How to Shape Behavior

In behavioral experiments, training animals to reliably perform the task is crucial to the success of the task. Still, finding ways to produce behaviors--no matter how simple--can prove challenging for any research scientist. Not to worry. Teaching animals to perform a desired behavior can be accomplished through a process called "shaping".  More specifically, shaping is a method for conditioning a behavior and was first introduced by B.F. Skinner.  The procedure involved gradually  changing behavior over time until a certain target behavior is reached.

This brings us to our first "rule" of shaping: Learning is a gradual process. This means that shaping a new behavior involves patience. One technique used to "patiently" shape behavior involves "successive approximations" of the target behavior.  The use of successive approximations involves reinforcing behaviors that come close to the target response without necessitating that a subject actually emit the target behavior.

One example of shaping might involve teaching a child to write his or her name. This might first involve praising the child only for correctly forming the first letter.  Eventually, in order to reach the goal of having he child write his/her full name, it becomes necessary to raise the bar until the child has written the second, third, and eventually all of the letters in the name. Importantly, successive approximations also allow for failure by only raising the bar a little at a time. Thus, the second rule of shaping is that learning involves making mistakes.  Certainly, it is just as important for an individual to learn what NOT to do as it for them to learn the desired behavior. To continue with the above mentioned example, it might be important for a child confusing the letters "M" and "N" to correctly learn to discriminate these letters in order to correctly spell his/her name.

A third rule of shaping is that reinforcement must be given in a consistent, steadfast manner.  When reinforcing approximations of a target behavior, it is important never to lower the bar once a behavior that is more proximal to the goal behavior has been learned. For example, it would not be effective to reward a child who had learned to spell half of their name for only inscribing the first letter. On the other hand, one must also be careful not to raise the bar too quickly. It is important to consistently reinforce each "step" in the approximation process for long enough to ensure that the subject has mastered the behavior before moving on.

The last major rule for shaping is that an experimenter must learn to observe behavior. To most rapidly shape an animal, an experimenter must exploit innate behaviors exhibited by that animal.  Realistically, an experimenter should take a naturally occurring behavior that best approximates the target behavior and begin to reinforce that behavior as an initial approximation. To do this, an experimenter MUST observe and understand an individual's behavior. The key word here is "individual", as no two animals will be shaped in the same manner. Thus, to shape a specific individual, one needs to have a well-developed understanding of the behavioral repertoire that an individual possesses. 

Shaping a lever response in an highly mobile rat might involve reinforcing moments when the rat's innate ambulations place the animal in close proximity to the lever. Once the animal has learned that the quadrant proximal to the response manipulandum is special, it would be easy to begin raising the bar and better approximating a lever response.  In contrast, a scared animal that freezes in the corner of the chamber could not be shaped using this same method (at least not easily).  As you might imagine, shaping this animal would necessitate a very different strategy.  One such strategy might be to spread pieces of food around the chamber so that our scared rat begins moving around to eat the food and better approximating our more mobile rat. 

Lastly, it is important to realize is that shaping takes practice. Practice allows you to observe animals behaviors, develop an understanding of individual differences among animals, and to develop a plan in your head for how to carry out your shaping procedure. Each subject is different, and each task we might ask a subject to complete comes with new challenges. Still, despite all of these differences, the essence of shaping never really changes. Happy shaping!

        David Barker