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This photo of someone's shiny legs is an illusion

I’m really worried about my editor, Erin.

She’s blown up an image on her screen, is squinting at it, and keeps wandering back and forth to see it from different angles.

But whatever she’s trying to do, it isn’t working:

Erin in slackSlack

Here’s the photo that’s causing this kerfuffle:

As my colleague Jacob Shamsian explains, the weirdly glossy look of the legs is actually an illusion. Instagram user Hunter Culverhouse created it by accident.

“[I] had some white paint left on my brush and put random lines on my legs, turned out to be a completely confusing picture for everyone on the internet,” Culverhouse told Shamsian in an email.

All I can see is bizarrely glossy legs. But some people don’t see the shine at all, just some boring old white paint.

The illusion is freaking people out all over the internet.

Why do some people see the shine? Why do others see the white paint? My theory: The smaller it shows up on your screen, the more it looks like shine.

My own ideas aside, there’s a deeper level to what’s going on here. The photo is revealing that our eyes aren’t actually windows onto the real world. Instead, they gather lots of bits of information, which your brain assembles into a coherent stream of images based on what it knows about the real world.

Illusions are flaws in that system, which shine a light on how amazing it is in the first place.

The psychologist Claus-Christian Carbon explains in his paper “Understanding human perception by human-made illusions” why optical illusions like these legs or The Dress are so exciting:

We can … interpret illusory perceptions as a sign of our incredible, highly complex and efficient capabilities of transforming sensory inputs into understanding and interpreting the current situation in a very fast way in order to generate adequate and goal-leading actions in good time … By taking into account how perfectly we act in most everyday situations, we can experience the high “intelligence” of the perceptual system quite easily and intuitively.

In other words, when your brain misinterprets a visual clue — like the lines on Culverhouse’s legs — it lets us know a bit more about how it builds images of the world the rest of the time, when it works properly.

And for some people, like Erin, the visual system works too well to trick, even with an illusion this effective.

What do you see?

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