Akiyoshi Kitaoka

Akiyoshi Kitaoka is a professor of psychology at Ritsumeikan University in Japan and the most prolific designer of still images that seem to move. Unlike most people on this site, whose best-known illusions were found decades or centuries ago, Kitaoka is a product of the internet age: his work has been published and shared online since the early 2000s, first among researchers and then everywhere.

Rotating Snakes

His best-known image, Rotating Snakes (2003), is a set of rings made of repeating segments in black, dark blue, white and yellow, always in the same order. Look at the centre and it's mostly still; let your eyes wander and the rings seem to turn steadily, although nothing on the page moves. People sharing it online often assume it's an animated image. The rotating snakes page has a version drawn by your browser, with switches that let you test which parts of the design matter.

It belongs to the family of peripheral drift illusions, still patterns that seem to move, most strongly out of the corner of the eye. With Hiroyuki Ashida, Kitaoka worked out which sequences of brightness produce the strongest drift and in which direction (Kitaoka & Ashida, 2003). The favoured explanation is that different brightness levels are processed at very slightly different speeds, so each eye movement or blink sends a staggered signal that motion detectors read as movement. Recordings from monkeys by Bevil Conway, working with Kitaoka and others, found direction-selective neurons responding to the snakes' brightness steps as if they were moving (Conway et al., 2005).

A huge catalogue

The snakes are only the most famous of a very large body of work. Kitaoka's website collects thousands of original illusions covering motion, brightness and colour, geometric distortion and more, and many of them have been used as stimuli in published research. He has also written about the history and mechanism of the drift effect, tracing it back to Fraser and Wilcox's 1979 discovery (Kitaoka, 2017).

Why his work matters

Kitaoka's work matters in two ways. Scientifically, his designs are strong, reliable and easy to vary, which makes them useful for studying how timing differences in early vision are misread as motion: change the order of the tones and the direction reverses; lower the contrast and the effect fades. Culturally, he showed that illusions could be native to the social web, instantly shareable and needing no explanation. That combination, rigorous enough for journals and accessible enough to go viral, is why the rotating snakes are among the best-known illusions of the century.