B.F. Skinner (1904-1990) is regarded as one of the most influential psychologists of the twentieth century. He began his experiments on operant conditioning in the 1930s. Thorndike’s ‘puzzle box’ allowed the cat to learn the S-R connection in successive discrete trials.
Skinner wanted a better control over the learning situation, which allowed the organism to freely operate in its environment. To do all this, he invented Skinner box, which is also called the operant chamber. There is a device in the box, which can deliver food pellets into a tray at random. Inside the box, there is a lever which when pressed activates the device for delivering food pellets. A hungry rat is left inside the box. The rat exhibits random activities while exploring the box. Accidentally the rat presses the lever and a pellet of food is delivered. The first time it happens, the rat does not learn the connection between the response of lever pressing and food pellets. Sooner or later, the rat learns that the consequence of lever pressing is positive; lever pressing brings food.
The experimenter counts the number of lever presses. The number of responses within a particular unit of time is called the rate of response. Skinner used rate of response as a measure of learning. The rate of response is recorded and graphically shown by a cumulative recorder.
As rats are trained to press a lever, pigeons are trained to peck at a ‘key’ to produce positive consequence. Pecking the ‘key’ activates the mechanism of food delivery, which serves as a positive reinforcement. Since lever pressing and ‘key’ pecking responses are positively reinforced, they increase in frequency. The basic principle in operant conditioning is that the probability of occurrence of a particular response depends on the consequence of that response.
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The basic processes of classical conditioning that were discussed earlier holds good for the instrumental conditioning. After the rat has learnt to press the lever, we may dissociate food delivery (positive reinforcement) from the lever pressing response. If the rat now presses the lever, but does not get food, the response rate would gradually decrease, and finally disappear. The disappearance of response because of non-reinforcement is extinction. If a rest period is given, the response will reappear with a lowered strength, which is known as spontaneous recovery. Similarly, the phenomena of generalization and discrimination are also observed in operant conditioning.