Delay discounting of different outcomes: Review and theory

Steep delay discounting is characterized by a preference for small immediate outcomes relative to larger delayed outcomes and is predictive of drug abuse, risky sexual behaviors, and other maladaptive behaviors. Nancy M. Petry was a pioneer in delay discounting research who demonstrated that people discount delayed monetary gains less steeply than they discount substances with abuse liability. Subsequent research found steep discounting for not only drugs, but other nonmonetary outcomes such as food, sex, and health. In this systematic review, we evaluate the hypotheses proposed to explain differences in discounting as a function of the type of outcome and explore the trait- and state-like nature of delay discounting. We found overwhelming evidence for the state-like quality of delay discounting: Consistent with Petry and others' work, nonmonetary outcomes are discounted more steeply than monetary outcomes. We propose two hypotheses that together may account for this effect: Decreasing Future Preference and Decreasing Future Worth. We also found clear evidence that delay discounting has trait-like qualities: People who steeply discount monetary outcomes steeply discount nonmonetary outcomes as well. The implication is that changing delay discounting for one outcome could change discounting for other outcomes.     

The absence of numbers to express the amount may affect delay discounting with humans

Human delay discounting is usually studied with experimental protocols that use symbols to express delay and amount. In order to further understand discounting, we evaluated whether the absence of numbers to represent reward amounts affects discount rate in general, and whether the magnitude effect is generalized to nonsymbolic situations in particular. In Experiment 1, human participants were exposed to a delay‐discounting task in which rewards were presented using dots to represent monetary rewards (nonsymbolic); under this condition the magnitude effect did not occur. Nevertheless, the magnitude effect was observed when equivalent reward amounts were presented using numbers (symbolic). Moreover, in estimation tasks, magnitude increments produced underestimation of large amounts. In Experiment 2, participants were exposed only to the nonsymbolic discounting task and were required to estimate reward amounts in each trial. Consistent with Experiment 1, the absence of numbers representing reward amounts produced similar discount rates of small and large rewards. These results suggest that value of nonsymbolic rewards is a nonlinear function of amount and that value attribution depends on perceived difference between the immediate and the delayed nonsymbolic rewards.     

Determination of discount functions in rats with an adjusting-amount procedure.

An adjusting-amount procedure was used to measure discounting of reinforcer value by delay. Eight rats chose between a varying amount of immediate water and a fixed amount of water given after a delay. The amount of immediate water was systematically adjusted as a function of the rats' previous choices. This procedure was used to determine the indifference point at which each rat chose the immediate amount and the delayed amount with equal frequency. The amount of immediate water at this indifference point was used to estimate the value of the delayed amount of water. In Experiment 1, the effects of daily changes in the delay to the fixed reinforcer (100 microliters of water delivered after 0, 2, 4, 8, or 16 s) were tested. Under these conditions, the rats reached indifference points within the first 30 trials of each 60-trial session. In Experiment 2, the effects of water deprivation level on discounting of value by delay were assessed. Altering water deprivation level affected the speed of responding but did not affect delay discounting. In Experiment 3, the effects of varying the magnitude of the delayed water (100, 150, and 200 microliters) were tested. There was some tendency for the discounting function to be steeper for larger than for smaller reinforcers, although this difference did not reach statistical significance. In all three experiments, the obtained discount functions were well described by a hyperbolic function. These experiments demonstrate that the adjusting-amount procedure provides a useful tool for measuring the discounting of reinforcer value by delay.     

