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 (11)
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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.

  • 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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