Book T of C
Chap T of C
If you signed up for a psychology class titled Conditioning and Learning or Animal Learning Laboratory, you might find yourself in a so-called "rat lab." Although many students start out with negative feelings about rats, they often end up enjoying such a class. Rats turn out to be friendly, intelligent creatures that often enjoy human company when tamed. Many a retired rat lab rodent has lived out its life as a human pet. During its working life in the lab, the rat serves as an ideal subject for studying learning under controlled conditions.
What are typical features of an operant chamber?
The operant chamber or Skinner Box for a rat
Often the first thing students do in a rat lab is handle the rat. This helps the rat become accustomed to human contact and not be too anxious to perform during future experimental sessions.
The next task might be to observe the rat in the operant chamber, a little cage where conditioning takes place. A typical operant chamber is shown here. Researchers can put a light or buzzer on the wall, or dispense food pellets one at a time from the automated dispenser.
A lever (labeled bar) sticks out of the wall of the operant chamber. This is the switch that the rat learns to press to get food. The food might be Purina Rat Chow or some other commercial rat food formed into little pellets that can be dispensed automatically.
What are early activities of students in a rat lab?
If you are a student just starting out to learn about operant conditioning, you may be asked to watch a rat in the operant chamber and write down all its behaviors for fifteen minutes. If the rat presses the bar, you make a note of it. The rat may not press the bar at all, or it may press the bar a few times. The unreinforced rate of response is the baseline level of responding.
Next comes a procedure called magazine training. ("Magazine" in this context means "storage area.") Each cage has a food cup, the magazine, where food pellets are delivered. The researcher can press a button on a remote control unit to deliver a food pellet at any time. To teach the rat where this food is delivered, a student can moisten a few pellets of food to increase their odor, rub them on the hopper, and leave a few pellets in the hopper. The rat, if deprived of food overnight, will go toward the odor of the moistened pellet, find the pellets in the hopper, and consume them.
What does a rat learn during magazine training?
Now the rat knows where to find food. After the food is consumed, the rat starts exploring the cage looking for more food. The student in the rat lab waits until the rat is near the food magazine, preferably facing it. Then the student presses a remote control button that causes a dry food pellet to drop into the metal dish with a clattering sound.
The rat quickly learns that a certain stimulus (the sound of a dry food pellet clattering into a bowl) can be followed by a response (running to the food hopper) that will be reinforced (followed by a stimulus, in this case food, which makes the behavior more frequent in the future). So far, the only behavior that has been reinforced is running toward the food bowl.
What is shaping?
Now a student might start an operant conditioning procedure called shaping, also called handshaping and the method of successive approximations. Shaping is a way to get an animal to perform a new behavior. The behavior that the animal is supposed to learn is called target behavior. In an operant conditioning laboratory using rats, the first target behavior after magazine training is likely to be the bar-press, which is the act of pushing down a little rounded metal bar that protrudes from the side of the operant chamber.
How is a rat shaped to press the bar?
The method of successive approximations or shaping consists of reinforcing small steps toward the target behavior. First the student gives the rat a food pellet when it is anywhere near the little metal bar. The rat learns this and soon it stays near the bar. Then the rat may be required to touch the bar before it receives a food pellet. (It is likely to touch the bar at some point, if it is hungry and exploring.) Finally, it is required to press the bar to receive a food pellet. This process of reinforcing gradual changes in behavior is shaping or the method of successive approximations. We will discuss shaping more in the later section on applied behavior analysis.
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Copyright © 2007 Russ Dewey