The training and extinction of learned responses may be associated with the contextual stimuli present. The possible effects of contextual stimuli have been observed in classical and operant conditioning through the processes of extinction and renewal responses. Though extinction involves the weakening of a learned response it does not unlearn the response. The association between the conditioned stimulus (CS) and the unconditioned stimulus (US) may still be present and only seem to be lost due to other forms of imposed learning. Despite the association surviving extinction, there is the question of why the conditioned response (CR) is lost through the extinction process. Several studies have been performed in order to assess the extinction process and its effects on the renewal of learned responses. Pavlov (1927, as cited in Bouton & Bolles, 1979) believed that the loss of the CR was due to inhibition produced in the extinction process. Wagner and Rescorla (1972, as cited in Bouton & Bolles, 1979) proposed an alternate explanation stating that the strength of the CR was dependent on two associations. According to the Rescorla-Wagner Model, the CS-US association is combined with the association of contextual stimuli and the US. This explanation answers the question of how the CS-US association can exist after the extinction process even though the CR was lost. The role of contextual stimuli may be an indicator as to why the CR is lost. An experiment by Bouton and Bolles (1979) explores the influence of contextual stimuli on extinction of conditioned suppression. They broke the subject group of 24 rats into two groups. All of the rats were conditioned in the same manner. The context of the extinction processes differed. The control group was treated in the same context as it was in the conditioning process. The experimental group experienced extinction in a different context. The study was designed to compare the groups based on the strength of the CR after extinction.