I’ve known about this for years but never shared it, as far as I can tell. It’s weird! — Dan

Pictured above is a photo of former U.S. President Barack Obama, and at first glance, there’s something unusual about it — it’s upside down. But other than that, it doesn’t look all that weird. It’s obvious who the picture is of, and there’s nothing about it that’s going to give you nightmares.

Until you look more closely. Or, more accurately, until you flip the photo right side up.

That version of the photo is below, but before you scroll a bit, let me warn you — it’s creepy.

Ready?

OK!

Yeah, that’s not what President Obama looks like. That’s his face, sure, but his eyes and mouth are flipped, making the whole experience unsettling. And yet, you probably didn’t notice that in the top photo, his eyes and mouth aren’t upside down, even though the rest of the image is.

What you’re experiencing is an optical illusion first discovered by Peter Thompson, a psychology professor at the University of York in 1980. Thompson, in a brief paper (here) demonstrated that if we take a person’s face and flip most, but not all of it, we can still figure out who the person is. Thompson used a composite photo of then UK Prime Minister Margaret Thatcher — you can see his images in the linked-to paper above — and dubbed the effect the “Thatcher illusion.” Today, it’s often called either that or the “Thatcher effect.”

The science community thinks this happens because when our brains process faces, we tend to do so holistically, not part by part. Instead of carefully checking on the eyes, mouth, and nose individually, our brains look at how they fit together as a whole. When a face is upside down, that whole-face processing doesn’t work as well, so strange details — like upside-down eyes or a flipped mouth — are harder to notice and may seem normal. But when the face is right-side up, our brains are much better at spotting anything that’s “off,” which is why the altered face suddenly looks so unsettling.

The practical impact of this is hard to say, but it serves as a reminder that our brains are very good at reading between the lines — or ignoring small mistakes — allowing us to see the full picture, even when it’s not really there.

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Today’s Bonus fact: The board game Go is played with two sets of stones, one black and one white. According to the Go Wikipedia entry (and I’ve tried to find a better source for this, but haven’t nailed one down, sorry!) the stones aren’t the same size: “Black stones are slightly larger in diameter to compensate for optical illusion of the white stones appearing larger when placed with black stones of the same diameter.”

From the Archives: Shadow Boxing: A and B are the same color. You’ll see (or will you….?)

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And thanks! — Dan