PREFERENCE FOR SIGNALED OVER UNSIGNALED SHOCK SCHEDULES - RULING OUT ASYMMETRY AND RESPONSE FIXATION AS FACTORS

Experiment 1 tested whether a symmetrical choice precedure yields results different from those previously reported using the unidirectional standard changeover procedure. Subjects [rat] could change at any time from unsignaled to signaled shock by pressing a lever and from signaled to unsignaled shock by pressing a 2nd lever. Results were identical to those of the standard procedure and showed that the standard procedure is fully adequate. Experiment 2 tested whether choice of high density signaled shock over low-density unsignaled shock resulted from initial training with equal-density schedules. Subjects were trained and tested with signaled shock twice as dense as unsignaled shock. Subjects (3 of 4) strongly preferred the signaled condition, thus ruling out carry-over and response fixation as alternative explanations.