This is a classic illusion named after Ludimar Hermann who discovered it in 1870. At every point where the white lines intersect our eyes perceive a gray, shadowy blob. If you look directly at one of the intersections though, the blob disappears.
Stare at the image for about half a minute without moving your eyes and watch as it gradually disappears. This is a variation of Troxler’s effect which essentially says that if you fixate your eyes on a certain point, stimuli near that point will gradually fade.
The Kanizsa Triangle was named after the psychologist Gaetano Kanizsa who first described its effect. When you look at the image your brain creates contours (outlines) of a triangle although none exist. In reality it is an illusion created by the the wedges and the angles.
Found in virtually every psychology textbook in the world, the two monsters in this illusion are in fact the same size. Your brain automatically adjusts images that it perceives to be distant in order to compensate for the fact that they are larger than they seem.
First described by British psychologist James Fraser in 1908, this illusion is also known as the “false spiral”. While it appears that the overlapping arcs are spiralling into infinity they are in fact only a series of concentric circles.
Blue vs Green
Black on White
Although the two red lines seem to be bowed outwards they are perfectly straight and parallel. This illusion is attributed to Ewald Hering, a German physiologist who believed that the distortion was derived from the mind overestimating the angles at the points of intersection.
Also known as the Ebbinghaus Illusion, there is still a debate in psychological circles as to the exact mechanism and implication of this effect. Essentially, however, the orange circle on the left appears to be smaller than the one on the right although in reality they are the same size.