The best optical illusions are the ones you can try at home. Take the footstep trick below: All you need to recreate it is a white sheet of paper with black stripes and a transparent film sheet marked with yellow and blue blocks. It may look simple, but move the film across the page and the colored shapes will appear to shuffle forward like tiny footsteps.
The illusion, recently shared by The Kid Should See This, is the creation of Akiyoshi Kitaoka, a professor with the psychology department at Kyoto’s Ritsumeikan University. He explained the mechanism at work in a paper he published with psychology professor Stuart Anstis in 2015 [PDF].
According to the report, the colored blocks need to be two times the width of the black stripe and either light (like the yellow ones) or dark (the blue ones) for the trick to pay off. The illusion is all about contrast, so the colors are essential. The authors explain:
“When the dark blue squares lie on white stripes, they have high contrast (dark vs. white) and they appear to speed up momentarily. When they lie on black stripes, they have low contrast (dark vs. black) and they appear to slow down. The opposite is true for the light yellow squares.
Consequently, the squares appear to go faster and slower in alternation, like a pair of walking feet.”
The brain takes all sorts of shortcuts when it comes to perceiving color, and most of the time this goes unnoticed. But when an artist knows how to exploit this it can lead to some mend-bending tricks, like this image from Akiyoshi Kitaoka in which three colors appear to be four. Check out more of Kitaoka's psychedelic illusions on his webpage.
[h/t The Kid Should See This]