Optical Illusions are Fun

An animation that appears to have illusory contours was awarded second place in the contest. Created by Bart Anderson at the University of Sydney, Australia, it's made up of four circles and four dots that move back and forth over the outline of a rectangle. Contours connecting the moving dots in the middle seem to appear, creating a diamond that sometimes seems to morph into a more rounded shape as it stretches out.

Contours appear in many illusions. They can normally be explained by the way fragments of objects are arranged: a well-known shape without visible contours is inferred because our brains choose the most likely configuration based on the visual information.

But this explanation doesn't seem to apply to Anderson's illusion. The moving circles and dots are never partially obscured, so the brain shouldn't have to infer another shape. "This illusion can't be understood with any known mechanism that has been proposed to explain the formation of illusory contours," says Anderson.