Regularity of Inescapable Shock Duration Affects Behavioral Topography, but not Shuttle Escape Performance

One purpose of the present experiment was to investigate the effects of exposure to fixed and variable duration inescapable shock on the subsequent acquisition of a shuttle escape response. Another purpose was to examine closely the behavior of animals during exposure to inescapable shock in an attempt to assess directly the behavioral changes occurring during this experience. Competing response accounts of the learned helplessness effect propose the mechanism of adventitious reinforcement during inescapable shock for the learning of low activity responses. Exposure to inescapable fixed duration shock should therefore be more effective than variable duration shock of the same average value in producing subsequent escape deficits. However, the present experiment demonstrated equivalent shuttle escape deficits resulting from the two types of shock exposure. In addition, behavioral observations made during inescapable shock indicated that those behaviors immediately preceding shock offset during the first several trials were not more likely to develop than other behaviors that were virtually absent early in the session. This pattern of results does not support current competing response hypotheses, but is in agreement with learned helplessness theory.