Consuming volumes of horror movies and candy corn may cause the mind to go wild, but stop yourself from spiraling when you see — oh, I don’t know — Albert Einstein’s face in your office’s ceiling tile. It’s not the theoretical physicist attempting to make contact from the beyond; it’s a scientific phenomenon called pareidolia.

Humans see faces in clouds or toast or on the surface of Mars thanks to our evolved perceptual systems. Processing patterns, like registering if that thing in the distance is a human, is biological.

This Halloween, combat mystical trickery with science with this excerpt from The Skeptics’ Guide to the Universe: How to Know What’s Really Real in a World Increasingly Full of Fake (out October 2) by Dr. Steven Novella with Bob Novella, Cara Santa Maria, Jay Novella, and Evan Bernstein.

Pareidolia refers to the process of perceiving an image in random noise, such as seeing a face in the craters and maria of the moon.

If you look at any walls spotted with various stains or with a mixture of different kinds of stones, if you are about to invent some scene you will be able to see in it a resemblance to various different landscapes adorned with mountains, rivers, rocks, trees, plains, wide valleys, and various groups of hills. You will also be able to see diverse combats and figures in quick movement, and strange expressions of faces, and outlandish costumes, and an infinite number of things which you can then reduce into separate and well-conceived forms. —Leonardo da Vinci

At some point in your life, probably when you were young and carefree and had more time than you knew what to do with, you lay on the ground and looked up at the clouds. Clouds are beautiful, their structures are fascinating, and they can give you a little perspective on how massive the world really is. But it’s also fun to try to find images lurking in the white vaporous billows.

While animals and faces are common patterns to see floating overhead, no one actually thinks (or should think) the detailed shapes of clouds are anything but random. We intuitively understand that when we “see” a bunny rabbit in a cloud, we are just imposing that pattern onto the randomness. But this phenomenon goes much deeper than just children imagining a sky menagerie, and it reflects how our brains process and interpret information.

The term for this phenomenon is pareidolia, which refers to the perception of familiar yet meaningless patterns in random stimuli or noise. It usually applies to seeing visual patterns, but sometimes the term is used to refer to other sensations, such as sound (in which case it might be called, fittingly, audio pareidolia).

Where's the face?

The technical term for the more general phenomenon of seeing patterns where they do not exist is apophenia, the tendency to see illusory patterns in noisy data. The information doesn’t even have to be sensory; the pattern can be in numbers or in events. (In this way conspiracy theories can result from apophenia — seeing a nefarious pattern in random or disconnected incidents.)

There’s nothing inherently wrong with seeing a face in a taco shell; it’s just a by-product of our evolved perceptual systems, like many of the other illusions to which humans fall prey. Our skills in this regard are so nuanced and powerful that even multimillion-dollar petaflop supercomputers still struggle to match us.

Neurologically there are two important reasons for the human tendency to see patterns in noise. The first is that our brains (unlike computers) are organized for massive parallel processing. This is an ideal arrangement for finding patterns, making associations, and sifting through large amounts of data.

Second, our perception is an active constructive process. Part of this process is taking an image and then quickly sifting through our catalogue of all possible matches, finding the best match, and then assigning it to the image. That blob looks like a horse, so your brain matches it to a horse and then backfills the details to make it look even more like a horse.

This works for speech as well. You hear sounds that your brain interprets as phonemes (parts of speech). It then searches through its database of phonemes and words until it finds the best match, and then that is what you hear.

Expectation plays a huge role in this process. That’s why, once your friend says, “Hey, don’t you see the dragon in that cloud? There’s its head,” the image pops into existence. Your brain found the pattern, and its construction of that image snaps into place. Or, if someone tells you that if you play “Stairway to Heaven” backward you can hear Robert Plant say, “Here’s to my sweet Satan,” then you’ll hear the supposed devil worship.

Pareidolia, seeing faces in random shapes, is a type of apophenia, which is a more generalized term for seeing patterns in randomness.

Though pareidolia can manifest itself in many ways, involving any of our senses, it’s the simple human face that is the poster child for this phenomenon. I remember watching a horror anthology series once in which a woman kept seeing ominous faces in the patterns on her ceiling. She asked if anyone had ever wondered why we tend to see faces more than anything else in these patterns. The answer, on that particular show, was that the faces were demons from another dimension. The real answer is far more interesting, if less spooky. Our pattern recognition skills in general are quite robust, but we have an especially sensitive knack for seeing faces.

