Search

The purpose of this review is to introduce the reader to the concepts of delay and probability discounting as well as the major empirical findings to emerge from research with humans on these concepts. First, we review a seminal discounting study by Rachlin, Raineri, and Cross (1991) as well as an influential extension of this study by Madden, Petry, Badger, and Bickel (1997). In doing so, we describe the general procedure used for assessing discounting and the resulting form of the obtained discounting functions. With this as background, we review additional empirical findings that have emerged over the last 20 years, by addressing issues such as time consistency and preference reversals, magnitude effects, and the gain-loss asymmetry. Finally, we conclude with a discussion of more recent developments and their implications for the future of this growing area. (Contains 3 figures and 9 footnotes.)

In a prior study (Stein et al., 2013), we reported that rats pre-exposed to delayed rewards made fewer impulsive choices, but consumed more alcohol (12% wt/vol), than rats pre-exposed to immediate rewards. To understand the mechanisms that produced these findings, we again pre-exposed rats to either delayed (17.5 s; n = 32) or immediate ( n = 30) rewards. In posttests, delay-exposed rats made significantly fewer impulsive choices at 15- and 30-s delays to a larger, later food reward than the immediacy-exposed comparison group. Behavior in an open-field test provided little evidence of differential stress exposure between groups. Further, consumption of either 12% alcohol or isocaloric sucrose in subsequent tests did not differ between groups. Because Stein et al. introduced alcohol concentration gradually (3-12%), we speculate that their group differences in 12% alcohol consumption were not determined by alcohol's pharmacological effects, but by another variable (e.g., taste) that was preserved as an artifact from lower concentrations. We conclude that pre-exposure to delayed rewards generalizes beyond the pre-exposure delay; however, this same experimental variable does not robustly influence alcohol consumption. [ABSTRACT FROM AUTHOR]

Delay discounting describes the devaluation of a reward as the delay to the receipt of the reward increases. Because steep delay discounting is robustly correlated with a number of behavioral problems (e.g., substance dependence, gambling) and some evidence suggests steep discounting precedes and predicts drug-taking in humans and rats, this study sought to experimentally reduce rats' delay discounting. Human stimulant-dependent participants given working-memory training reportedly decreased their rates of discounting relative to a sham-training group (Bickel, Yi, Landes, Hill, & Baxter, 2011). To evaluate the cross-species generality of this effect, 38 male Long-Evans rats, matched on pretraining delay-discounting rates, were randomly assigned to receive 140 sessions of working-memory training or sham training (which required no memory of the sample stimulus). Large between-group differences in working memory were observed after training; however, posttraining delay-discounting rates were undifferentiated across groups. Potential explanations for these findings are discussed. [ABSTRACT FROM AUTHOR]