First publised in New Scientist (March 4, 2011) by Catherine de Lange..☛..In the video above, you can see three versions of a new illusion by Sung Ho-Kim (☝) at Rutgers University, New Jersey, that trick your brain into thinking circular patterns that shift across a screen are actually spinning. Make sure you are close to the screen to see the full effect.
In the first animation, the top and bottom halves of the shape should look like they are rotating in opposite directions. They switch directions as the motion of the pattern changes from left to right. In the second version of the illusion, a block covers half of the shape. This time it looks like the spokes of a wheel are rotating as the whole pattern travels left and right across the screen. In the final animation, two gears connected by a chain appear to be rotating together. If you’re convinced that these shapes are actually turning, try tracking each of the short lines, and you’ll see that it’s an illusion. The physical trajectory of each line segment is purely horizontal and none of the circles are rotating.
Source: New Scientist