Ask children who playa lot of video games and they will tell you. Realistic video games and flight simulators induce a form of motion sickness, admits Hughes Electronics of Los Angeles, USA. Most lose the ability to perceive depth for a time after they leave the simulator, and later see flashbacks that often make them sick. This happens because the focus of the pilot's eye drifts away from the screen when aircraft appear to be moving towards or away from them. To cure this, the company generates an image of another aircraft moving in the opposite direction. The compet- ing movements keep the pilot's eyes at the correct convergence angle, preventing the false perceptions of depth that cause sickness.