I find myself doing that when very tired or under significant social stress, but you're right, the structure of the brain can't support that interpretation dire

I find myself doing that when very tired or under significant social stress, but you're right, the structure of the brain can't support that interpretation directly. I imagine that your brain could easily be experiencing it as a cue for self-trained rest states, so I don't want to misunderstand your experience as identical to my own, especially if you're doing it for 2-4 hours a stretch. My own interpretation of what is going on when I do it has been that it simply reduces (a) cognitive load (maybe) and (b) unnoticed eyestrain (more likely) by eliminating any attempt at depth perception.