or really, the listener, since all skilled readers of poetry hear the words in their minds) in a state of hightened yet suspended awareness -- like a trance. And that helps the imagination open up.
I seem to recall that W. B. Yeats wrote an essay on this point, published in his collection Ideas of Good and Evil, but I can't remember what the title of the essay is... perhaps: "Speaking to the Psaltry" (?)
Actually, now that I think about it, even "free verse" poems rely on rhythmic language. But the rhythms in free verse shift around from line to line.