Puzzlement and confusion:
I close my eyes. I wave my hand in front of my face. It seems as though I can see the motion of my hand. Most people I've asked report the same.
It's possible that I do detect that motion. A certain amount of light penetrates the closed eyelids. I could be detecting differences in lighting as my hand passes before my eyes.
But on the other hand, most people, deep in a cave where there isn't a single photon to pierce the darkness, will report being able to see their hands moving in front of their faces. That this isn't a matter of picking up on visual stimulus is made clearer by our inability in such situations to detect another person's hand waved before our faces. It seems that our knowledge of the movement of our hand is somehow affecting our visual experience, or at least our judgments about our visual experience, without actually causing any visual input.
So: When my eyes are closed and I seem to detect my hand, am I actually visually detecting its motion? Or is what's going on more like what happens in a cave?
Let's do some science. Consciousness studies, in such matters, is pretty uncut. Maybe there's something out there on this, but I bet you'd have to dig pretty deep; and then you'd get a few weird articles from 1932 or something, or from a minor Japanese journal in 2001 -- articles that have never been cited, and that have strange, contradictory results. (I don't know this for sure, I'm just conjecturing based on past experience with similar questions.) If so, you can do novel experiments right there in your armchair.
Try facing different directions (toward a light source, away from a light source). Try closing your eyes more tightly, or occluding them with your other hand, or interposing an object between your eyes and your hand. That's what I did at least. I found myself sufficiently puzzled that I dashed downstairs and found a group of loitering undergraduates and had them all do it too! (This probably enhanced my reputation as a kooky professor.)
The results were complete uninterpretable chaos. For example, for myself: I seem to see it more strongly when I face a light source than when I face away. When I close my eyes tightly or put my other hand completely over them, I find myself uncertain about whether I have visual experience conditioned on the motion of my hand. If so, it is less. But when I put an occluding object between my eyes and my moving hand, say six inches in front of my face, I do think I still experience the motion of my hand, despite the fact that it can't be affecting me though that occluding object -- or at least that's how it seemed to me before I ran downstairs. I seem to be able to reproduce that effect only inconsistently. Others had different patterns of results.
If you're game to try, I'd be interested to hear your thoughts and experiences. Maybe I'll even work some of them into a presentation I'm hoping to give at the Association for the Scientific Study of Consciousness next month....
Friday, May 04, 2007
Puzzlement and confusion: