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Why it makes your head spin
The optical illusion here is from coolopticalillusions.com. When you look at it, what do you see? Rotating spirals?
This is called an illusory movement or a peripheral drift illusion. It occurs by creating a repeating pattern, called sawtooth luminance gradients, which are used to create a movement sensation as your eyes move around the periphery of the image. If you were to keep your eyes focused at the center point of one of the spirals, it will remain fixed in its position.
The effect was first written about by Jocelyn Faubert and Andrew M. Herbert in their 1998 paper, “The peripheral drift illusion: A motion illusion in the visual periphery.” They assert that the primary cause of the effect is luminance, or the amount of light that can be seen by the eye based upon the angle of view. In this case, movement of the eyes shifts the brightness of the colors, which then results in the perception of a moving image. This effect is enhanced by the strong contrast between the black, yellow and blue rectangles.
These two elements, luminance and contrast, cause temporal differences that trick the brain’s motion system. So it’s really not your head that’s spinning; it’s your brain.
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