The term Beta movement is an optical illusion whereby viewing a rapidly changing series of static images creates the illusion of a smoothly flowing scene. This occurs when the frame rate is greater than 10 to 12 separate images per second. The illusion of motion caused by animation and film relies on beta movement. The static images do not physically change but give the appearance of motion because of being rapidly changed faster than the eye can see. This optical illusion is caused by the fact that the human optic nerve responds to changes in light at about 10 cycles per second, so changes about double of this are registered as motion instead of being separate distinct images.