Delay discounting as impaired valuation: Delayed rewards in an animal obesity model

Obesity is a major public health problem, which, like many forms of addiction, is associated with an elevated tendency to choose smaller immediate rather than larger delayed rewards, a response pattern often referred to as excessive delay discounting. Although some accounts of delay discounting conceptualize this process as impulsivity (placing the emphasis on overvaluing the smaller immediate reward), others have conceptualized delay discounting as an executive function (placing the emphasis on delayed rewards failing to retain their value). The present experiments used a popular animal model of obesity that has been shown to discount delayed rewards at elevated rates (i.e., obese Zucker rats) to test two predictions that conceptualize delay discounting as executive function. In the first experiment, acquisition of lever pressing with delayed rewards was compared in obese versus lean Zucker rats. Contrary to predictions based on delay discounting as executive function, obese Zucker rats learned to press the lever more quickly than controls. In the second experiment, progressive ratio breakpoints (a measure of reward efficacy) with delayed rewards were compared in obese versus lean Zucker rats. Contrary to the notion that obese rats fail to value delayed rewards, the obese Zucker rats' breakpoints were (at least) as high as those of the lean Zucker rats.     

Delay discounting of qualitatively different reinforcers in rats

Humans discount larger delayed rewards less steeply than smaller rewards, whereas no such magnitude effect has been observed in rats (and pigeons). It remains possible that rats' discounting is sensitive to differences in the quality of the delayed reinforcer even though it is not sensitive to amount. To evaluate this possibility, Experiment 1 examined discounting of qualitatively different food reinforcers: highly preferred versus nonpreferred food pellets. Similarly, Experiment 2 examined discounting of highly preferred versus nonpreferred liquid reinforcers. In both experiments, an adjusting-amount procedure was used to determine the amount of immediate reinforcer that was judged to be of equal subjective value to the delayed reinforcer. The amount and quality of the delayed reinforcer were varied across conditions. Discounting was well described by a hyperbolic function, but no systematic effects of the quantity or the quality of the delayed reinforcer were observed.     

Delay, Probability, and Social Discounting in A Public Goods Game

A human social discount function measures the value to a person of a reward to another person at a given social distance. Just as delay discounting is a hyperbolic function of delay, and probability discounting is a hyperbolic function of odds-against, social discounting is a hyperbolic function of social distance. Experiment 1 obtained individual social, delay, and probability discount functions for a hypothetical $75 reward; participants also indicated how much of an initial $100 endowment they would contribute to a common investment in a public good. Steepness of discounting correlated, across participants, among all three discount dimensions. However, only social and probability discounting were correlated with the public-good contribution; high public-good contributors were more altruistic and also less risk averse than low contributors. Experiment 2 obtained social discount functions with hypothetical $75 rewards and delay discount functions with hypothetical $1,000 rewards, as well as public-good contributions. The results replicated those of Experiment 1; steepness of the two forms of discounting correlated with each other across participants but only social discounting correlated with the public-good contribution. Most participants in Experiment 2 predicted that the average contribution would be lower than their own contribution.     

DISCOUNTING OF DELAYED REWARDS:

Abstract— In this study, children, young adults, and older adults chose between immediate and delayed hypothetical monetary rewards The amount of the delayed reward was held constant while its delay was varied All three age groups showed delay discounting, that is, the amount of an immediate reward judged to be of equal value to the delayed reward decreased as a function of delay The rate of discounting was highest for children and lowest for older adults, predicting a life-span developmental trend toward increased selfcontrol Discounting of delayed rewards by all three age groups was well described by a single function with agesensitive parameters (all R²s>94) Thus, even though there are quantitative age differences in delay discounting, the existence of an age-invanant form of discount function suggests that the process of choosing between rewards of different amounts and delays is qualitatively similar across the life span     

Smokers discount their drug of abuse in the same way as other consumable rewards

Recent research shows that drug abusers discount delayed monetary rewards more than nonabusers do, and they discount delayed substances of abuse (e.g., drugs) more than delayed money. Furthermore, non-drug-abusers discount food and substances of abuse (e.g., alcohol), more than money. Here, we compare the delay and probability discounting of money with that of a directly consumable reward (chocolate) and with that of a substance of abuse (cigarettes), in a drug-using population (smokers). In line with previous research, we found in two experiments that delay discounting differentiated between smokers and nonsmokers, and between money and a nonabused directly consumable reward (chocolate). In addition, our results show that there appears to be no difference in the extent to which smokers discount their abused substance compared to another directly consumable reward. These findings support the contention that drugs and food are part of the same category of primary reinforcers, whereas money is discounted differently, as a conditioned reinforcer.     

