Learning to avoid an unpleasant or painful stimulus by responding to a warning signal.In the course of our lives we acquire many avoidance responses. Most of them, like keeping our hands away from fire or staying out of drafts, are highly useful. Others, such as running at the sight of a mouse, are unnecessary or exaggerated. Once they are learned, reactions of this kind tend to stay with us for the remainder of our lives. But the question is, how do we acquire them and Why are they so persistent? Psychologists have looked for answers to these questions primarily in experiments on animals. A typical laboratory apparatus consists of an enclosure with two compartments and a low fence between them. A dog is placed in one of the compartments and a buzzer is sounded for ten seconds. If the dog remains in the compartment for the full ten seconds, he receives an electric shock through a floor grill until he jumps over the fence to the other compartment. If he jumps during the ten seconds that the buzzer sounds, he does not receive the shock. In one series of experiments, Solomon and Wynne (1954) found that the dog does not jump to avoid the shock during the early trials. However, he soon begins to yelp not only when he receives the shock, but as soon as he hears the buzzer sound. A little later he becomes increasingly agitated when he receives the shock, and scurries around in an apparently aimless way. Then, during his scurrying, he happens to jump over the barrier and gets away from the shock. This brings him to a stage of learning called escape learning, for it takes only about ten trials for him to learn to jump the fence within three seconds after the onset of the shock. Finally, he learns to jump while the buzzer is on and before the shock begins. This is termed avoidance learning, and once it is established, the animal rarely gets shocked again. But why are avoidance responses so persistent? The experiment suggeststhree reasons. First, the dog has received shocks after hearing the buzzer sound, and he therefore associates the two and comes to fear the buzzer. Second, this tie is strengthened by the fact that he occasionally makes a mistake and receives a shock even when he is performing well—and it has been found that “partial reinforcement” of this kind makes a response particularly resistant to extinction. Third, each time he makes the correct response he obtains relief from his conditioned fear response set in motion by the buzzer, and this further reinforces the avoidance response. Tests have shown that when a dog learns an avoidance response in this way, he will react to the buzzer thousands of times even when the shock is never again administered. See REINFORCEMENT. The key to this situation seems to be that the animal constantly relives his fear and makes his avoidance response before he has a chance to see if the situation is painful. In fact, by avoiding the response, he never permits himself to find out if it is still dangerous. This helps to explain why childhood fears are so lasting. The child who has had a frightening experience in a swimming pool or lake will associate water with fear, and each time someone suggests going swimming his fear reaction will be evoked and the strength of his avoidance response will increase. Therefore he never gives himself a chance to test out the situation to see if it is still dangerous. What is more, his fear may “generalize” and he may avoid anything that has to do with swimming, including beaches, bathing suits or even stories about swimmers.