This optical illusion made with nothing but scraps of paper is going viral — here's how it works

• Akiyoshi Kitaoka is a psychology professor at Ritsumeikan University in Japan.
• His recent optical illusion demonstrating lightness perception went viral on Twitter.
• What looks like a color-changing square is a simultaneous contrast illusion. 

Psychology professor Akiyoshi Kitaoka studies optical illusions at Ritsumeikan University in Japan. 

He recently posted a demonstration of lightness perception that boggled the minds of Twitter users.

The optical illusion involves a piece of paper and a square moving across it. It appears that the square is changing colors as it goes from one side of the paper to the other.

Here's a video of what it looks like in action:

People couldn't figure out what was going on.

Kitaoka's color-changing square is what's known as a simultaneous contrast illusion. The explanation has little to do with the color of the square and more to do with the color of the background.

Our perception of color is influenced by what surrounds it. When the square is against a dark background, the brain registers it as a lighter color, and the square placed against a light background will look darker.

The square isn't changing colors, but its luminosity appears different against different backgrounds. 

This image presents another illustration of the illusion:

The horizontal bar is just one color, even though it appears to progress from light to dark grey when placed against a color gradient.

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