Individual Differences in Delay Discounting: Differences are Quantitative with Gains,but Qualitative with Losses

Research on delay discounting and inter‐temporal choice has yielded significant insights into decision making. Although research has focused on delayed gains, the discounting of losses is potentially important in precisely those areas where the discounting of gains has proved informative (e.g., substance use and abuse). Participants in the current study completed both a questionnaire consisting of choices between immediate and delayed gains and an analogous questionnaire consisting of choices between immediate and delayed losses. For almost all participants, the likelihood of choosing the delayed gain decreased with increases in the wait until it would be received. In contrast, when losses (i.e., payments) were involved, different participants showed quite different patterns of choices. More specifically, although the majority of the participants became increasingly likely to choose to pay later as the delay was increased, some participants appeared to be debt averse, in that they were more likely to choose the immediate payment option when the delay was long than when it was brief. These debt‐averse participants also were more likely to choose to wait for a larger delayed gain than other participants and scored lower on Impulsiveness than those who showed the typical pattern of discounting delayed losses. Taken together, these results suggest that in the case of delayed gains, people differ only quantitatively (i.e., in how steeply they discount), whereas in the case of delayed losses, people differ qualitatively as well as quantitatively, contrary to the common assumption that a single impulsivity trait underlies choices between immediate and delayed outcomes. Copyright © 2016 John Wiley & Sons, Ltd.     

Now for Me,Later for Us? Effects of Group Context on Temporal Discounting

Delayed rewards are less valuable than immediate rewards. This well‐established finding has focused almost entirely on individual outcomes. However, are delayed rewards similarly discounted if they are shared by a group? The current article reports on three experiments exploring the effect of group context on delay discounting. Results indicate that discount rates of individual and group rewards were highly correlated, but that respondents were more willing to wait (decreased discounting) for shared outcomes than for individual outcomes. An explanatory model is proposed suggesting that decreased discount rates in group contexts may be due to the way the effects of both delay and social discounting are combined. That is, in a group context, a person values both a future reward (discounted by delay) and a present reward to another person (discounted by the social distance between them). The results are explained by a combined discount function containing a delay factor and a factor representing the social distance between the decision maker and group members. Practical implications of the fact that shared consequences can increase individual self‐control are also discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Social discounting and delay discounting

Social discounting was measured as the amount of money a participant was willing to forgo to give a fixed amount (usually $75) to another person. In the first experiment, amount forgone was a hyperbolic function of the social distance between the giver and receiver. In the second experiment, degree of social discounting was an increasing function of reward magnitude whereas degree of delay discounting was a decreasing function of reward magnitude. In the third experiment, the shape of the function relating delayed rewards to equally valued immediate rewards for another person was predicted from individual delay and social discount functions. All in all, the studies show that the social discount function, like delay and probability discount functions, is hyperbolic in form. Copyright © 2007 John Wiley & Sons, Ltd.     

Impulsivity in borderline personality disorder: reward-based decision-making and its relationship to emotional distress

