It’s kind of humbling when you think about it—our brains are powerful, yet it doesn’t take much to trick them. A simple optical illusion is enough to throw them off. But how exactly do these illusions work? To find out, Bored Panda reached out to Mark Changizi, a cognitive scientist and author of The Vision Revolution and Motorcycle Mind.
“Optical illusions occur because your brain is slow,” Changizi explains. “It takes about a tenth of a second to generate a perception, meaning that if your brain simply registered the world as it was when light hit your retina, your perception would already be outdated. In that fraction of a second, even at a slow walking speed of 1 m/s, you would have moved 10 cm. Now imagine running or catching a ball—reacting to the past wouldn’t cut it.”
“To compensate, your brain has evolved to anticipate the immediate future,” Changizi continues. “Instead of rendering a perception of the past, it predicts what will happen next and generates a perception of that future moment. By the time the perception is formed, reality has caught up, allowing you to experience the world in real-time.”
According to Changizi, many optical illusions take advantage of this predictive system.
“A common example is illusions featuring radiating lines, which your brain interprets as blur streaks—like those you experience when moving forward, where the visual field expands outward, similar to the Starship Enterprise jumping to warp speed,” he says.
The Hering Illusion, discovered in 1861 by German physiologist Ewald Hering, is a perfect showcase of this effect. Two straight vertical lines sit over a background of radiating lines, similar to bicycle spokes, yet somehow, your brain insists they’re curving. Look closer, and you’ll see they never moved at all.
“If you were actually passing through a tall cathedral door, for instance, its sides would appear to warp in your visual field in exactly this way—far apart at eye level but converging higher up,” says Changizi. “Your brain applies that same warping perception here, even though you’re standing still, creating the illusion.”
You might think that falling for illusions means your brain is making a mistake, but that’s not the case. In fact, these illusions prove just how advanced our brains are.
“These illusions reveal how your brain processes the world in real-time,” Changizi says. “While illusions may trick you in controlled settings, in everyday life your brain is constantly receiving optic flow and other cues about how the world will change in the next moment. By using those cues to generate a perception of the immediate future, it allows you to experience the present instead of lagging behind.”
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“This predictive mechanism is essential for navigation, coordination, and reacting quickly to your environment,” he adds. “In short, the same system that makes illusions possible is what allows you to function seamlessly in the real world.”
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