This optical illusion will break your brain — but only for 15 milliseconds

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• This optical illusion, called the Pinna-Brelstaff illusion, exposes a lag in our brains.
• If you focus on the dot in the middle and move your head forward, the outer circle appears to rotate clockwise - move your head back and the motion changes.
• A study at the Chinese Academy of Sciences in Shanghai showed that monkey brains had a 15 millisecond delay when processing motion.

In a study conducted by scientists at the Chinese Academy of Sciences, these scientists proved that the brain experiences a delay when viewing some optical illusions, including the Pinna-Brelstaff illusion.

While it may just look like two circles surrounding a dot, look a bit closer. First, focus on the dot. Then start moving your head closer - the circles should appear to be rotating! Now, move your head back to normal, slowly. The circles just reverse direction and rotate the other way.

This illusion has been around for years, but it was never clear what caused it.

"It's kind of like if you're at a party where you're listening to a voice amongst lots of noise," Ian Max Andolina from the Chinese Academy of Sciences told New Scientist. "The physical motion is like background noise and the illusion is the voice in the noise you have to pick out. It takes a little longer to do that."

The study used macaques (a type of monkey they determined to perceive illusory motion similarly to humans) to show that there's a tiny - but significant - delay between the neurons in brains that perceive motion, aka the circles moving, and neurons that perceive local motion. The local motion neurons detect that nothing is actually moving, but it takes them a few beats to catch up with our eyes. 

What do you see?

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How long does it take your brain to figure it out?

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