BLOCKING DESPITE CHANGES IN REINFORCER IDENTITY

Rats were trained on a discriminated operant barpressing task accordin g to a standard blocking design. In some conditions, the reinforcer wa s changed between the pretraining and compound conditioning phases; fo r other conditions, the reinforcer remained the same across phases. In three separate experiments using both between- and within-subject des igns, strong blocking effects occurred regardless of the change in the reinforcer. In a fourth experiment, a multiple schedule of reinforcem ent was used in which response-independent reinforcers were superimpos ed on the schedule of response-contingent reinforcers. The degree of r esponse suppression caused by the free reinforcer was greater when the free reinforcers were the same as the response-contingent reinforcers than when they were different. The role played by the reinforcer iden tity in contingency experiments thus appears to be different from the role it plays in blocking experiments.