In late December, the Neural Correlate Society announced the top designs in its annual Best Illusions contest.
The winning illusion is a 3-D interpretation of a classic optical illusion, the Shröder Staircase, Andrew Liszewski reports for Gizmodo. In the original, two-dimensional illusion, a series of zig-zagging parallelograms span a rectangle’s diagonal. Because the image lacks any indication of depth, your brain can interpret it in two ways: either a staircase going up from the ground, or a staircase coming down from the ceiling. In the 2020 winning illusion, a small cone placed at the apparent “top” of the staircase can reach the bottom without taking a single step. The staircase just has to be spun 180 degrees.
The first-place design was created by Meiji University mathematical engineer Kokichi Sugihara, a repeat winner of the contest. When Sugihara shows the illusion from new perspectives, he reveals that the “staircase” is actually a horizontal platform—its legs are the same height.
Sugihara created a printable version of the 3-D illusion that anyone can cut out and construct on their own in order to understand the design (or confuse their friends.)
Sugihara has designed several mind-bending illusions that won first place in 2010, 2013 and 2018, and earned him a place in the Top Ten every year in between. He specializes in ambiguous designs, like the 3-D Shröder staircase, which look like different shapes depending on the angle they’re viewed at, or the same shape at any angle.
"Historically, optical illusion has been a research topic in psychology. I introduced a mathematical approach to this topic, and thus can create new types of 3-D optical illusions," said Sugihara to CNN’s Jacopo Prisco by email in 2018.
Other mathematical illusions include a miniature garage roof that looks rounded on top from one angle, but simultaneously in a mirror, appears zig-zagged, and a set of columns that look square at one angle but circular in a mirror. Both designs won second place in the annual illusions contest during their respective years.
In 2020, second place went to Matt Pritchard for an illusion titled, “The Real Thing??”
Using simple materials like soda cans and cardboard, Pritchard set up scenes that resembled a can reflected in a mirror. The illusion is broken when someone picks up the soda can and throws it through the mirror—revealed to be an empty picture frame—where it knocks over the second can. The cleverly assembled scenes use colored backgrounds and quick movements to make it appear, at first glance, like the frame holds a mirror.
The effect is even trickier when a frame holds a mirror in one half, and is open on the other half, as in the last version of the illusion shown in the contest video.
“Careful examination will reveal discrepancies in the scene,” Pritchard writes in the illusion description. “But what causes the vision system to make the initial mirror assumption is not yet fully understood.”
Optical illusions are the result of the human brain’s tendency to take shortcuts when trying to understand what it’s looking at, says La Trobe University illusions expert and psychologist Philippe Chouinard to Catherine Offard at The Scientist magazine. Some illusions play with humans’ ability to interpret the size of an image depending on what else surrounds the image in question. Others, like Sugihara’s ambiguous objects, take advantage of forced perspective and a lack of depth perception to create seemingly impossible and contradictory pictures.
To explore all of the best optical illusions of 2020, visit the Illusion of the Year website.