IT IS an illusion that has bedazzled people since Aristotle described it 2000 years ago. If you look at a waterfall for a short time, then look at the bank beside it, the bank will appear to drift upwards. Now an experiment that monitors brain activity has explained how the “waterfall effect” arises.
It confirms a hypothesis proposed in the 19th century by the German psychologist Sigmund Exner. He said the waterfall illusion was caused by neurons tuned to opposite directions of motion. While watching a waterfall, the brain cells that detect downward motion become tired. When the eyes look…
