In operant conditioning, reinforcement by means of a stimulus (7) that has acquired reinforcing properties by having been paired with a reinforcer. For example, if a bell is sounded repeatedly before an animal is fed, then the bell becomes a secondary reinforcer that can be used to reinforce a particular response, such as pressing a lever. Secondary reinforcement is especially useful in shaping (1), because it is often difficult to time primary reinforcers such as food sufficiently precisely. The counterpart of secondary reinforcement in classical conditioning is higher-order conditioning. secondary reinforcer n. A stimulus (7) that has become a reinforcer through secondary reinforcement.