How Do Optical Illusions Work?

We rely on our eyes to inform us of what’s going on in the world. Where am I going? Who am I talking to? It’s an essential part of life and that’s why optical illusions can be such a spooky thing! Is seeing really believing?

The History of Optical Illusions

Optical illusions date all the way back to ancient Greece. Not surprisingly, the first mentions of optical illusions were brought forth by one of the greatest minds ever recorded, Aristotle. Aristotle discovered the ‘motion aftereffect’, otherwise known as the waterfall illusion. When you look at a waterfall and shift your eyes to look at static rocks, the rocks will appear to be moving in the opposite direction the water is flowing. Wondering what the science is behind this phenomenon? While your eyes track and adapt to the motion of the water flow, they are actually wearing out certain brain neurons. Therefore, when you shift your eyes over to the rocks, the other competing neurons over-compensate, resulting in the illusion that the rocks are moving in the other direction.

Aristotle’s discovery of the waterfall illusion represented the first notion that seeing may not actually be believing. Our senses can indeed betray us and create illusions! Here are some other popular optical illusions:

Ebbinghaus Illusion

One great pioneer of the study of optical illusions was Hermann Ebbinghaus. He was such a prominent scholar in the field that he actually has an illusion named after him! His illusion is a play on size perception (as pictured below) and is still used extensively today in the study of cognitive psychology.

Ponzo Illusion

Another popular illusion that plays with the eye’s perception of depth is known as the Ponzo Illusion (pictured below). It plays on our brain’s perception of linear perspectives, with two lines appearing to be different lengths when placed between converging parallel lines.

Penrose Triangle

The Penrose triangle appears to form a standard triangle except for the one intersection angle that suddenly changes perspective! The side disappears to become a different side of the triangle, resulting in the illusion that the triangle is folding in on itself.

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