Thread by @AlexandraErin

So, here's a thing about accessibility and people without depth perception - when I was a kid, learning about binocular vision, the books said "You can see for yourself what it's like by closing one eye!"

Except, fun little wrinkle: this doesn't work so well.

This doesn't work so well because you don't see with your eyes, you see with your brain. So if you stand at the top of your stairs, trying to see if they're safe to someone without binocular vision, if you cover one eye... you won't see what they'd see, it's mostly unchanged.

Your brain does not require any additional information it does not have to keep rendering the three dimensional view of what it was just looking at in three dimensions. It's going to show you the stairs.

Now, if you try charging down them with one eye closed, you might be in for a bad time, because the view is rapidly changing and your brain's not getting new input.

Where your temporary lack of depth perception gives you a semi-accurate approximation of what it's like to have no depth perception is when you suddenly see something new popping up up close, or you're looking at an environment you've never seen before.

I used to be very confused about books telling me that if I just closed/covered one eye I would see everything without depth perception, and now I'm seeing discussions on Twitter about accessibility that mention depth perception and making space navigable/accessible without it.

So I just want to throw out there that if you're trying to make a space accessible from a point of view of depth perception, looking at it with one eye closed isn't going to tell you where the problems are.