Effect of Discriminative Cues and Time Interval on Tolerance of Pain as a Measure of Fear

Abstract

In two experiments fear thresholds were measured in a modified shuttle box. Rats were exposed to electric shock in the left box to determine the maximal intensity they would tolerate rather than stop freezing (freezing threshold) and cross over to the right fear-arousing box (crossing threshold). Changing the surface color of the right box, in at least one of the experimental procedures, tended to reduce these thresholds. When thresholds were measured immediately after the fear conditioning stage, the crossing thresholds generalization curve tended to be steeper than the freezing threshold curve. If threshold measurements were taken 24 hr. later, the crossing thresholds generalization gradients were flattened. Rats which had to enter the right fear-arousing box to escape shock did not do so immediately, although they had already stopped freezing. These results were interpreted as consistent with the hypothesis that fear arouses freezing while finding a way to escape the source of fear arouses withdrawal.