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.
Highlights
Stimuli with no specific biological relevance for the organism can acquire multiple functions through conditioning procedures
If a light is first established as a discriminative stimulus for key pecking in pigeons, and a tone–light compound is presented in the stage, the tone alone might acquire little or no control of key pecking in later trials
The results showed that even though both stimuli had been repeatedly paired with an unconditioned reinforcer, both the discriminative and reinforcing function of the added stimuli in the compound were blocked
Summary
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. If only one of the elements (A) is paired with the reinforcer prior to the compound-stimulus (A and B) pairings with the reinforcer, stimulus control by B may be weak or absent during a test for stimulus control This phenomenon is referred to as blocking (Williams, 1975). If a light is first established as a discriminative stimulus for key pecking in pigeons, and a tone–light compound is presented in the stage, the tone alone might acquire little or no control of key pecking in later trials.
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