In 1981, "Scramble" was the first side-scroller with multiple, distinct levels. The art of the side-scrolling format was then greatly enhanced by parallax scrolling, which is used to give an illusion of depth. The background images are presented in multiple layers that scroll at different rates, thus objects closer to the horizon scroll slower than objects closer to the viewer. "Moon Patrol" is usually credited with introducing this feature in 1982, though Taito's "Jungle Hunt" also features parallax scrolling and was released the same year.