Reinforcing successive approximations

{{ExpPsy} The concept of reinforcing successive approximations, or more commonly, shaping is a psychological concept used primarily in behavioral psychology. It was introduced by B.F. Skinner, whom many regard as the father of behavioral psychology. In many textbooks, shaping is formally defined as reinforcement of successive approximations to the terminal goal. The principles of shaping are present in everyday actions. Essentially, shaping is used when giving instruction (such as "touch the bar for food") is impossible (by a lack of language or communication).

The successive approximations reinforced are increasingly accurate approximations of a response desired by a trainer. As training progresses the trainer stops reinforcing the less accurate approximations. For example, in training a rat to press a lever, the following successive approximations might be reinforced.


 * 1) simply turning toward the lever will be reinforced
 * 2) only stepping toward the lever will be reinforced
 * 3) only moving to within a specified distance from the lever will be reinforced
 * 4) only touching the lever with any part of the body, such as the nose, will be reinforced
 * 5) only touching the lever with a specified paw will be reinforced
 * 6) only depressing the lever partially with the specified paw will be reinforced
 * 7) only depressing the lever completely with the specified paw will be reinforced

The trainer would start by reinforcing all behaviors in the first category, then restrict reinforcement to responses in the second category, and then progressively restrict reinforcement to each successive, more accurate approximation. As training progresses, the response reinforced becomes progressively more like the desired behavior.

The culmination of the process is that the response strength of lever-pressing increases. In the beginning, there is little probability that the rat will depress the lever, the only possibility being that it will depress the lever by accident. Through training the rat can be brought to depress the lever frequently.

Successive approximation are not the same as feedback processes, which increase the accuracy of a response without changing response strength. For example, a music student may tune a saxophone by playing successive notes into the microphone of an electroninc tuning device, each time adjusting the length of the saxophone until the tuning device says the note is on tune. This procedure, however, does not increase the probability that the student will continue playing the instrument or reduce the time the student requires to tune the instrument.

Practical Applications in Psychology and the Outside World
Shaping is used in two areas in psychology: training operant responses in lab animals, and in applied behavior analysis or behavior modification to change human or animal behavious considered to be maladaptive or dysfunctional. It also plays an impotant role in commercial animal training.