Most “optical illusions” are not really optical. They have less to do with the way the eyes work than with the way the brain processes the information sent to it from the eyes. For this reason, many scientists prefer to call them visual illusions. So if visual illusions are a trick of the brain, and human brains differ from the brains of other animals, does that mean our visual illusions are uniquely human?
The answer would appear to be no, judging from the cute video below from YouTube. The kitten is falling for the “rotating snakes illusion” developed in 2003 by Japanese psychologist Akiyoshi Kitaoka. The rotating snakes (click here to view in a larger format) are an example of the “peripheral drift illusion,” a phenomenon first described in 1999 by Jocelyn Faubert and Andrew Herbert of the University of Montreal. Cats are very adept at perceiving motion in their peripheral vision. It helps them elude predators and home in on their own prey. But this kitty is thrown for a loop by the illusory motion of the rotating snakes.
The peripheral drift illusion occurs when circularly repeating figures with regular sawtooth patterns of light and dark are viewed in the periphery. You’ll find that if you move your eyes around the various circles, for example going from center point to center point, the circles in your peripheral vision will appear to be moving but the one you are focused on will not. If you stop moving your eyes, a moment later the circles will all appear to stop moving. In the abstract of their 1998 paper (open PDF), Faubert and Herbert write:
Illusory motion is perceived in a dark-to-light direction, but only when one’s gaze is directed to different locations around the stimulus, a point outside the display is fixated and the observer blinks, or when the stimulus is sequentially displayed at different locations whilst the observer fixates one point. We propose that the illusion is produced by the interaction of three factors: (i) introducing transients as a result of eye movements or blinks; (ii) differing latencies in the processing of luminance; and (iii) spatiotemporal integration of the differing luminance signals in the periphery.
via Stephen Law