Watch the following clip. Does Rocky the yellow jacket (the University of Rochester mascot) appear to be expanding? It’s actually completely still. Our brains perceive that outward motion because it’s in the opposite direction of the inward moving lines.
According to research by Duje Tadin and his colleagues from the University of Rochester and from McGill University, as little as 25 milliseconds will trigger this illusion, known as the motion aftereffect. Even after the most fleeting exposure to movement, neurons in the motion center of the brain respond to stationary objects as if they too were in motion.
Because there is virtually always some background movement in our visual field, the authors expect this phenomenon to occur almost continuously. Their next goal is to figure out what if any advantage this might provide.