I saw Simon Singh, author of 'Big Bang', use your Stairway to Heaven backwards lyrics in a lecture to make a point about how the brain imposes order on gibberish when it expects to find order, like words, where there is none. I am an ophthalmologist, and specialize in glaucoma. This is exactly the same thing the brain does when a glaucoma patient begins to lose peripheral vision. They are not aware that they have blind spots in the periphery of their visual field because the brain fills in the blank spots by continuing the pattern in the area surrounding the blind areas. This pattern completion is a lot like what goes on in interpreting the backwards Led Zeppelin lyrics.