The Dynamic Ebbinghaus Illusion

We’ve all seen amazing examples of illusions, but did you know that there is a fertile community of researchers creating new ones? The Best Illusion of the Year contest and website provide a showcase for celebrating illusions.

This year’s winner for best illusion was created by Christopher D. Blair, Gideon P. Caplovitz, and Ryan E.B. Mruczek from the University of Nevada, Reno. It’s called the Dynamic Ebbinghaus Illusion. When I viewed the illusion on YouTube, I was very impressed. And since the illusion featured circles that moved and changed size, it seemed very likely that I could replicate it using Sketchpad.

Of course, there was really no need to build the illusion from scratch, but once you’re hooked on mathematical constructions, it’s hard to resist a new challenge.

Below, you can see what I made. Press Animate to set the circles in motion. As the circles move, the six outer circles grow and shrink. But what about the central circle? It appears to grow and shrink as well, but amazingly, that is an illusion—the central circle does not change size at all! To check, although I’m sure you still won’t be convinced, press Hide Outer Circles while the circles are in motion.



3 thoughts on “The Dynamic Ebbinghaus Illusion”

  1. This is cool! Tawnia and I held a piece of paper over the central circle to prove to ourselves that it stayed the same size 😉

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