Reinforcement: Learn It 1—Shaping

  • Define shaping
  • Understand the difference between primary and secondary reinforcers
  • Distinguish between interval reinforcement schedules
  • Distinguish between ratio reinforcement schedules

Shaping

In his operant conditioning experiments, Skinner often used an approach called shaping.

shaping

Instead of rewarding only the target behavior, in shaping, we reward successive approximations of a target behavior. Why is shaping needed? Remember that in order for reinforcement to work, the organism must first display the behavior. Shaping is needed because it is extremely unlikely that an organism will display anything but the simplest of behaviors spontaneously. In shaping, behaviors are broken down into many small, achievable steps. The specific steps used in the shaping process are the following:

  1. Reinforce any response that resembles the desired behavior.
  2. Then reinforce the response that more closely resembles the desired behavior. You will no longer reinforce the previously reinforced response.
  3. Next, begin to reinforce the response that even more closely resembles the desired behavior.
  4. Continue to reinforce closer and closer approximations of the desired behavior.
  5. Finally, only reinforce the desired behavior.

Shaping is often used in teaching a complex behavior or chain of behaviors. Skinner used shaping to teach pigeons not only such relatively simple behaviors as pecking a disk in a Skinner box, but also many unusual and entertaining behaviors, such as turning in circles, walking in figure eights, and even playing ping pong; the technique is commonly used by animal trainers today. An important part of shaping is stimulus discrimination. Recall Pavlov’s dogs—he trained them to respond to the tone of a bell, and not to similar tones or sounds. This discrimination is also important in operant conditioning and in shaping behavior.

Here is a brief video of Skinner’s pigeons playing ping pong.You can view the transcript for “BF Skinner Foundation – Pigeon Ping Pong Clip” here (opens in new window).

It’s easy to see how shaping is effective in teaching behaviors to animals, but how does shaping work with humans? Let’s consider parents whose goal is to have their children learn to clean their rooms. They use shaping to help them master steps toward the goal. Instead of performing the entire task, they set up these steps and reinforce each step. First, they clean up one toy. Second, they clean up five toys. Third, they choose whether to pick up ten toys or put his books and clothes away. Fourth, they clean up everything except two toys. Finally, they clean their entire room.