Waterfall Effect (Rotating Spirals)
Illusory motion, its direction, and afterimages.
As the disc spins, the spiral patterns seem to turn inside out. Then, after focusing on the patterns for a while, looking at a stationary object reveals a surprise: the object appears to move – in the opposite direction!
Seeing, or perceiving, begins on the retina of the eyes but mainly happens in the brain. That’s why we experience such surprises. Focus on the spinning spiral with one eye, cover it, then observe the stationary object with the other eye.
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