In the typical arrangement, two concurrently available initial-link schedules produce transitions to mutually exclusive terminal-link schedules signaled by different stimuli. Figure 1 shows a schematic of a concurrent-chains procedure. The insights provided by the matching law were extended to characterize the relative strengthening effects of conditioned reinforcers using concurrent-chains procedures. With the introduction of Equation 1 and its extensions (e.g., Herrnstein, 1970), relative response strength as measured by relative allocation of behavior became a major theoretical foundation of the experimental analysis of behavior. Where B 1 and B 2 refer to the rates of responding to the two options and R 1 and R 2 refer to the obtained reinforcement rates from those options. Before returning to a discussion of whether conditioned reinforcers actually strengthen responding, I first examine the contemporary approach to measuring strengthening effects of conditioned reinforcers within the context of matching-law based choice theories and then discuss a more limited body of research examining the strengthening effects of conditioned reinforcers within the context of behavioral momentum theory. But, as will be discussed later, interpreting such changes in rates or patterns of behavior in terms of a strengthening process has been controversial for a long time. In that sense, such stimuli may be considered reinforcers. Somewhat later work showed that stimuli temporally proximate to primary reinforcement could change the rate and pattern of behavior upon which they are contingent in chain schedules of reinforcement (see Gollub, 1977, for review). Thus, the same principles that result in a stimulus acquiring the capacity to function as a conditioned stimulus when predictive of an unconditioned stimulus seem to result in a neutral stimulus acquiring the capacity to function as a reinforcer when predictive of a primary reinforcer.Įvidence for such acquired strengthening effects traditionally came from tests to see if the stimulus could result in the acquisition of a new response or change the rate or pattern of a response under maintenance or extinction conditions (see Kelleher & Gollub, 1962 for review). This acquired capacity to strengthen responding is generally considered to be the outcome of Pavlovian conditioning (e.g., Mackintosh, 1974 Williams, 1994b). “A stimulus that has acquired the capacity to reinforce behavior through its association with a primary reinforcer” ( Bouton, 2007).Īs these definitions suggest, neutral stimuli seem to acquire the capacity to function as reinforcers as a result of their relationship with a primary reinforcer. “A previously neutral stimulus that has acquired the capacity to strengthen responses because it has been repeatedly paired with a primary reinforcer” ( Mazur, 2006). To begin, it may be helpful to consider a couple of definitions of conditioned reinforcement from recent textbooks. Rather, I will briefly review the contemporary approach to studying the strengthening effects of conditioned reinforcers and then consider how recent research has led me to reexamine an old question about the nature of conditioned reinforcement: Do conditioned reinforcers actually strengthen behavior upon which they are contingent? Thus, much of what follows will not be new. Also, when considering a concept like conditioned reinforcement with such a long and storied past, it is difficult to say anything that has not been said before. For more thorough reviews, the interested reader should consider other sources (e.g., Fantino, 1977 Hendry, 1969 Nevin, 1973 Wike, 1966 Williams, 1994a,b). Given the reams of published material and long-running controversies surrounding the concept of conditioned reinforcement, this review will not attempt to be exhaustive. Unfortunately, Bolles' evaluation of conditioned reinforcement appears relevant despite 40 additional years of work on the topic. An influential review of conditioned reinforcement 15 years ago ( Williams, 1994a) opened with a quote from more than 40 years ago lamenting the fact that there may be no other concept in psychology in such a state of theoretical disarray ( Bolles, 1967).
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