Why Do We See the Man in the Moon?

Take a look at the slideshow above. The photos depict, in order: tower binoculars, a tank tread, tree bark, headphones, a tray table, a toilet, eggs, and more tree bark. Yet I perceived every one of them as a face, and I bet you did, too.

That’s because, as I wrote about a few weeks back, most people are obsessed with faces. We see faces everywhere, even in things that are most definitely not faces. The most famous example is probably the man in the moon. The weirdest has got to be the person who reportedly paid $28,000 for an old grilled cheese sandwich whose burn marks outline the face of the Virgin Mary.

This phenomenon, called face pareidolia, isn’t new (Leonardo da Vinci even wrote about it as an artistic tool). But nobody knows much about how or why our brains create this illusion. This week I came across a fascinating brain-imaging study that begins to investigate these questions. The paper, published in the journal Cortex, is titled “Seeing Jesus in Toast,” and this fall it won an Ig Nobel Prize, awarded “for achievements that first make people laugh then make them think.”

The study hinges on a clever method for inducing pareidolia inside of a brain scanner. The researchers showed 20 volunteers hundreds of “noise images” — squares comprised of black, white, and gray blobs — and told them that half of the images contained hard-to-detect faces. (The participants had been through a training period in which they saw clearly defined faces in such images, so they were used to the act of searching for a face within the noise.) After seeing a noise image, the volunteer would press a button indicating whether she saw a face in it or not. Unbeknownst to the participants, none of the noise images contained any overt faces.

The scientists reasoned that trials in which participants reported seeing a face were examples of pareidolia. To confirm this, the researchers took all of the images in which a participant saw a face and combined them into an average image. They then subtracted from that the average of all of the images in which the same participant did not see a face. The result of that subtraction, somewhat amazingly, was a crude face shape, suggesting that participants really were experiencing face pareidolia.

A week later, the same participants came back in the lab and went through a similar procedure. This time, though, they were told that half of the noise images they saw contained a hard-to-detect letter. In reality, none of them did — in fact, the images were exactly the same as those they saw the previous week.

All of these experiments happened inside of a brain scanner, allowing the scientists to compare which parts of the brain are activated during face pareidolia, letter pareidolia, and no pareidolia.

It turns out that a particular brain area — the right fusiform face area (FFA) — showed enhanced activation during face pareidolia but not letter pareidolia or no pareidolia. What’s more, the higher a volunteer’s activation in the right FFA, the more her subtracted composite image looked like a face, the study found.

This is an intriguing finding, the researchers say, because of what’s already known about the FFA. Previous studies had found that this area is specialized for processing true faces (hence the name). The fact that it’s also active for these imagined faces suggests that it’s involved in our more abstract conceptions of faces, as opposed to simply responding to the basic visual pattern of two eyes on top of a nose.

And why do our brains so easily create faces? There’s a compelling evolutionary explanation, the researchers write. “This tendency to detect faces in ambiguous visual information is perhaps highly adaptive given the supreme importance of faces in our social life.”

Regardless of what’s going on in my brain, there’s something delicious about looking at photos of face pareidolia, don’t you think? If you have your own examples, please share — the weirder the better!

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