There is a known neurological reason for this affinity for human faces: A dedicated part of the visual association cortex, the fusiform face area (FFA), specializes in recognizing and remembering them. Damage to the right FFA — from a stroke, for example — may cause a condition known as prosopagnosia, which is an inability to recognize faces. People with severe prosopagnosia cannot even identify their spouse or family members by sight alone. There is also developmental prosopagnosia, which is a relative deficit and can be mild.

It’s no wonder that a facial pattern is preferred by the human brain. We can see this even in young babies. They will spend more time looking at a human face than another image of similar complexity.

It’s easy to imagine why evolutionary selective pressures would favor this hyperability to see faces, given that we are such a social species. Our ancestors who were better able to quickly distinguish friend from foe, or determine the emotional states behind faces, probably had a survival advantage. Face and face-like recognition actually occurs subcortically (in the deep parts of the brain). This subconscious analysis appears to happen even before the image is passed along to other parts of the brain for more intricate processing. It’s clear why this would be an advantage — quickly recognizing that someone is quite pissed at you and about to bash in your brains can do wonders for your survivability.

The most famous face seen as a result of pareidolia has got to be the Face on Mars. In 1976, NASA’s Viking spacecraft was imaging Mars when it produced a picture of a mesa or butte in the Cydonia region that looked like a face. The scientists knew the face was pareidolia even if they didn’t know that specific word. They were used to what the tricks of light and shadow could produce on the varied terrain of Mars. But popular culture enthusiastically absorbed the Face on Mars and gave it a life of its own. Books such as The Mars Mystery and The Monuments of Mars have been written about it, and countless “documentaries” have discussed the significance of that face and what it means for the history of Mars and life on that planet. (Um . . . nothing?)

 pareidolia in a pickle
Here are some pickle faces.

The “face” is little more than a half-darkened visage with only one eye, a mouth, and a dot for a nose visible. The nose was actually a data dropout in the transmission that happened to be placed where the nostril would be. When NASA took a higher resolution image in

1998, it became obvious that the face was just an eroded pile of rocky detritus, no more an intentional face than the bumps on your ceiling.

Other worlds in our solar system and their surface features are also a great source of raw material for pareidolia. NASA has imaged Kermit the Frog, Bigfoot, and a giant smiley face on Mars. There is a nice picture of Homer Simpson on Mercury, and countless “alien artifacts” on the moon and elsewhere. UFO conspiracy theorist Richard Hoagland (you have to say “Hoaaaglaaand” as if you are Colonel Klink from Hogan’s Heroes) has practically based his entire career on pareidolia of NASA images.

Even on Earth there are impressive examples of pareidolia, of which the app Google Earth has made an easy pastime. My favorite is Medicine Hat, Canada, which shows a profile of a woman apparently wearing earbuds (the wire of the earbuds is an access road).

Perry and I once investigated the face of the Virgin Mary on a tree in Hartford near where we live. It was just the usual swirly patterns in tree bark, but a little bit of pareidolia turned that into a face, and cultural belief did the rest. Thousands of faithful camped out around this tree, convinced they were witnessing a miracle. To Perry and me it was simply tree bark — and a rather bland example of a quirk of brain processing.

When looking at these popular examples of pareidolia, it seems they cannot just be random. But that’s all part of the trick of how your brain constructs these patterns. Details that don’t fit the pattern are deemphasized. Those that are important to the pattern are made more prominent. Missing details are filled in. Your brain connects the dots. It’s amazing how few details are needed to suggest a face, and even an emotional expression, to our pattern-seeking brains. Even as little as a couple dots for eyes and some kind of line for a mouth is enough for our brains to see Elvis or the Pope.

Pareidolia can be fun, but if you aren’t aware of our penchant for and love of patterns, an interesting and diverting illusion can feed into a delusion. As we will see, some illusory patterns are more nefarious than just seeing a bunny rabbit in a cloud.

Excerpted from THE SKEPTICS’ GUIDE TO THE UNIVERSE: How to Know What’s Really Real in a World Increasingly Full of Fake by Dr. Steven Novella with Bob Novella, Cara Santa Maria, Jay Novella, and Evan Bernstein. Copyright © 2018 by SGU Productions, LLC. Used by arrangement with Grand Central Publishing. All rights reserved.