“There’s a famous experiment by Dan Simons and Christopher Chabris first carried out in 1999. The experiment involves a video of two teams passing basket balls back and forth. One team is dressed in black, the other team is dressed in white. The video lasts about two minutes, and the viewer is asked to count how many times the white team passes the ball. The teams are darting about, dodging in and out, circling and weaving, passing the balls between themselves. It’s hard to keep a track on the action, but you count the passes and confirm the result, which is then displayed on the screen at the end. After this you are asked to watch the film again, only this time you are told not to count the passes. It is only on the second viewing that you realise that in the midst of the action a man in a gorilla suit had walked determinedly across the basket ball court, stood still for a few seconds, beat his chest vigorously, and then walked off again.” (05/10/08)