I don’t know if this is deep enough for GQ, and maybe there’s a perfectly simple answer, but…
You’ve all heard the phrase “Their eyes met across a crowded room”. I’m talking about the phenomena where you’re looking in the direction of a person, and suddenly your eyes meet and both of you knows it.
How do we know? Is it some sort of intelligence recognition? Is it ESP? (no, I don’t really believe in ESP).
I know there’s limitations because if I’m not wearing my contacts I can’t see very well across my desk, let alone across the room, so I’d have no idea if you’re meeting my eyes or not.
I don’t think people do know for sure. There have been instances where I thought someone was looking and talking to me, but it was someone behind me. I believe we just see that the person is looking at our direction, and in most circumstances, assume they notice us looking at them and are looking back.
Well, the geometry of binocular vision means that you can look at someone’s eyes (provided they don’t have a lazy eye or corrective lenses that distort the appearance of their eyes) and tell what direction each of their eyes is pointed. By observing the azimuths (angular direction) of each eye you can mentally calculate where the angles intersect – that’s the focus. This leads to the expression “thousand-yard stare” among others, describing eyes that don’t appear to focus on a nearby point at all.
From across a room, you could conceivably see enough of the whites of someone’s eyes to determine that their eyes were focused on your immediate vicinity. And of course, you have to look at their eyes to figure that out – so if they are looking at your eyes, they can also immediately deduce that you are looking at theirs.
As snailboy pointed out (and as you’d know if you’ve ever watched a bittersweet romantic comedy) it’s possible to make mistakes, and assume someone is looking in your eyes when they’re actually looking behind you or slightly to one side of you.
