Behavioral and Associative Effects of Differential Outcomes in Discrimination Learning

Article excerpt

The role of the reinforcer in instrumental discriminations has often been viewed as that of facilitating associative learning between a reinforced response and the discriminative stimulus that occasions it. The differential-outcome paradigm introduced by Trapold (1970), however, has provided compelling evidence that reinforcers are also part of what is learned in discrimination tasks. Specifically, when the availability of different reinforcing outcomes is signaled by different discriminative stimuli, the conditioned anticipation of those outcomes can provide another source of stimulus control over responding. This article reviews how such control develops and how it can be revealed, its impact on behavior, and different possible mechanisms that could mediate the behavioral effects. The main conclusion is that differential-outcome effects are almost entirely explicable in terms of the cue properties of outcome expectancies-namely, that conditioned expectancies acquire discriminative control just like any other discriminative or conditional stimulus in instrumental learning.

This article reviews and critiques the substantial literature on how discrimination learning and performance are affected when response-contingent outcomes differ across reinforced responses. Traditionally, the scheduling of different reinforcers for different responses has been atypical in laboratory studies of discrimination learning, despite that fact that in real-world settings, reinforcers vary considerably from one behavior to another. The contingencies most often studied in the laboratory involve a common reinforcer for all responses, an arrangement that in large part reflects historical ideas about the role of reinforcers in instrumental learning. Besides, discriminative responding often develops quite readily under commonreinforcer conditions, a finding that itself tends to encourage the notion that the important relations in discrimination learning are those between the discriminative stimuli and the responses reinforced in their presence. Without denying the basic processes of how behavior comes under stimulus control, there is more to discrimination learning than just a connection between discriminative stimuli and reinforced responses. This point has been made most forcefully by studies in which discriminative responding yields different reinforcers-that is, differential outcomes.

The differential-outcome paradigm has had a profound impact on our understanding of the behavioral and associative processes involved when subjects learn to respond differentially to different environmental events. It has provided a wealth of useful information about the speed with which discriminations are learned, the ability of learned performances to survive delays between the discriminative stimuli and the opportunity to respond, transfer of performance across disparate stimuli, and the associative relations to which subjects are sensitive and that underlie these behavioral effects. Differential-outcome data have contributed substantially to theoretical analyses of discrimination learning, in particular, and instrumental learning, in general (e.g., Colwill, 1994; Colwill & Rescorla, 1986; Urcuioli & DeMarse, 1996), and to the understanding of diverse issues, such as the nature of working memory (e.g., Honig & Dodd, 1986; Overmier, Savage, & Sweeney, 1999; Urcuioli & Zentall, 1992), the origins of equivalence classes (e.g., Astley & Wasserman, 1999; de Rose, Mcllvane, Dube, Galpin, & Stoddard, 1988; Edwards, Jagielo, Zentall, & Hogan, 1982), the neural bases of associative learning (e.g., Blundell, Hall, & Killcross, 2001; Savage, 2001; Savage & Parsons, 1997; see also Donahoe & Burgos, 2000), and behavioral remediation (e.g., Estévez, Fuentes, Overmier, & González, 2003; Hochhalter & Joseph, 2001; Malanga & Poling, 1992; Overmier et al., 1999).

Given these extensive empirical and theoretical contributions, I cannot discuss each and every one in a way that does them justice. …