Classical And Operant Conditioning
The systematic study of conditioning began with the Russian physiologist Ivan P. Pavlov. Working in the late 1800s, Pavlov developed the general procedures and terminology for studying classical conditioning wherein he could reliably and objectively study the conditioning of reflexes to various environmental stimuli.
Pavlov initially used a procedure wherein every few minutes a hungry dog was given dry meat powder that was consistently paired with a bell tone. The meat powder always elicited salivation, and after a few experimental trials the bell tone alone was able to elicit salivation. In Pavlov's terminology, the meat powder is an unconditional stimulus because it reliably or unconditionally led to salivation. The salivation caused by the meat powder is an unconditional response because it did not have to be trained or conditioned. The bell tone is a conditional stimulus because it was unable to elicit salivation until it had been conditioned to do so through repeated pairings with the unconditional stimulus. The salivation that eventually occurred to the conditional stimulus alone (the bell tone) is now called a conditional response. Conditional responses are distinctly different from unconditional responses even though they are superficially the same behavior. Conditioning is said to have occurred when the conditional stimulus will reliably elicit the conditional response, or when reflexive behaviors have come under the control of a novel stimulus.
In line with his physiological orientation, Pavlov interpreted his findings according to his hypotheses about brain functioning. He believed that organism responses are determined by the interaction of excitatory and inhibitory processes in the brain's cerebral hemispheres.
There are a number of different classical conditioning experimental designs. Besides varying the nature of the unconditional stimulus, many involve varying the timing of the presentation of the stimuli. Another type of experiment involves training a subject to respond to one conditional stimulus and not to any other stimuli. When this occurs it is called discrimination.
American psychologist Edward L. Thorndike developed the general procedures for studying operant conditioning (also referred to as instrumental conditioning) in the late 1800s. Thorndike's experimental procedure typically involved placing cats inside specially designed boxes from which they could escape and obtain food located outside only by performing a specific behavior such as pulling on a string. Thorndike timed how long it took individual cats to gain release from the box over a number of experimental trials and observed that the cats behaved aimlessly at first until they seemed to discover the correct response as if by accident. Over repeated trials the cats began to quickly and economically execute the correct response within just seconds. It seemed the initially random behaviors leading to release had become strengthened or reinforced by their positive consequences. It was also found that responses decreased and might eventually cease altogether when the food reward or reinforcement was no longer given. This is called extinction.
In the 1930s and 1940s, the American psychologist Burrhus F. Skinner modified Thorndike's procedures by, for instance, altering the box so that food could be delivered automatically. In this way the probability and rate of responding could be measured over long periods of time without needing to handle the animal. Initially, Skinner worked with rats but he eventually altered the box for use with pigeons.
In these procedures the response being conditioned, pressing the lever, is called the operant because it operates on the environment. The food reward or any consequence that strengthens a behavior is termed a reinforcer of conditioning. In operant conditioning theory, behaviors cease or are maintained by their consequences for the organism (Thorndike's "Law of Effect").
In most operant conditioning experiments, a small number of subjects are observed over a long period of time, and the dependent variable is the response rate in a given period of time. In traditional operant conditioning theory, physiological or biological factors are not used to explain behavior as they are in traditional classical conditioning theory.
Variations in operant conditioning experimental designs involve the nature of the reinforcement and the timing or scheduling of the reinforcers with respect to the targeted response. Reinforcement is a term used to refer to the procedure of removing or presenting negative or positive reinforcers to maintain or increase the likelihood of a response. Negative reinforcers are stimuli whose removal, when made contingent upon a response, will increase the likelihood of that response. Negative reinforcers then are unpleasant in some way, and they can range from uncomfortable physical sensations or interpersonal situations, to severe physical distress. Turning off one's alarm clock can be seen as a negative reinforcer for getting out of bed, assuming one finds the alarm unpleasant. Positive reinforcers are stimuli that increase the likelihood of a response when its presentation is made contingent upon that response. Giving someone pizza for achieving good grades is using pizza as a positive reinforcer for the desired behavior of achieving good grades (assuming the individual likes pizza). Punishment involves using aversive stimuli to decrease the occurrence of a response.
Reinforcement schedules are the timing and patterning of reinforcement presentation with respect to the response. Reinforcement may be scheduled in numerous ways, and because the schedule can affect the behavior as much as the reinforcement itself, much research has looked at how various schedules affect targeted behaviors. Ratio and interval schedules are two types of schedules that have been studied extensively. In ratio schedules, reinforcers are presented based on the number of responses made. In interval schedules, reinforcements are presented based on the length of time between reinforcements. Thus the first response to occur after a given time interval from the last reinforcement will be reinforced.
Conditioning and theory thrived from approximately the 1940s through the 1960s, and many psychologists viewed the learning theories based upon conditioning as one of psychology's most important contributions to the understanding of behavior. Psychologists created numerous variations on the basic experimental designs and adapted them for use with humans as well.