<P> The trainer starts by reinforcing all behaviors in the first category, here turning toward the lever . When the animal regularly performs that response (turning), the trainer restricts reinforcement to responses in the second category (moving toward), then the third, and so on, progressing to each more accurate approximation as the animal learns the one currently reinforced . Thus, the response gradually approximates the desired behavior until finally the target response (lever pressing) is established . At first the rat is not likely to press the lever; in the end it presses rapidly . </P> <P> Shaping sometimes fails . An oft - cited example is an attempt by Marian and Keller Breland (students of B.F. Skinner) to shape a pig and a raccoon to deposit a coin in a piggy bank, using food as the reinforcer . Instead of learning to deposit the coin, the pig began to root it into the ground, and the raccoon "washed" and rubbed the coins together . That is, the animals treated the coin the same way that they treated food items that they were preparing to eat, referred to as "food - getting" behaviors . In the case of the raccoon, it was able to learn to deposit one coin into the box to gain a food reward, but when the contingencies were changed such that two coins were required to gain the reward, the raccoon could not learn the new, more complex rule . After what could be characterized as expressions of frustration, the raccoon resorts to basic "food - getting" behaviors common to its species . These results show a limitation in the raccoon's cognitive capacity to even conceive of the possibility that two coins could be exchanged for food, irrespective of existing auto - shaping contingencies . Since the Breland's observations were reported many other examples of untrained responses to natural stimuli have been reported; in many contexts, the stimuli are called "sign stimuli", and the related behaviors are called "sign tracking". </P> <P> Shaping is used in training operant responses in lab animals, and in applied behavior analysis to change human or animal behaviors considered to be maladaptive or dysfunctional . It also plays an important role in commercial animal training . Shaping assists in "discrimination", which is the ability to tell the difference between stimuli that are and are not reinforced, and in "generalization", which is the application of a response learned in one situation to a different but similar situation . </P> <P> Shaping can also be used in a rehabilitation center . For example, training on parallel bars can approximate walking with a walker . Or shaping can teach patients how to increase the time between bathroom visits . </P>

What is an example of shaping in psychology