Human vision is both amazingly good, and surprisingly weird.

Good, because try taking a photo of the Moon and comparing it with what you can see with your eyes.

Weird, because of all the different ways to fool it. The faces you see in clouds. The black-and-blue/gold-and-white dress (I see gold and white, which means I’m wrong). The way your eyes keep darting all over the place without you even noticing.

What happens if you force your eyes to stay put?

I have limited ability to pause my eyes’ saccade; I have no idea how it compares to other people, so I assume anyone can do what I have tried.

On a recent sunny day, in some nearby woodland, I focused on the smallest thing I could see, a small dot in the grass near where I sat. I shut one eye, then tried to keep my open eye as still as possible.

It was difficult, and I had to make several attempts, but soon all the things which were moving stood out against all the things which were stationary. That much, I expected. What I did not expect was for my perception of what was near the point I was focused on to change.

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I didn’t take photos at the time, but this mock-up shows a similar environment, and an approximation of the effect. One small region near the point I was looking at tiled itself around much of my central vision. I don’t think it was any particular shape: what I have in this mock-up is a square, what I saw was {shape of nearby thing} tiled, even though that doesn’t really work in euclidian space. If I let my vision focus on a different point infinitesimally near the first, my central vision became tiled with a different thing with its own shape. The transition from normal vision to weird tiling felt like it took about a second.

How much of this is consistent with other people’s eyes (and minds), I don’t know. It might be that all human vision (and brains) do this, or it might be that the way I learned to see is different to the way you learned to see. Or perhaps we learned the same way, and me thinking about computer vision has literally changed the way I see.

Vision is strange. And I’m not at all sure where the boundary is between seeing and thinking; the whole concept is far less clear than it seemed when I was a kid.