Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)




Professor S. Siegel


This thesis surveys the avoidance conditioning literature of the past 30 years and discusses various theories of avoidance learning. The theory that has dominated the field has been the "two-factor avoidance theory". Two-factor theory proposes that avoidance learning is based on the interaction of Pavlovian and instrumental conditioning processes. It is shown how two-factor theory has evolved such that it can adequately handle a majority of experimental findings related to avoidance phenomena. An examination is then made of the role of Pavlovian conditioned inhibition in avoidance conditioning. Recent version of two-factor theory do not adequately account for inhibitory processes in avoidance learning. It is hypothesized that avoidance response-contingent feedback stimuli (FSs) become Pavlovian conditioned inhibitors over the course of avoidance training and that this inhibitory property provide the FS with the capacity to reinforce avoidance behavior. If the inhibitory property accruing to the FS is responsible for its reinforcing capabilities then two converging findings are expected. First, the inhibitory and reinforcing strengths of a FS should covary in a positive manner. A more effective (reinforcing) FS should show greater inhibitory strength at the end of avoidance training than a less effective FS. The results of Experiments 1 and 2 of this thesis confirm this prediction. Second, a pretrained Pavlovian conditioned inhibitor should function as a more powerful reinforcer of avoidance behaviour than non-inhibitory stimuli. Experiments 3 and 4 provide evidence supporting this prediction. The results of Experiment 1-4 taken together support the hypothesis that the conditioned inhibitory properties accruing to a FS are of functional significance for avoidance learning. On the basis of these findings, two-factor theory is revised so that it can account for inhibitory processes. This is done by incorporating Rescorla's contingency model of Pavlovian conditioning into Anger's recent version of two-factor avoidance theory. It is then shown how this revised version of two-factor theory offers a more viable account of avoidance learning than other current theories (e.g., positive reinforcement views, expectancy theories, etc.). It is also shown how revised two-factor theory can handle extinction phenomena once thought to be anomalous to a two-factor approach. Finally, Experiment 5 is designed to test a prediction derived from an extension of the "learned-safety" formulation: that repeated nonreinforced exposure of a FS prior to avoidance training endows the FS with true inhibitory or safety signal properties thus making it an effective reinforcer of avoidance behavior. It is found, contrary to the learned-safety hypothesis, that preexposing the FS retards subsequent avoidance conditioning. This result suggests that simple preexposure in the total absence of aversive events is not a sufficient condition for establishing a safety signal.

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