Every scene splits into a figure, the thing being looked at, and a ground, the space it sits in front of. The Law of Figure-Ground is one of the original Gestalt principles, first demonstrated through reversible images where the same lines can be read as either a vase or two facing profiles depending on which region the eye assigns as the subject. The visual system cannot perceive figure and ground simultaneously as equally weighted. One has to recede for the other to come forward.