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The Spinning Siren - a perceptual brain teaser

  1. Dec 10, 2009 #1
    The trick is to see this lady spinning in each direction: clockwise or counterclockwise. Most will see it orienting in one direction only. It's difficult to switch it in our minds. For many the task will be impossible.

  2. jcsd
  3. Dec 11, 2009 #2
    Okay assuming it's not just a simple case of switching the direction of the spin ever so often, I reckon it's probably just a matter of two things being slightly out of sinc, either the frequency of spin of the lady and her shadow, or a difference in strength between the muscles in your right and left eye.
  4. Dec 11, 2009 #3
    The image is an animated GIF with only 34 frames, so it's not switching (although there does seem to be a slight hiccup between the 34th and 1st frame).

    I'm not sure what you mean-- if that were true, wouldn't you expect to see one version if you closed your left eye, and another version if you closed your right eye?

  5. Dec 11, 2009 #4
    A three dimensional skater can turn clockwise or counter-clockwise. However this skater is two dimensional. The direction she turns in is determined not by your eyes, for they can only see a two dimensional image, but by your brain. Imagine, instead of a human figure, an oblique line sweeping out a cone with the lower endpoint stationary. Now make a two dimensional flip book image of it. In the flip book, the upper endpoint will trace a line going alternately 'left to right' and 'right to left' in a plane. There is no question of clockwise or counter-clockwise there. Would the same illusion occur?
  6. Dec 11, 2009 #5
    I think it would have something to do with one eye seeing her foot lets say, arrive slightly later on the right than the other eye does and your brain quickly switching between using (the information from) your dominant eye and the other eye when your dominant eye gets tired, so you would need to look through both eyes to get the effect.

    I'm really just guessing here, but my feeling is that it would be a similar effect to what would happen when you watch a spinning wheel for a long time, after a while it looks like the spokes are rotating backwards. I'm guessing there would be an analogous effect for any such periodic motion where you're watching it for a decent amount of time. Of course if you still see the effect looking through only one eye that would blow that theory out of the water :)
    Last edited: Dec 11, 2009
  7. Dec 11, 2009 #6


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    I can mentally flip her direction of rotation pretty much at will - just don't "buy in" to the first direction your brain perceives, and that should help.
  8. Dec 11, 2009 #7
    Okay just saw it switch looking through just one eye ;) so that theory is bogus. I seem to find it easier to switch the rotation when I look at her foot and the shadow of her foot at the same time, I cant help wondering if the shadow is playing some part here? Perhaps in simplifying the image in my mind to something similar to what you describe jimmysynder.
    Last edited: Dec 11, 2009
  9. Dec 17, 2009 #8
    This "illusion" is also flawed due to the shadow in the forefront, moving right to left, which would be moving in the opposite direction if she were even able to spin counter-clockwise.

    The only way the acclaimed "left brain" would be able to see her spinning CCW is if they ignored available information.

    Placing my hand over the shadow, I can indeed see her spinning CCW. But, sorry, my makes use of all available info, so, given the visual information provided in the "illusion," she's spinning CW.
  10. Dec 29, 2009 #9
    If I cover up the silhouette and just look at the shadow underneath then look at her, I see her spinning CCW. If I cover up the entire silhouette and shadow except for the right side of the picture so that you can only see her arm poke in and out, I see her going CW.

    I think that it's just fine. When seeing her go CCW, your brain thinks the shadow is caused because she becomes closer to the ground, which causes the shadow to come into view.
  11. Jan 10, 2010 #10
    If you put your fingers over the body part and just look at the top of the head and shadow part, in my view the head is going a different way than the feet...
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