Wednesday, May 25, 2011

The Magic or Impossible Triangle

You're probably familiar with the Penrose triangle, an impossible object that can't exist in ordinary 3D space, and the Kanizsa triangle, an illusion that makes a triangular shape appear thanks to carefully-placed fragments. Now Christopher Tyler from the Smith-Kettlewell Institute in San Francisco has creatively combined the two brain tricks in an animation to produce a dual effect.

In the video above, the inner markings of an impossible triangle appear first. With the twirl of an animated magic wand, you start to see the full shape as the spinning stick induces illusory contours.

Then three red spheres appear, reminiscent of the circles in Kanizsa's famous trick, moving across the screen in different ways to infer contours once again. Finally, the balls settle into the corners of the triangle, superimposing the two classic illusions and creating the most pronounced combination of the two effects.

According to Tyler, depth processing, which occurs in the occipital lobe of the brain, helps us perceive the impossible triangle. Since the shape displays conflicting orientations, our brain picks one of these possible realities and switches between them. The triangle at the end of the video appears thanks to illusory contours, which are created as our brain choosees the most likely configuration given the visual information provided.

The illusion was short-listed at the Best Illusion of the Year Contest which took place last week in Naples, Florida. You can see the other winning illusions here.

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