Figure 4.10: B. F. Skinner and his operant-conditioning chamber To study operant behavior in rats and other animals, Skinner invented an apparatus widely known as the Skinner box. When the rat shown here presses the lever, it activates an electrical relay system that causes the delivery of a food pellet into a cup next to the lever. Each lever press can be automatically recorded to produce a cumulative record, such as that shown in Figure 4.10.

Time & Life Pictures/Getty Images