Adaptation to the Drive Stimulus in Instrumental Escape Conditioning

Abstract

S~~nzmary.-In order to ascertain whether training conditions are complicated by adaptation effects in a water-escape situation rats ( N = 96) were exposed for 1 0 or 100 sec. to 15" or 32" C prior to each escape trial from a 15" C tank. Compared ro a non-exposed control condition over-all performance of the 15" C exposed groups was unaffected, bur the performance of the 32" C exposed groups was significantly ( p < .0005) enhanced. Adaptation effects which would lower the effective drive intensity in the escape situation, then, were not present, but prior exposure to a warmer condition did serve to increase the ecfective drive level. The absence of adaptation effects is related to similar findings with electric shock.The use of aversive stimuli for manipulating motivation and reward as well as punishment in basic learning research is increasing (Ch~uch, 1963;Woods, 1966". For the purpose of analyzing behavioral phenomena, stimuli of this class have many advantages over the complex internal states produced by the more traditional techniques of food and water deprivation. With external aversive stimuli, the conditions determining motivation and reward are under much greater control and can be more ~eadily specified. The level of motivation is concrolled by the intensity of [he aversive drive-stimulus, and reward magnitude is determined by the degree to which this drive-stimulus intensity is reduced. In escape conditioning, then, the motivational level can be readily reestablished on repeated occasions even with large rewards and massed trials, a condition which is totally impossible with the appetitive situation. Further advantages are that (1) magnitude of reward can be manipulated over a much greater range, ( 2 ) consummatory time is not confounded with magnitude of reward, ( 3 ) adapcation effects can be ascertained, and ( 4 ) the unconditioned response hierarchy can be determined so that learning effects can be assessed against a knowledge of initial response strength.The present paper addresses one of these points, that of the adapcation to the intensity of the drive-stimulus. So far repeated exposure to electric shock has been the major object of study (Miller, 1960;Karsh, 1963;Church, LoLordo, Overmier, Solomon, s: Turner, 1966), and the problem has never really been studied in appetitive conditioning although, with difficulty, it could be. When an animal is run over a number of days with, say, 22-hr. food deprivation or 85%