SEEING THINGS THAT AREN'T THERE?

Imagine opening a bag of French fries and Santa Claus is looking at you. Or you turn a corner and see a smile as wide as a house.

People see faces in all sorts of everyday objects, but those faces aren’t real. They're illusions due to a phenomenon known as facial pareidolia.

Why exactly does this happen, and how far can this distortion of reality go?

Humans are social animals, and reading faces is an important part of our ability to understand each other. Even a quick glance at a person's face can help us determine if we've met them before, what mood they’re in, and if they’re paying attention to us. We even use facial features to make snap judgments about whether a person is trustworthy or aggressive. To pick up all this important information, humans have evolved to be very sensitive to face-like structures. Whenever we see something, our brain immediately starts identifying the new visual stimuli based on our expectations and prior knowledge. And because faces are so important, humans have evolved several brain regions that allow us to recognize them faster than other visual stimuli. While it takes our brains about a quarter of a second to recognize most objects, we can recognize a face in just a tenth of a second. So it makes sense that we prioritize faces over everything else.

However, imaging studies of the brain have shown that these regions may be too sensitive, causing them to recognize faces where there are none. In one study, participants reported seeing faces in more than 35% of the images presented to them with pure noise, even though nothing was visible. It may seem worrisome that our brains can get it wrong so often, but these fake faces may actually be a byproduct of something volutionarily beneficial. Since processing all the visual information we perceive quickly and correctly is a huge computational task for the brain, this kind of hypersensitivity could be a useful shortcut. After all, seeing fake faces is usually harmless, while overlooking a real face can lead to serious problems. But for hypersensitivity to be helpful rather than harmful, our brains must also be able to quickly tell when a face is real and when it's not.

So how quickly can our brains tell if they’ve been fooled?

To answer this question, researchers used a form of brain imaging called magnetoencephalography. By measuring the magnetic fields caused by electrical currents in the brain, this technique allows us to track changes in brain activity on a millisecond scale.

Using this tool, researchers have found that the brain generally recognizes a face as deceptive within a quarter of a second—

which is about the same time it takes us to recognize most visual stimuli without a face. However, even if our brain knows that the face isn't real, we can still see it in the object. By affecting these brain areas, we can further impair our ability to distinguish between reality and fiction.

In one study, researchers stimulated a participant’s fusiform face area while they looked at an object without a face. As a result, participants reported briefly seeing facial features even though the object remained unchanged. And while viewing a real face, stimulation of the same area resulted in perceived distortions of the eyes and nose. These studies suggest that certain features are critical for face recognition. As few as three dots can be enough to represent eyes and mouth. People even assign gender, age, and emotions to illusory faces. It's unclear whether a person’s culture or individual history affects these perceptions, but we do know that pareidolia isn't unique to humans. Rhesus monkeys show eye movements similar to ours when viewing pareidolic objects and real faces, suggesting that this phenomenon is deeply embedded in our primate social brains.

So the next time you see an unexpected face in a coffee, a car, or a closet, remember that your brain is working overtime to avoid missing the faces that really matter.