Neuropsychology Psychology 162, Fall 2008
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LEARNING AND SHAPING LABORATORY
Part 1: Shaping
The next laboratory will deal with learning. Learning is one of the most important functions of the nervous system. Since we are capable of learning, our nervous systems must be flexible to allow us to acquire behaviors that are best suited to the world (environment) that we happen to find ourselves in. Think of the ability to learn in this light: If you learn anything during a class period, you do not leave with the same nervous system with which you entered the room. In some way the nervous system must have changed to reflect what you have learned and any new behaviors that you may have acquired.
We will study learning by using one of the traditional techniques: operant conditioning. Operant conditioning is the procedure where behavior is controlled by what happens after the behavior; that is, its consequences. In other words what happens if an animal does X and is this result of behavior X desirable or not to the animal?
In the present laboratory, the behavior that is desired is having the rat press a bar and food will be delivered to the rat as the consequence. This consequence has been found to increase the frequency of bar pressing behavior and is therefore called reinforcement. A reinforcer is any stimulus that has the ability to increase the frequency of behavior. Because we give this stimulus to the animal and it increases the frequency of behavior we call it a positive reinforcer. If I remove a stimulus and the behavior increase, for example pressing a bar to turn off shock, then we call this a negative reinforcer. Note that to tell whether a stimulus or event is reinforcing or not, I look at the effect on behavior and not at the stimulus.
It is important to realize that rats are not born knowing that pressing a bar will lead to food or even that the bar can be pressed. In addition, rats do not have language so no amount of explanation or gesticulation on your part will enable the rat to press the bar. What the rat is endowed with is a set of behaviors that it has acquired through the complex biological and environmental factors working in concert. You use these behaviors and the conditioning techniques, explained below in the procedure section, to gradually condition the rat to press the bar. This technique of gradually conditioning the rat to press the bar is called shaping. Formally, shaping is called conditioning by successive approximations. This shaping portion of the laboratory is actually only preliminary to the main portion of the experiment, which is why there are four weeks assigned to this laboratory. We will discuss the next stage later.
Procedure For Shaping.
Prior to "running" your rat in the operant conditioning chamber you will need to deprive your rat of food for 24 hours (Check with me before you do deprivation of this length of time). You will also need to keep track of your rat's weight so the rat does not lose weight.
For the first part of the laboratory, each rat will be conditioned to a continuous reinforcement schedule (CRF). A CRF is when the rat receives one pellet of food for each bar press. Your task during this part of laboratory is to shape the rat to press the bar to obtain food. You as the experimenter will start our giving the rat food pellets for behaviors only remotely related to the bar press, e.g., turning towards the bar, and then gradually demand closer and closer behaviors to the bar press for a pellet until the rat begins pressing the bar on his own. It is important to be very consistent in what behavior the rat performs to get the food. In addition, timing is critical. If you are late in delivering the reinforcement, skip it. It will work better for the rat to miss a reinforcement than for the rat to get a reinforcement following the wrong behavior.
I recommend that two or three pellets of food be placed in the tray before you put the rat in the cage to start. The rat will go to the food. Then deliver another pellet while his head of the rat is in the tray getting the last pellet. There are two reasons for this first step. First, the rat will initially jump to the sound of the food dispenser. By repeatedly delivering food to the rat while his nose is in the tray the rat will habituate to the sound and will no longer jump. Second, an association will be formed between the sound and food and the sound will be able to operate as a secondary reinforcer. A secondary reinforcer is a stimulus that has the ability to increase the frequency of behavior through learning. Food is a primary reinforcer. It has the ability to increase the frequency of behavior without learning.
After the rat has habituated to the sound do not give food for putting its nose in the tray. The rat will begin to explore around. When the rat moves its head towards the tray, reinforce it. After this step make the rat rear up. Following these basic guidelines the rat will eventually press the bar, frequently by accident. Remember, these are recommendations that work for many rats. You must use the behaviors that your rat gives you. Your individual procedure for shaping your rat may be considerably different. The main question you need to ask is how you will know when the rat is conditioned? Your knowledge must be based upon some observable behavior or behaviors.
For this laboratory you will only be required to write up the method and results sections of a laboratory report. We will discuss these sections more as we proceed with the laboratory. However, one issue that needs to be addressed in the procedure subsection of the method section is how will you know that the rat has "learned" the bar press behavior. In other words, what are your criteria for stating that the rat has learned the behavior? I am leaving this question for you to answer. For next week, try to draft a section where you describe the laboratory procedures to shape the rat. This description should be general enough to apply to all of the rats in your lab section and specific enough that another person can evaluate your procedures.