Thesis

A comparison of the effect of moderate and strong shock on consummatory and instrumental behavior

A two part experiment was undertaken to compare the effects of punishment-shock on the consummatory response of eating and the instrumental response of bar pressing which led to food. The experiment was performed in order to test Solomon's prediction that a shock which suppressed eating would function as a discriminative stimulus and thus facilitate an instrumental response that led to food (Solomon, 1964). Two levels of shock were used. In the first part of the experiment, a shock which bad previously been shown to suppress eating in a group of 15 rats was made contingent upon the bar pressing response of another group of 15 rats. As in both groups were tested once a day for seven consecutive days, and the number of eating responses was compared with the number of bar presses over the seven trials. For the second part of the experiment, a shock which reduced but did not suppress responding (moderate shock) was used. The number of bar pressing responses and the number of eating responses of two groups of eight rats each were tested by means of a. counterbalanced design. That is, for half of the rats shock was first made contingent upon eating and then upon bar pressing. For the rest of the rats, shock was first made contingent upon bar pressing and then upon eating. This counterbalanced design was utilized to control for individual differences in reaction to moderate shock. This procedure was also utilized to control for any possible effects previous exposure to shock might have when the contingency was changed for the same S. Ss were tested once a day for 15 minutes on six consecutive days. Under strong shock there was no significant difference between the number of bar presses and the number of eating responses. However, on Trial 1, Ss made significantly more responses (bar pressing and eating) added together than they did on Trials 2 to 7, inclusive. Strong shock did not demonstrate any facilitatory properties. Under moderate shock, -Ss made significantly more eating responses than bar presses. Furthermore, the number of eating responses over successive trials was less variable and more stable than was bar pressing. Only when shock was moderate could it be shown to have facilitatory properties and thereby act as a discriminative stimulus. The present research did not support Solemon's prediction. Under strong shock bar pressing was suppressed as rapidly as was eating. However, under moderate shock it was shown that eating was less affected and more stable from trial to trial than was bar pressing. It was also shown that strong shock did not exhibit facilitatory properties. Only when the shock was moderate did it then demonstrate facilitatory properties and act as a discriminative stimulus.

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