Image: Mark Changizi, RPI
Look at the image above: the red lines are completely straight, but if you stare into the central (vanishing) point, then they appear to curve outward. Now, researcher Mark Changizi of the Rensselaer Polytechnic Institute in New York has discovered the secret to not only this optical illusion, but many other optical illusions: it's because the brain sees into the future!
When light hits your retina, about one-tenth of a second goes by before the brain translates the signal into a visual perception of the world. Scientists already knew about the lag, yet they have debated over exactly how we compensate, with one school of thought proposing our motor system somehow modifies our movements to offset the delay.
Changizi now says it's our visual system that has evolved to compensate for neural delays, generating images of what will occur one-tenth of a second into the future. That foresight keeps our view of the world in the present. It gives you enough heads up to catch a fly ball (instead of getting socked in the face) and maneuver smoothly through a crowd.
That same seer ability can explain a range of optical illusions, Changizi found. "Illusions occur when our brains attempt to perceive the future, and those perceptions don't match reality," Changizi said.
Here's how the foresight theory could explain the most common visual illusions — geometric illusions that involve shapes: Something called the Hering illusion, for instance, looks like bike spokes around a central point, with vertical lines on either side of this central, so-called vanishing point. The illusion tricks us into thinking we are moving forward, and thus, switches on our future-seeing abilities. Since we aren't actually moving and the figure is static, we misperceive the straight lines as curved ones.