2. Negative Reinforcer:
A negative reinforcer is a stimulus or event when its cessation or termination is contingent upon a response, increases the likelihood that the response will occur again.
3. Primary Reinforcer:
Primary reinforcer is one that is effective for an untrained subject. It does not require any special previous training in order to strengthen behaviour. The first time a primary reinforcer is made contingent upon a response, it will begin to strengthen that response. For example, a food for a hungry organism and a water for a thirsty organism.
4. Secondary Reinforcer:
Secondary reinforcer, unlike the primary reinforcer, does not work naturally. For it to become effective the learner must have had experience with it. For this reason secondary reinforcers are called as learned or conditioned reinforcers or responses. Stimuli become secondary reinforcers in operant conditioning by being paired with the primary reinforcers.