More about Shaping

Before you can reinforce a behavior, the behavior must occur. What if the behavior is not occurring? Then you must use a technique called shaping , mentioned earlier in connection with teaching a rat to press a bar in a Skinner Box.

What is the technical name for "shaping"?

Shaping is well described by its technical name: the method of successive approximations. To approximate something is to get close to it. To do successive approximations is to get closer by small steps. Shaping works by starting with whatever the organism can already do and reinforces closer and closer approximations to a goal.

Here are five simple rules for shaping.

What are five rules to observe, while using shaping?

1. Make sure the target behavior is realistic and biologically possible.

2. Specify the current (entering) behavior and desired (target) behavior.

3. Plan a small chain of behavioral changes leading from the entering behavior to the target behavior.

4. If a step proves too large, break it into smaller, more manageable steps.

5. Use reinforcers in small quantities, to avoid satiation (getting "full").

How are the five rules illustrated by teaching a dog to catch a Frisbee?

To illustrate the five rules, consider the task of teaching a dog to catch a Frisbee. If you have ever seen dogs catch a Frisbee, you know it is quite impressive. Suppose you want to teach your dog this trick. How do you do it?

According to rule #1, you have to decide whether your dog is physically capable of such an act. The national champion Frisbee-catching dogs are usually dogs like whippets with a lean, muscular build which permit them to leap high into the air to snatch Frisbees out of the breezes. Other breeds—bulldogs, Pekinese, and dachshunds—might be less able to learn this skill.

Suppose you have a dog that is physically capable of catching a Frisbee. Rule #2 says "specify the current (entering) behavior." This must be a behavior the dog can already perform. It should be a behavior that can be transformed, in small steps, into the target behavior. Frisbee catching requires that the dog take a Frisbee into its mouth, so you might start by reinforcing the dog for the entering behavior of holding the Frisbee in its mouth. Most dogs are capable of doing this without any training. In fact, they will gladly puncture a Frisbee with their canine teeth, so use a cheap Frisbee you do not mind ruining. The dog enters the experimental situation with this behavior already in its repertoire. That is why it is called an entering behavior.

Rule #3 says to devise a series of small steps leading from the entering behavior (holding the Frisbee in his mouth) to the target behavior (snatching the Frisbee from the air). Finding such a sequence of steps is the trickiest part of shaping. How can you get from "here" to "there"? One approach is to toss the Frisbee about a foot in the air toward the dog, hoping it will perform the skill so you can reinforce it. Unfortunately, this probably will not work. The dog does not know what to do when it sees the Frisbee coming, even if the dog has chewed on it in the past. It hits the dog on the nose and falls to the ground.

This brings us to rule #4. If a step is too large (such as going directly from chewing the Frisbee to snatching it out of the air) you must break it into smaller steps. In the Frisbee-catching project, a good way to start is to hold the Frisbee in the air. The dog will probably rise up on his hind legs to bite it. You let the dog grab it in his mouth, then you release it. That is a first, simple step. Next, you release the Frisbee a split second before the dog grabs it. If you are holding the Frisbee above the dog, you might drop it about an inch through the air, right into the dog's mouth.

Now the most critical part of the shaping procedure takes place. You gradually allow the Frisbee to fall a greater and greater distance before the dog bites it. You might start one inch above the dogs mouth, work up to two inches, then three, and so on, until finally the dog can grab the Frisbee when it falls a whole foot from your hand to the dog's mouth. (For literate dogs outside the U.S. and Britain, use centimeters and meters.) Keep rule #4 in mind; if the dog cannot grab the Frisbee when it falls 8 inches, you go back to 6 inches for a while, then work back to 8, then 10, then a foot.

Eventually, if the dog gets into the spirit of the game, you should be able to work up to longer distances. Once the dog is lunging for Frisbees that you flip toward it from a distance of a few feet, you are in business. From there to a full-fledged Frisbee retrieval is only a matter of degree.

Rule #5 says to have reinforcers available in small quantities to avoid satiation. Satiation (pronounced SAY-see-AY-shun) is "getting full" of a reinforcer—getting so much of it that the animal (or person) no longer wants it. If satiation occurs, you lose your reinforcer, and your behavior modification project grinds to a halt. Suppose you are using Dog Yummies to reinforce your Frisbee-catching dog. If you use 50 yummies getting it up to the point where it is catching a Frisbee that falls eight inches, you will probably not get much further that day. The dog is likely to decide it has enough Dog Yummies and crawl off to digest the food.

Why is satiation unlikely to be a problem in this situation?

Actually, dogs respond well to social reinforcement (praise and pats), and that never gets old to a loving dog, so dog trainers usually reserve their most powerful reinforcers for occasional use. Retrieval games are themselves reinforcing to many dogs. When I took a dog obedence course, the trainer used retrieval of a tennis ball to reinforce her dog at the end of a training session. That was a fine example of the Premack Principle in action because a preferred behavior (retrieving a tennis ball) was used to reinforce non-preferred behaviors (demonstrating obedience techniques).


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Copyright © 2007 Russ Dewey