Impulsivity in Borderline Personality Disorder (BPD) has been defined as rapid and unplanned action. However, a preference for immediate gratification and discounting of delayed rewards might better account for the impulsive behaviors that appear to regulate emotional distress in BPD. To investigate this, a delay discounting task was administered to 30 outpatients diagnosed with BPD and 28 healthy community controls (all aged 15-24) before and after a mood induction. Trait impulsivity was measured with the Barratt Impulsiveness Scale. The results showed that the BPD group had a greater preference for immediate gratification and higher rate of discounting the delayed reward than the control group. Although the mood induction resulted in increased feelings of rejection and anger in all participants, and the rate of delay discounting changed significantly in the control group, the rate of discounting did not change for the BPD group. There was no evidence of rapid decision-making in the BPD group as response times were similar between the two groups during both trials. Finally, greater general impulsiveness and nonplanning impulsiveness were associated with greater rates of discounting in the BPD group. Together these findings suggest that BPD is characterized by a preference for immediate gratification and tendency to discount longer-term rewards. This characteristic appears to exist independent of feelings of rejection and anger, rather than being reactive to this, and to be related to trait impulsivity.     

Degree of Delay Discounting as a Function of Who Receives the Outcome and the Discounter’s Perceived Level of Social Support

Delay discounting occurs when the subjective value of an outcome decreases as its delivery is delayed. The present study investigated whether how individuals discount delayed outcomes would vary as a function of who would hypothetically experience the outcome and the participants’ perceived level of social support. In Experiment One, 600 university students completed a measure of perceived social support and a discounting task involving four different outcomes, with different groups differing in terms of who would hypothetically receive the outcome being discounted (themselves, their mother, or a classmate). The degree of discounting did not vary as a function of recipient of the outcome, but did vary significantly and inversely with perceived level of social support. Experiment Two replicated the effect of perceived social support in 488 university students, but failed to demonstrate that the degree of discounting varied as a function of the level of social support available to the recipient of the outcome being discounted. These results suggest that people discount outcomes similarly regardless of who will be the recipient of the outcome, but that rates of discounting are reliably altered by the discounter’s own perceived level of social support. The latter finding is potentially informative as to why social-support groups may be valuable in therapeutic environments.     

Time preferences for the very long term

Many important decisions concern outcomes delayed by decades or centuries. Whereas some economists have argued that inter-generational discount rates should be lower than intra-generational rates, three experiments found that inter- and intra-generational discount rates were quite similar. Experiment 1 found that discount rates for long delays (30-900 years) were lower than those for shorter delays (1-30 years) but that, holding delay constant, discount rates for outcomes occurring to future generations were similar to those for outcomes occurring to the present generation. Experiment 2 compared inter-generational discount rates for three different types of outcomes and found similar discount rates for saving lives, improving health, and financial benefits. Experiment 3 found similar inter-generational discounting of life-saving programs that benefit people close to or distant from the decision maker. These studies indicate that the discount rate applied to outcomes occurring to future generations depends on the length of the time delay but not on other factors.     

Heaven can wait. How religion modulates temporal discounting

Evidence suggests that religious systems have specific effects on attentional and action control processes. The present study investigated whether religions also modulate choices that involve higher-order knowledge and the delay of gratification in particular. We tested Dutch Calvinists, Italian Catholics, and Atheists from both countries/cultures using an intertemporal choice task where participants could choose between a small immediate and a larger delayed monetary reward. Based on the Calvinist theory of predestination and the Catholic concept of a cycle of sin–confession–expiation, we predicted a reduced delay tolerance, i.e., higher discount rate, for Italian Catholics than for Dutch Calvinists, and intermediate rates for the two atheist groups. Analyses of discount rates support our hypotheses. We also found a magnitude effect on temporal discounting and faster responses for large than for small rewards across religions and countries/cultures. We conclude that temporal discounting is specifically modulated by religious upbringing rather than by generic cultural differences.     

Magnitude effect contributes to the domain specificity in delay discounting

Discounting is a useful framework for understanding temporal choices. A person who prefers $50 immediately over $100 in 1 month exhibits a higher discount rate than a person deciding to wait for the higher payoff. Although previous research shows that discount rates are domain-specific, we propose an alternative to the domain specificity account. We suggest that differences in discounting alternatives across various domains may result not so much from the domains' nature per se but from differences in perceived attractiveness of the discounted alternatives. We replicated that an illustrative study evidencing domain specificity in discounting (Experiment 1) showed that people's subjective values of the payoffs in domains discounted in this experiment were different (Experiment 2) and used a novel method to match the attractiveness of the available alternatives across domains (Experiment 3). Finally, Experiment 4 showed that when matching was applied, the domain effect disappeared. We conclude that a magnitude effect can, at least partially, explain domain specificity in delay discounting.     

