Optical illusions are proof of how the brain works; here's why

A spinning grayscale ballerina, a person crammed neatly into a life-sized doll box, and a black-and-white prism that morphs depending on where you stand - those were the winners of the 2024 Best Illusion of the Year contest. According to NPR, the global competition attracts artists, magicians, vision scientists, and curious creators who spend months building tricks for the eye.

The event was co-founded two decades ago by neuroscientist and science writer Susana Martinez-Conde. She still cannot quite believe the stream of fresh entries every year. “Illusions are fundamental to the way that we perceive the world - the way that, frankly, we exist as human beings. Illusions are a feature and not a bug,” she told NPR’s Short Wave podcast.

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Optical Illusions in history

The fascination is not new. Aristotle described one of the earliest illusions more than 2,000 years ago. He called it the “waterfall illusion,” or motion aftereffect. Watch a river flow long enough, and suddenly the rocks nearby seem to drift too.

Over time, illusions like this became a scientific tool. Martinez-Conde has studied “Rotating Snakes,” a pattern that seems to move on its own. The effect, known as peripheral drift, exposes how the brain interprets motion even when nothing is shifting in reality.

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Why scientists care about optical illusions?

For researchers, illusions are more than party tricks. They are a way to look inside the machinery of perception. Martinez-Conde explains that when an illusion fools us, it shows how our neurons fire and how brain circuits work to build a version of reality. “We can analyze the neurons and the brain circuits that support neural activity that matches perception, and those could be part of the neural basis of consciousness,” she said.

That is the big draw for scientists. Every illusion is a crack in the system - and a chance to peek at how the mind shapes what we see.

What is next?

The contest is run by the nonprofit Neural Correlate Society. Voting for the 2025 edition will open next year, with entries expected from around the globe once again. If history is any guide, the submissions will prove that no matter how much we think we understand the brain, it always finds a way to surprise us.

FAQs

What is the Best Illusion of the Year contest?

It is an international competition showing creative visual illusions.

Who founded the contest?

It was co-created by neuroscientist Susana Martinez-Conde.

What were the 2024 winning illusions?

A spinning ballerina, a doll-box human, and a shifting black-and-white prism won the competition.

Why do scientists study illusions?

They reveal how the brain builds perceptions of the world.

When is the next contest?

Voting for the 2025 edition will take place next year.