Ace skepchick Rebecca Watson kindly sent me this great illusion….

Any ideas about why it works?


    1. It is important that there be a small line of neutral colour separating the lines. It needn’t be green, though. A mid-grey will also work.

  1. I think I get it, but it’s hard to explain…

    In the first figure, the black and white squares are arranged such that squares of a similar colour appear to form a wavelike curve. The eye (mind) wants to process the strung-together like-coloured squares as a curvy line. For these curves to be “true”, the mind then tricks itself into believing that some square edges are concave, and some convex… depending on their position in the “curve”.

    For this to be true, the outside edges of the curve appear (convex) longer , and the inside edges (concave) shorter. Therefore, the strips which have right-hand convex and left-hand concave-appearing edges are processed by the brain as being thinner on the left end, and the strips having left-hand convex and right-hand concave edges are processed by the brain as being thinner on the right end.

    The squares in the middle, or “neutral” part of the illusory “curve” appear normal, and the strips to which they belong appear to have parallel edges.

  2. I glimpsed Geoff’s “Café Wall Illusion” link… Didn’t read it all, but it mentions that the illusion does not work when the mortar is highly visible…

    This seems to support my theory, since the eye will not tend to process like colours as being grouped together on a curve if the squares are visible separate.

  3. I noticed that the strips remain ‘tapered’ until the squares are aligned even if there is a bit of space between them as they are being moved. Cool.

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    1. Paging Doctor Ponzi… these “guaranteed free gifts” typically are for people who get X number of friends to sign up for Y number of offers (which involve subscriptions to things, not-quite-free trials, etc).

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  5. the illusion is made by the fact that our eyes have different points of intercepting the image. let your eyes loose, and you will see to images of the same object. that why we se 3d, and thats why some one cane trick us .:)

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