Experiments on habit reversal in the white rat following electro-convulsive treatment

Rats in a T-maze were taught two opposite habits successively, the first being heavily over learned compared to the second. One group of 14 rats was then given a series of 6 electroconvulsive shocks. The control group of 11 rats underwent a dummy procedure.

Tested subsequently the control group maintained the second habit but among the shocked animals some adopted the second habit and some the first. This was no evidence of habit reversal, however, for the behaviour of the shocked animals at the choice point was not distinguishable statistically from random behaviour.

The data of earlier workers are re-examined and, in all cases, animals said to have undergone habit reversal act as if at random.     

Cardiac conditioning in the white rat with food presentation as unconditional stimulus

Pavlovian conditioning of heart rate in the white rat was attempted using milk presentation as reinforcement, and with both trace and delay paradigms. Delay conditioning produced positive results that were statistically significant, whereas trace conditioning exhibited the same trends but did not reach statistical significance. In both cases, CR had the same direction as UCR to milk (acceleration of heart rate) and opposite to the unconditional reaction to CS. Extinction and reconditioning were both accomplished. Some indications of complex response interactions were noted in the occurrence of the cardiac CR on conditioning trials where the instrumental response to the UCS (drinking) eventually occurred, as against the absence of cardiac CR on trials where the instrumental response did not occur. The existence of such interactions was also indicated by the fact that CR on individual trials within any single session could vary in direction between acceleration and deceleration, although averages might be stable.     

Some effects of reward on the strength of position stereotypes in the white rat

Certain aspects of Maier's hypothesis that rigid behaviour stereotypes elicited in an insoluble problem situation are not explicable in terms of goal-motivated learning were tested thus: Forty-one white rats of Wistar stock were exposed to an insoluble problem in a water discrimination unit. Each of the twenty-four animals who formed position stereotypes was assigned to one of four groups. One of these groups served as a control and received no special treatment. Each of the remaining three experimental groups was given a different number of successively rewarded trials to the side of the stereotype. Finally, all groups were presented with a soluble problem, and the strengths of the stereotypes in each group observed in terms of the breaking of the stereotypes.

It was found that the strength of the stereotype behaviour was directly proportional to the number of rewarded trials. None of the stereotypes was sufficiently rigid to meet Maier's criterion of “fixated” response patterns. More stereotypes were formed by males than females. On the other hand no sex differences appeared in the subsequent behaviour of animals who did form stereotypes.

These results are interpreted as showing that stereotyped responses formed under conditions of the present experiment are not qualitatively different from learned responses.