A creature's behavior is molded by circumstances both planned and happenstance. The two processes known as reinforcement and extinction interact to eliminate some behaviors and reinforce others.
Reinforcement is the indispensable condition for strengthening reactions. Its effect is exercised in the presence of all stimuli existent at the time it occurs. Some stimuli such as temperature, smell and momentary illumination may be irrelevant to reinforcing behavior, and are subsequently ignored in favor of more relevant stimuli. Eventually, a particular stimulus will be used to modify the behavior to the exclusion of other less relevant stimuli.
If all stimuli were used to create a new behavior, then energy would be wasted, time lost and the organism would have less of a chance of survival and opportunity to pass on its genes. On the other hand, the adaptability of behavior to critical stimuli depends on reducing the responses to noncritical stimuli. This decline in the strength of reaction by withholding reinforcement is known as extinction. It does not necessarily define a situation in which the response in a creature has been reduced to zero.
Many experiments have been carried out to modify behavior using the hypotheses of reinforcement and extinction. Although some of these studies have been successful, they have not led to entirely predictable results. The reason for this is that, like many other areas of human psychology, much depends on the individual.
For example, Pavlov carried out an experiment when which he stimulated a dog's skin and then fed it two minutes later. After the experiment was repeated several times, the dog salivated about two minutes after its skin was stimulated, even though it received no food. The conditioned stimulus in this case was not "skin stimulation," but "2-minute-old memory of past skin stimulation." This phenomenon, which is referred to as a memory reflex, can be established more readily in children than in animals.
In another experiment, a child who was afraid of rabbits was put in a room, together with a caged rabbit, while he eating. At the beginning of the experiment, the rabbit was placed at the far end of a long room; every day, it was brought slightly nearer to the child. Eventually, the child was able to play with the rabbit happily as he associated the rabbit with a happy stimulus like eating.
Krasnogorski performed another type of test on children. He trained a child to open his mouth to receive candy whenever a certain point on his arm was touched a few minutes after a bell had rung. Repeated touching of the arm without the bell, as well as hearing the bell alone, failed to produce the desired reaction. This reaction was labeled by Krasnogorski as storing and discharge, as it appeared that the stimulation from the bell was stored in the nervous system until the arm was touched, and then discharged in the form of the mouth reaction.
However, it is not entirely proven that behavior can always be reinforced and then removed on a whim. In another study, for example, college students were conditioned to a light and then a puff of air being blown on their cornea to make them blink. There were three different groups, one in which participants had 100 percent reinforcement in their trials, because a puff always followed the light; a second group that received 50 percent reinforcement; and then a group subjected to extinction trials.
This group had 100 percent reinforcement for the first set of trials, then a batch of 48 non-reinforced trials, and then 24 extinction trials. The results showed that non-reinforced trials do not always lead to behavior extinction. Furthermore, behavior is more likely to be reinforced over a longer-term experiment than a shorter-term one.
The researchers did conclude, however, that extinction of behavior is more likely to occur when the behavior is not always reinforced as vigorously. Overall, the reinforcement or extinction of behavior has little do with the number of times reinforcement or extinction occurs, instead relies heavily on the individual's inner strength.