Study 2: Habituation

January 20, 1997

Synopsis

Each rat will be placed in a chamber that can measure rapid movements. Sixteen puffs of air will be presented and the startle reaction to each puff will be measured. Of interest is the change in the intensity of this startle reaction over the sixteen presentations. Two additional "dishabituation" trials will be presented to determine if a change in the environment of the rat will reinstate the startle response.

Background

Habituation is a basic learning process exhibited by a number of different species. Although the paradigm itself is procedurally simple, it has been suggested that habituation may underlie a number of other learning phenomena. Indeed, Razran (1971) has suggested that the process responsible for habituation may be the basis of all other forms of learning.

Humphrey (1933) was one of the first to study the process of habituation. His procedure was very simple. He placed a number of snails on a glass plate. He would then give the plate a sharp jerk, which would cause the snails to withdraw reflexively into their shells. After each jerk, Humphrey would count the number of snails that had withdrawn. He found that, after several trials, the number showing the withdrawal response decreased. In other words, repeated stimulation of the withdrawal response resulted in a decreased tendency to withdraw.

Since Humphrey's study, a variety of techniques have been used to study habituation. A good review is provided by Thompson and Spencer (1966), who describe habituation in both behavioural and physiological preparations. Our own study will be modeled after work by Davis (1970), in which the startle response of a rat to a loud noise is studied for evidence of habituation.

Methodology

Subjects:

Our Sprague-Dawley rats will serve as the subjects.

Apparatus:

We will use three activity chambers, which are capable of measuring gross body movements by the rats. (This will mean that we will have to run several "shifts" to test all the rats.) We will be using a puff of air to elicit a startle reaction; straws will be provided.

Procedure:

The activity chambers are designed to measure large responses. These are counted by pulses on a counter, and will be used to measure the magnitude of the startle reaction.

The rats will be placed in the activity chambers for a 40 minute session. One minute after the start of the session, blow a moderate, but sharp, puff of air on the shoulder of the rat. (You should practice the procedure by blowing on your wrist until you are confident that you can deliver a reasonably constant air puff each time.) A total of 16 stimuli will be presented, with an interval of 2 minutes between each stimulus. For each stimulus, or trial, note the number of activity counts in the two seconds following each stimulus.

After the 16 habituation trials, we will try two dishabituation test trials. The dishabituation stimulus will be taking the rat out of his cage for 30 seconds. The rat will then be put back into the cage and two more stimuli will be presented.

After the session, weigh and feed your rat.

Results and Discussion Assignment

I would like you to plot the magnitude of the startle reaction of your rat over the 16 habituation trials. You may, if you think it will clarify the data, collapse your data into blocks of two trials or four trials. Also show the effects of dishabituation and consider how you could demonstrate a reliable dishabituation effect.

I would also like you to record the data of the other rats used in the same chamber as your rat and to graph an "average" habituation curve. Do you think the average curve represents a good depiction of the individual process?

References

Required:

Davis, M. (1970). Effects of interstimulus interval length and variability on startle-response habituation in the rat. Journal of Comparative and Physiological Psychology, 72, 177-192.

Thompson, R.F. & Spencer, W.A. (1966). Habituation: A model phenomenon for the study of neuronal substrates of behaviour. Psychological Review, 73, 16-43.