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By David Ponce
Look at the red dot. Then look at the green dot. Notice something? If your eyes are working right, you should notice the rotation of the rings change directions every time. This illusion uses the fact that vision is different at the fovea (the center of the retina and point of sharpest vision) and at the periphery. Here comes the science:
There are two sources of information.
The global motion rotates counter-clockwise; the internal motion rotates clockwise.
Your visual system has to “choose” how to perceive these conflicting sources of information. In other words, will perception be guided by the motion of the ovals? Or by the motion of the internal lines? Or by a combination of these two? Or will you be able to see both types of motion at the same time, while keeping their signals separate?
When you look directly at the one-ring display, you can discern both sources of information (the ring will spin one way, and the motion caused by the internal lines goes the other way). But when you look at this display peripherally, it becomes difficult to separate the two sources of information, and the internal motion drives the perceived direction of the ring.
We hypothesized that the machinery of the foveal visual system allows us to represent multiple features simultaneously, but this machinery is absent in the periphery. The peripheral visual system seems to mix up the features that are available in the scene.
The above illusion is the courtesy of Arthur Shapiro, Associate Professor, Department of Psychology, American University in Washington DC.
VIA [ Illusions Sciences ]