Blindsight in Ordinary People
In the latest issue of PNAS, there's an article on blindsight in ordinary people: The researchers induced local and temporary blindness by magnetically de-activating certain parts of brain area V1. When forced to choose, the subjects then often guessed correctly the direction or colour of a patch which they didn't consciously see.
(As usual, "consciously" is here functionally defined: what the subjects were missing is not some kind of non-functional, phenomenal consciousness, but a state with a certain functional role, leading in particular to utterances like "I saw a yellow patch". A case of truly phenomenal blindsight would be somebody who behaves in every way as if she consciously sees the patches, but who nevertheless doesn't see them consciously.)
So there are neural pathways delivering quite specific visual information to cognitive states without passing through V1. If that's correct, then maybe we could also retrieve visual information from this source which gets lost by the neural processing in V1. To test this, I set up this little page, but at least for me, it doesn't give any interesting results.
The page shows a circle with four sections on a high contrast background. Three sections of the circle are somewhat transparent, one isn't. (Only works if your browser supports PNG alpha transparency, which just about every browser except Internet Explorer does.) But the high contrast background makes it look like all sections are equally transparent. Apparently, this is due to some processing in V1. So the information about which section is opaque might still be available through the other path. If so, we should guess correctly more often than not. But that doesn't work for me. Oh well.