Mind & Body

The Autokinetic Effect Is an Optical Illusion That Makes Stars Look Like UFOs

Here's an assignment: Stare at a bright, stationary point on a dark background. It could be a star in the night sky, a faraway streetlight, or a dot of white-out on black construction paper. Whatever it is, if you stare at it long enough, it will start to ... move.

Related Video: Check Out This Movement Illusion

Dancing Dots?

You're not losing your mind. In fact, you've been in good company throughout history. At the turn of the 19th century, long before your personal dot started to dance, German astronomer Alexander von Humboldt ran into this same phenomenon. Stargazing without his telescope, he perceived some stars in the sky to be moving. He decided this was an important discovery, and termed it "Sternschwanken," or "swinging stars."

It took decades for the scientific community to realize that von Humboldt hadn't unearthed secret star movements so much as the secret movements of his own eyes. See, the human eye moves a lot throughout the day, sometimes voluntarily and sometimes involuntarily. When you have a stable point of reference in your field of vision alongside the bright dot, your brain can edit out your eye movements, removing any blurring or twitchiness in what you see.

Get close to your screen and stare at this dot for 30 seconds. Can you see it move?

However, when your entire field of vision is filled with a white dot against a dark background — or in von Humboldt's case, multiple white dots — you lose the ability to distinguish between movements of your eye and movements of the dot. So when your eye muscles start to fatigue from staring and it causes slight eye movements, you mistakenly attribute the movement to whatever you're looking at.

This powerful optical illusion is called the autokinetic effect. "Auto" means self, and "kinetic" means motion — so it basically means self-created motion.

When You Can't Believe Your Eyes

This optical illusion is hard for human beings to cope with. We tend to trust our eyes over our other senses — you're more likely to hear an indignant "I saw it with my own eyes!" than "I smelled it with my own nose!" — so inexplicable motion causes a lot of confusion.

Von Humboldt only came up with the first of many ways of coping. His "swinging stars" theory has been debunked, but it's since been neatly replaced with the idea of UFOs. Many UFO sightings are, in fact, the autokinetic effect in action. The effect also explains why staring at the sky intensely, searching for UFOs around say, Area 51, helps you "find" them — the act of staring triggers the illusion of motion.

People also cope with visual confusion by conferring with other people who saw the confusing sight and reaching a consensus about it. For instance, in a 1935 study, Muzafer Sherif asked subjects to stare at a stationary spot of white light and then estimate how much it moved. Their estimates ranged from 20 to 80 centimeters — a wide range, given that the spot hadn't moved at all.

Later, Sherif put these subjects in groups of three, engineered so that each group had two people with similar estimates, and one person with an outlier estimate. The outlier always ended up agreeing with the other two after the group discussed. While this is widely thought to reveal a human instinct for conformity, it also shows that when we experience the autokinetic effect, we doubt our own eyes and seek an explanation (or even a description) of the event that's corroborated by other people.

In which case, here's another possible explanation for a UFO sighting, or a moving pinprick of light in the dark: You're seeing things. Not because you're crazy, but because you're a human with glitchy human eyes.

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For other ways your brain tricks you, check out "You Are Not So Smart: Why You Have Too Many Friends on Facebook, Why Your Memory Is Mostly Fiction, and 46 Other Ways You're Deluding Yourself" by David McRaney. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Mae Rice January 23, 2019

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