In this geometrical-optical illusion, discovered by the German physiologist Ewald Hering in 1861, two straight and parallel lines look as if they bow outwards. Hering ascribed the effect to our brains overestimating the angle made at the points of intersection between the radiating lines and the red ones. But why do we miscalculate?
Researcher Mark Changizi of Rensselaer Polytechnic Institute in New York believes it has to do with the human tendency to visually predict the near future. Because there's a lag between the time that light hits the retina and the time when the brain perceives that light, Changizi thinks the human visual system has evolved to compensate for the neural delay by generating images of what will occur one-tenth of a second into the future. He explained the Hering illusion in a 2008 article:
"Evolution has seen to it that geometric drawings like this elicit in us premonitions of the near future. The converging lines toward a vanishing point (the spokes) are cues that trick our brains into thinking we are moving forward as we would in the real world, where the door frame (a pair of vertical lines) seems to bow out as we move through it and we try to perceive what that world will look like in the next instant."