Gaze into these hypnotic rings and you'll be convinced that you're
staring at a spiral. But if you carefully follow their outline, it
becomes clear that they're actually concentric circles.
The animation, created by Douglas Reedy of Dublin, Ohio, is based on a static illusion developed by Baingio Pinna from the University of Sassari in Italy and Lothar Spillmann
from University Hospital Freiberg in Germany. The illusion is created
due to the tilt of tiny squares that make up the outline of each
circle. When they lean in opposite directions in alternating rings, a
spiral is perceived. Tweaking their angle of inclination creates a spiral with a different orientation.
The
squares in a circle also alternate in colour, which seems to intensify
the effect compared to the same pattern in a uniform colour. When the
squares are shifted upright, the illusion vanishes.
The effect is stronger at the edges of your gaze compared to the center, which gives insight into how it works. Alvin Raj from the Perceptual Science Group at MIT and his team have been investigating the phenomenon by testing a denser version of the illusion with more squares and rings.
Raj suggests that the way we size up the image in our peripheral vision
causes a calculation error that accounts for the perceived swirl.
"Some of the strange things you see
might be a by-product of your visual system losing some information and trying
to make the best of it," explains collaborator Benjamin Balas of North Dakota
State University.
If you enjoyed this illusion, see colours emerge from a spinning disc or watch how shifting lines can create a phantom
spin.
http://www.newscientist.com/
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