Yes, this seems reasonable, although I don't recognise the term.
ETA: Following Wikipedia's links, the stuff here from 8:30 to 10:00 seems most like what I'm thinking of, although still not quite as dramatic as what I remember.
By this point, it's possible that my memory is just faulty.
I think I saw a demo, or video a demo, about 15 years ago, of the ERICA gaze-tracking program at UVA where onlookers could see the screen change characters while the person whose gaze was being tracked couldn't see the changes. If I remember correctly, it was a screen of normal text in MS-Word or something that would mutate into gibberish where the user wasn't watching.
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: