No, that doesn't seem to be it. Although an online test seems to suggest that I don't suffer from this, so that's nice to know.
What I'm thinking of has several apparently static figures on a screen, and as you look around the picture, things change when you're not looking at them (even though you think that you're looking at them, because the entire screen is in your field of vision the entire time). I think that mostly they change colour and stuff, but sometimes they disappear entirely. You can't just do this online, since there also has to be something to track your focus of attention, so I've only read about it.
Update: Discussion has moved on to a new thread.
The load more comments links are getting annoying (at least if you're not logged in), so it's time for a new Harry Potter and the Methods of Rationality discussion thread. We're also approaching the traditional 500-comment mark, but I think that hidden comments provide more appropriate joints to carve these threads at. So as of chapter 67, this is the place to share your thoughts about Eliezer Yudkowsky's Harry Potter fanfic.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six. The fanfiction.net author page is the central author-controlled HPMOR clearinghouse with links to the RSS feed, pdf version, TV Tropes pages, fan art, and more, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: