I could have put this in the biology forum, but decided it has too strong a philosophical slant (as my questions always seem to). I recently read that the experiment where people who wore vision-inverting glasses having there vision eventually flip is a myth. This reminded me of a question I always had on the issue. What does it even mean for your vision to flip, and what does it mean when people say your brain inverts your vision from your eye? Inverts it relative to what? It seems to me that it is a meaningless question since there is no reference for up and down other than your experience of it. On the other hand, wearing inverting glasses causes the experience of having your vision flipped, but is this just relative to our auditory and proprioceptive cues?