Three groups of rats were trained and extinguished with continuous (CRF) and partial (PR) reinforcement in the presence of two auditory stimuli differing in amount of similarity along a frequency dimension. Results revealed that in the groups where stimulus similarity was least, a within-subjects reversed partial reinforcement extinction effect (PREE) was found. The results also suggest that as similarity between the stimuli associated with CRF and PR decreased, the magnitude of the reversed PREE increased. This result is in contrast to Rashotte's (1971) predictions concerning the type of PREE produced as stimulus similarity varies along a single dimension. / Master of Science