Positive Reinforcement and Negative

Reinforcement as a theoretical concept in psychology can be traced back to Russian physiologist Ivan P. Pavlov and American psychologist Edward L. Thorndike, who both studied conditioning and learning in animals in the early 1900s. Pavlov developed the general procedures and terminology for studying what is now called classical conditioning. This term refers to both the experimental procedure and the type of learning that occurs within that procedure. Pavlov's experiments involved giving a hungry dog dry meat powder every few minutes. The presentation of the meat powder was consistently paired with a bell tone. The meat powder made the dog salivate, and after a few experimental trials, the bell tone alone was enough to elicit salivation.

In Pavlov's terminology, the meat powder was an unconditional stimulus, because it reliably (unconditionally) led to salivation. He called the salivation an unconditional response. The bell tone was a conditioned stimulus because the dog did not salivate in response to the bell until he had been conditioned to do so through repeated pairings with the meat powder. The salivation, thus, was a conditioned response.

Thorndike's experiments involved placing cats inside specially designed boxes from which they could escape and get food only if they performed a specific behavior such as pulling on a string loop or pressing a panel. Thorndike then timed how long it took individual cats to gain release from the box over a number of trials. Thorndike found that the cats behaved aimlessly at first until they seemed to discover by chance the correct response or responses. Over repeated trials the cats began to quickly and economically execute the correct response or responses within seconds. It seemed that the initially random behaviors leading to release were strengthened, or reinforced, as a result of the positive consequence of escaping the box and receiving food. Thorndike also found that responses decreased and in some cases ceased altogether when the food reward was no longer given.

Thorndike's procedures were greatly modified by Burrhus F. Skinner in the 1930s and 1940s. Skinner conditioned rats to press down a small lever to obtain a food reward. This type of procedure and the resultant conditioning have become known as operant conditioning. The term "operant" refers to a focus on behaviors that alter, or operate on, the environment. It is also referred to as instrumental conditioning because the behaviors are instrumental in bringing about reinforcement. The food reward or any consequence that strengthens a behavior is called a "reinforcer of conditioning." The decrease in response when the food or reinforcer was taken away is known as " extinction." In operant conditioning theory, behaviors cease or are maintained by their consequences for the organism.

Reinforcement takes on slightly different meanings in the two types of conditioning. In classical conditioning, reinforcement is the unconditioned stimulus delivered either simultaneously or just after the conditioned stimulus. Here, the unconditioned stimulus reinforces the association between the conditioned and unconditioned stimulus by strengthening that association. In operant conditioning, reinforcement simply serves to strengthen the response. Furthermore, in operant conditioning the reinforcer's presentation or withdrawal is contingent upon performance of the targeted response. In classical conditioning the reinforcement or unconditional stimulus occurs whether or not the targeted response is made.