Discounting of food and water in rats shows trait- and state-like characteristics

Delay discounting is the loss in value of an outcome as a function of its delay. The present study focused on examining a trait-like characteristic of delay discounting in a preclinical animal model. Specifically, we were interested in whether there was a positive relation between discounting of 2 different outcomes in rats. That is, would rats that discount delayed food steeply also discount delayed water steeply? In addition, we examined how session-to-session variability in discounting could be attributed to differences between subjects (trait variability) and to differences within subjects (state variability). Finally, we measured discounting from early- to mid-adulthood, allowing us to examine changes in discounting as a function of age. Overall, we found a moderate, positive correlation between discounting of food and discounting of water in rats, providing further evidence that the relative consistency with which individuals discount different outcomes is a trait-like characteristic. In addition, we found a high degree of within-subject variability in discounting, indicating strong state-like differences from session to session. Finally, overall, discounting decreased as a function of age; however, individual-subject data showed variability in how discounting changed across time. Overall, our results show that differences in delay discounting between individuals reflect variability in both trait- and state-like characteristics.     

The enduring effect of availability

The present study addressed whether experienced ease of retrieval of autobiographical events affects trait judgments made immediately and after a delay (Experiment 1) and whether this influence is modulated by either of two discounting instructions (Experiment 2). In Experiment 1, participants first attempted to retrieve 6 or 12 personal memories for different traits and then made ease of retrieval and self-trait judgments immediately or 1 week later. In Experiment 2, participants made immediate ratings and then delayed ratings under 3 instructional manipulations: a generic instruction to repeat these judgments, to make these ratings after they were reminded of their original recall total, or to make these ratings after they had their retrieval ease discounted or augmented. In each experiment, an enduring effect of availability was obtained in that the relationship between ease of retrieval and self-trait rating was only slightly affected by the delay. Being reminded of the original number of recalled memories nullified the relationship between ease of retrieval and trait rating. However, discounting or augmenting ease of retrieval, which altered ease of retrieval ratings, did not. Potential explanations for an enduring effect of availability are discussed.     

Escaping the impulse to immediate gratification: the prospect concept promotes a future-oriented mindset, prompting an inclination towards delayed gratification

People's willingness to postpone receiving an immediate reward in order to gain additional benefits in the future, that is, a tendency to shallow delay discounting, is closely related to one's health, wealth, and happiness. We conducted two experiments investigating how the prospect concept can induce a future-oriented mindset and induce people to behave accordingly. We found that engaging in prospective imagery led the participants to focus on delayed utility over immediate utility in financial decisions (Experiment 1). Participants who received the prospect prime via a scrambled-sentence task decreased their desire to pursue hedonic activities for instant gratification (Experiment 2). Moreover, a state of future orientation mediated the effect of the prospect prime on measures of delayed gratification (Experiments 1 and 2). Thus, reminders of prospect may activate a mindset for future orientation by which delayed gratification is strengthened.     

Gambling and Delay Discounting in Japanese Students

The present study examined the relationship between gambling behavior and delay discounting with Japanese residents. Japanese university students were selected into pathological gambler and non‐gambling control groups using a Japanese version of the South Oaks Gambling Screen. In a discounting task, participants chose individually between a large delayed reward and a smaller immediate reward with varied delays. The discounting rate (k‐value) and the area under the curve were significantly higher and smaller, respectively, for the gambler group than for the control group. These findings show that Japanese gamblers discount delayed rewards more steeply than non‐gambling controls, as has been found in U.S. residents.