This review critically analyzes experimental data relevant to the concept of conditioned reinforcement. The review has five sections. Section I is a discussion of the relationship between primary and conditioned reinforcement in terms of chains of stimuli and responses. Section II is a detailed analysis of the conditions in which the component stimuli in chained schedules of reinforcement will become conditioned reinforcers; this section also analyzes studies of token reinforcement, observing responses, switching responses, implicit chained schedules, and higher-order conditioning. Section III analyzes experiments in which potential conditioned reinforcers are used either to prolong responding or to generate responding during experimental extinction. This section discusses hypotheses that have been offered as alternatives to the concept of conditioned reinforcement and hypotheses concerning the necessary and sufficient conditions for establishing a conditioned reinforcer. Section IV discusses other variables that act when a conditioned reinforcer is being established or that act when an established conditioned reinforcer is used to develop or maintain behavior. Section V is a general discussion of conditioned reinforcement. The evidence indicates that the conditioned reinforcing effectiveness of a stimulus is directly related to the frequency of primary reinforcement occurring in its presence, but is independent of the response rate or response pattern occurring in its presence. Results from chained schedules comprised of several components indicate that a stimulus can be established as a conditioned reinforcer by pairing it with an already established conditioned reinforcer rather than a primary reinforcer; however, this type of higher-order conditioning has not been clearly demonstrated with respondent conditioning procedures. Although discriminative stimuli are usually conditioned reinforcers, the available evidence indicates that establishing a stimulus as a discriminative stimulus is not necessary or sufficient for establishing it as a conditioned reinforcer. Discriminative stimuli in chained schedules with several components are not always conditioned reinforcers; stimuli that are simply paired with reinforcers can become conditioned reinforcers. The hypotheses that have been offered as alternatives to the concept of conditioned reinforcement are too limited to integrate the data that exist. The concepts of conditioned reinforcement and chained schedule, however, can be used to integrate the data obtained with diverse techniques. Recent experiments have revealed several techniques for the development of effective conditioned reinforcers. These techniques provide a powerful tool for advancing understanding of conditioned reinforcement and for extending control over behavior.
