| Abstract: | Fear thresholds were measured in four experiments by exposing rats to electric shock in order to determine the maximal intensity rats would tolerate rather than enter a fear-arousing box and/or stop freezing. Increasing fear raised these thresholds. They were greater for rats having to escape shock to a fear-arousing box than for rats having to escape shock and fear to a neutral box. The forgetting functions for the latter two groups differed: the first group yielded a monotonic decay function, whereas the second group yielded an inverted U-shaped function. These thresholds decreased as a function of an avoidance learning procedure. Rats that had to escape shock to a fear arousing box did not do so immediately, although they had stopped freezing. An avoidance-avoidance conflict explanation for immobility was not found to be valid. A theoretical formulation based on the following two hypotheses was suggested to explain these results: the fear-aroused freezing (immobility) is an unlearned response; finding a way to escape the source of fear starts another unlearned response, withdrawal. |
