Blocking of Stimulus Control and Conditioned Reinforcement

Abstract

Stimuli with no specific biological relevance for the organism can acquire multiple functions through conditioning procedures. Conditioning procedures involving compound stimuli sometimes result in blocking, related to the phenomenon of overshadowing. This can affect the establishment of conditioned stimuli in classical conditioning and discriminative stimuli in operant conditioning. The aim of the current experiment was to investigate whether a standard blocking procedure might block the establishment of a conditioned reinforcer—in addition to blocking discriminative control by that stimulus in rats. We used successive discrimination training to establish a tone or a light as a discriminative stimulus for chain pulling, upon which an unconditioned reinforcer (water) was contingent. Next, we trained a tone–light compound stimulus the same way. Finally, we conducted two tests, one for stimulus control and one for a conditioned reinforcing effect on a new response. Little or no discriminative control was evident by the second stimulus, which was added to the previously established discriminative stimulus later during training. The subsequent test showed blocking of conditioned reinforcement in five of the seven rats. Procedures that generate blocking can have a practical impact on attempts to establish discriminative stimuli and/or conditioned reinforcers in applied settings and needs careful attention.