Study 3 Pavlovian Conditioning

Our third study is based on the second of these viewpoints. It is patterned after an early experiment by Sheffield and Campbell (1954), and a later one by Holland (1977). In this preparation, food serves as the unconditioned stimulus. The conditioned response is the animal's activity during a signal for food delivery. In their experiment, Sheffield and Campbell found that conditioned activity increased substantially as a result of pairing the CS with the delivery of food.

Holland's contribution was to show that the activity measures exhibited a pronounced interaction with the modality of the CS. In an earlier experiment, Holland had obtained good activity conditioning when tone was the CS, but poor conditioning when light was the CS. In his 1977 experiment, Holland demonstrated that this pattern was due to the fact that the two types of stimuli controlled very different behaviours.

In this study, we will use Sheffield's paradigm to study the acquisition of a conditioned response. We will use tone and light stimuli, and examine the change in behaviour to the CS as a function of experience.

Apparatus. We will be using custom-constructed chambers to condition our animals. Each chamber will contain a small dish, through which we can deliver a food reinforcer. These pellets are 45mg pellets of food, manufactured by the P.J. Noyes company. In addition, each group will be provided with a switch-controlled light and tone.

Behavioural Measure. We will use the Sheffield procedure of recording bodily activity. Activity counts prior to the delivery of the CS will be compared to activity counts during the CS.

Procedure. Each rat will be run for a 90 minute session. During the first 26 minutes, you will train your rat to approach the food cup when a pellet has been delivered. Deliver a pellet by gently tapping the side of the chamber and rolling a pellet into the food cup. Try to keep your own movements as unobtrusive as possible, so that they do not become a signal themselves. Wait until the rat is next to the food cup, and deliver a pellet. Repeat this procedure until you are confident the rat will approach the cup whenever a pellet is delivered. Then wait until the 26 minutes has elapsed.

Following the 26 minute "magazine training" we will deliver 16 trials of the light and 16 trials of the tone. One will be followed by food delivery (the CS+) and the other will not (the CS-). Each stimulus will be presented for 10 seconds. Record for each stimulus presentation the amount of behaviour (i.e., number of contacts from the activity platform) in the ten seconds preceding the stimulus and the ten seconds during the stimulus. If your rat has an even number, follow the tone by a food pellet; if your rat has an odd number, follow the light by a food pellet. As in the magazine training phase, tap the side of the chamber just before presenting the pellet. Present a stimulus every two minutes, in the following order: LTLT TTLL LLTT LTTL LTTL LLTT LLTT LLTT. This is a random sequence constructed by presenting blocks of two lights and two tones with the order of light and tone randomized within a block. After the session, weigh and feed your rat.

To examine these questions, group your observations into blocks of four trials. Within each block, there are eight observations (two for each trial). Using the pre-stimulus and during-stimulus counts, compute the percentage with which the activity changed during a block, and plot this as a function of the four blocks for both stimuli. The format of this graph is up to you, but consider how to make the graph readable and informative.

Obtain the data from a team with the opposite relation between light and food and tone and food (i.e., if light was an CS+ for your rat, get the data from a team for which light was the CS-). Plot this rat in the same way.

Have you established evidence for learning of the CS-food relation? In particular, do you think our study provides a sufficient control for nonassociative effects? If there is a difference in learned behaviour controlled by light and tone CSs, what do you think may underlie it?

Rescorla, R.A. (1988). Pavlovian conditioning: It's not what you think. American Psychologist, 43, 151-160.

Schreurs, B.G. (1989). Classical conditioning of model systems: A behavioural review. Psychobiology, 17, 145-155.

Sheffield, F.D. & Campbell, B.A. (1954). The role of experience in the "spontaneous" activity of hungry rats. Journal of Comparative and Physiological Psychology, 47, 97-100.