Cover Image: April 2009 Scientific American Magazine See Inside

Illusions in Motion: The Power of Symmetry

Our brain's preference for symmetry influences how we perceive motion














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The coupling of motion and direction is based partially on the objects’ synchronicity in time (and speed). Physiologists have proposed that such perceptual groupings may arise when there is synchronization of nerve impulses that are evoked in multiple brain regions by the individual quartets or ballerinas. If so, what happens if ballerinas in different parts of the visual field spin at speeds slightly different from one another? Would they still get synchronized? What if ballerinas were of nonuniform sizes? Could you uncouple large and small ones then? Have fun!

Note: This article was originally printed with the title, "The Power of Symmertry".


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ABOUT THE AUTHOR(S)

VILAYANUR S. RAMACHANDRAN and DIANE ROGERS-RAMACHANDRAN collaborate on studies of visual perception at the Center for Brain and Cognition at the University of California, San Diego. They serve as mem­bers of the board of advisers for Scientific American Mind.


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  1. 1. Ellipsoid 11:30 AM 5/1/09

    I find that I can easily flip the direction of the dancer by looking at her shadow. Is this because my brain applies the "clockwiseness" of the clockwise dancer to the counterclockwise shadow, thus flipping the spin of the whole shebang?

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  2. 2. Cristi Stoica 06:38 AM 5/3/09

    In
    http://www.unitaryflow.com/2008/10/spinning-dancers-mistery.html
    it is explained with animated images why the "spinning dancer" is perceived by most of us as spinning clockwise.

    It is then showed why the laws of perspective indicate that she really spins counter-clockwise.

    Reply | Report Abuse | Link to this
  3. 3. Dolmance 01:42 PM 5/24/09

    Poor Bobby Jindal.

    Reply | Report Abuse | Link to this
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