Ten years ago, when I visited the Luray Caverns in Virginia, the tour guide took us down to the deepest cave and turned off the lights. He told us to wave our hands in front of our faces and asked if we could see our hands waving. We could, faintly -- or so we thought. He then asked us to wave our hands in front of our friends' faces. Our friends' hands we couldn't see at all. When we thought we could see our own hands we were fooling ourselves, he said. Not a single photon penetrated that darkness; no light actually came from our hands into our eyes.
Call this the spelunker illusion. The existence of this illusion appears to be common lore among avid cave explorers. I have also confirmed it in more pedestrian lightless environments. Yet no psychologist discusses it in any of literature I've reviewed in writing my forthcoming chapter on visual experience in darkness. But surely someone must have written a treatment? If you know of any discussions, I'd appreciate the reference!
I see three possible explanations of the spelunker illusion:
(1.) The brain's motor output creates hints of visual experience in accord with that output.
(2.) Since you know you are moving your hand, your visual system interprets low-level sensory noise in conformity with your knowledge (much as you might see a meaningful shape in a random splash of line segments).
(3.) There is no visual experience of motion, but the spelunker mistakenly thinks there is such experience because she expects there to be.
There might be other explanations too. I can see how we might start to empirically tease apart the three explanations above. For example, (1) and (2) seem to come apart if you have your friend move your passive hand rather than actively moving your hand yourself. And (3) can come apart from (1) and (2) if we can quash the expectation of experience.
Is this a mere curious triviality? Maybe. But the three explanations above do bear somewhat differently on different theories of sensory experience and our knowledge of it. Like other illusions, this illusion promises to reveal something about the hidden operation of the visual system, if it can be properly understood.
Update, April 28, 2014:
Leonard Rosgole and Miguel Roig point out to me that these phenomena were reported in the psychological literature in Hofstetter 1970, Brosgole and Neylon 1973, Brosgole and Roig 1983. They have since been confirmed by Dieter et al. 2013. If you're aware of earlier sources, I'd be curious to know.