As long as you can fit your perceptions into a coherent whole, Bel, I don't see the epistemological problem. If you think you see something out of the corner of your eye, then look at it and discover it isn't there, IMO it's probably not. You're not crazy yet.
Anyways from I recall of the way vision works, we actually "see" far less than we think we do, in terms of directly perceiving the visual characteristics of an image. Especially when we're not looking directly at it. Rather, the brain has a bunch of "filters" for recognition and so forth, which it applies to images. Once it decides that an object is a cat, or a tree, or your girlfriend, it "fills in" your mental perception based on what that looks like.
The blind spot is a similar type of thing. We don't perceive there being a "blank" point there -- it seems we see our whole field of vision but really we don't.
So all you need to see something that isn't there is to have some recognition circuit-thingy triggered incorrectly, maybe by the chance characteristics of an image matching the pattern too well, maybe just randomly. Seems reasonable that this kind of thing would happen more often when you're stressed, tired, etc.
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There was a good article about this in the Telegraph recently:
http://www.telegraph.co.uk/connecte...illa05.xml&pos=portal_puff1&_requestid=347199
Look around, and you could be forgiven for believing that you can see a vivid and detailed picture of your surroundings. Indeed, you may even think that your eyes never deceive you. Unfortunately, the same cannot be said for your brain.
Scientists have gathered some remarkable evidence which shows that it is possible to see something without observing it, in research that sheds new light on traffic accidents that occur when a driver "looked but failed to see", and other examples of mayhem and mishap in everyday life.
... In one experiment, people who were walking across a college campus were asked by a stranger for directions. During the resulting chat, two men carrying a wooden door passed between the stranger and the subjects. After the door went by, the subjects were asked if they had noticed anything change.
Half of those tested failed to notice that, as the door passed by, the stranger had been substituted with a man who was of different height, of different build and who sounded different. He was also wearing different clothes.
Despite the fact that the subjects had talked to the stranger for 10-15 seconds before the swap, half of them did not detect that, after the passing of the door, they had ended up speaking to a different person. This phenomenon, called change blindness, highlights how we see much less than we think we do.
Working with Christopher Chabris at Harvard University, Simons came up with another demonstration that has now become a classic, based on a videotape of a handful of people playing basketball. They played the tape to subjects and asked them to count the passes made by one of the teams.
Around half failed to spot a woman dressed in a gorilla suit who walked slowly across the scene for nine seconds, even though this hairy interloper had passed between the players and stopped to face the camera and thump her chest.
However, if people were simply asked to view the tape, they noticed the gorilla easily. The effect is so striking that some of them refused to accept they were looking at the same tape and thought that it was a different version of the video, one edited to include the ape.
They link to the ape video -- it's really freaking amazing.
it went away.
