Humans Fall for Optical Illusions, But Do Cats?

Peripheral Drift Illusion

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

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Comments (12)
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  • Ronny says:

    Well I don’t know about cats, but I can’t see any rotating snakes in that pattern. (?)

  • Donald Zepp says:

    I couldn’t initially see movement, but as I stopped worrying about it, it became apparent. For me, it’s a subtle rotation–If a cat sees it the way I do, I can see why it would be of interest to it, as it’s that tiny little motion that seems to get their interest.

  • david attic says:

    the effect of some of these illusions are more pronounced the bigger the image is, if you’re not seeing the effect here, perhaps try enlarging the image.

  • Mike Springer says:

    Yes, David. I think you’re right. I’m now having the same problem Ronny is describing, and I think it’s due to the size of the image. Like Donald, I see it here as a very subtle effect. Perhaps we can change to a different image later, but in the meantime you can click here to see a larger image in a new window.

  • John Conolley says:

    The cat might see something drift, but by God, I don’t. I blew it up to full screen size, and even bigger than full screen size, but I never saw anything drift.

  • Mike Springer says:

    We’ve changed the image to a detail view with larger circles, and the effect is much more clear now. So I hope that helps. If you’re interested I would still recommend you follow the link in my previous comment to a larger image. The effect is extremely pronounced in that one.

  • gennepher says:

    I can see this best on the 4 big circles pic at the top of this page (the larger pic format barely works for me). I am looking at this on an iPad screen

    The two circles on the left rotate left for me, and the two circles on the right rotate right for me…it ‘feels’ like maybe 2 or 3 revolutions a minute. It seems quite lively to me.

  • david attic says:

    it could just be this particular image too, i have friends who also don’t really get the effect, but if i show them something like this: or something else, they do.

  • Adam says:

    Folks I honestly don’t know what are you talking about! How come you can’t see any motion (illusionary motion) on the picture? I can see some even in the miniature… Please stop making fun of the admin ;)

  • david attic says:

    not i, i’m a huge fan of this stuff, i try to hunt down new stuff on a regular basis.

  • Patrycja says:

    Anyone who owns a cat knows that video proves nothing. It’s normal play behavior with a piece of paper. That’s right, cars don’t need toys; just string, a rubber band, and/or a piece of paper.

  • Priscilla Winslow says:

    That cat doesn’t seem to be stymied at all. He’s figured out that it’s an illusion and he’s stopped playing with it.

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