Rates Of Delay Discounting Research Articles

The Association Between Delay Discounting and Schizotypal Personality Characteristics in a Nonclinical Sample

Immediacy theory of schizophrenia posits that the behavior of individuals with schizophrenia is controlled to a greater degree by stimuli in the current environment relative to individuals without schizophrenia. Prior research supports this idea by finding that individuals with schizophrenia display steeper rates of delay discounting than those without it. The present study had 272 undergraduate students complete a questionnaire that assessed the presence of schizotypal personality characteristics and then a delay- discounting task that involved five different outcomes. Results demonstrated that schizotypal traits were rarely correlated with rates of discounting and that rates of discounting did not differ between participants scoring low and high on those traits. These results, obtained from a nonclinical sample, thus suggest that the steep rates of discounting observed for individuals with schizophrenia in prior research may have developed after, or as a result of, the schizophrenia or potentially as a result of treatment.

Delay discounting: Concepts and measures.

Delay discounting, one element which underlies decision-making, can be defined as the depreciation of the value of a reward related to the time that it takes to be released. High rates of delay discounting are found in subjects who are willing to forgo greater rewards available only after some length of time and who show a preference for smaller rewards that are available immediately. Widely used as a measure of impulsiveness, delay discounting can be evaluated using experimental tasks. The present review evaluated tasks of delay discounting, their features, measures of evaluation and anomalies, and some variables that can affect delay discounting results and applications in the study of individual and intra-individual differences.

Altruism in time: social temporal discounting differentiates smokers from problem drinkers.

Recent studies on reinforcer valuation in social situations have informed research on mental illness. Social temporal discounting may be a way to examine effects of social context on the devaluation of delayed reinforcers. In prior research with non-drug-using groups, we demonstrated that individuals discount delayed rewards less rapidly (i.e., value the future more) for a group of which they are a member than they do for themselves alone. The current study examined how cigarette smoking and level of alcohol use relate to rates of delay and social temporal discounting. In this study, we used crowd-sourcing technology to contact a large number of individuals (N = 796). Some of these individuals were hazardous-to-harmful drinkers (n = 269), whereas others were non-problem drinkers (n = 523); some were smokers (n = 182), whereas others were nonsmokers (n = 614). Delay discounting questionnaires for individual rewards (me now, me later) and for group rewards (we now, we later; me now, we later) were used to measure individuals' discounting rates across various social contexts. Our analyses found that smokers discounted delayed rewards more rapidly than controls under all conditions. However, hazardous-to-harmful drinkers discounted delayed rewards significantly more rapidly than the non-problem drinkers under the individual condition, but not under the social conditions. This finding suggests that the use of different abused drugs may be associated with excessive discounting in the individual condition and has selective effects when discounting for a group in the social conditions.

Comparison of impulsivity and working memory in cocaine addiction and pathological gambling: Implications for cocaine-induced neurotoxicity

BackgroundThe aim of this study was to compare the cognitive performance of cocaine dependent individuals (CDI) with that of pathological gamblers (PG). Cocaine dependence and pathological gambling share neurobiological vulnerabilities related to addiction, but PG are relatively free of the toxic consequences, such that any additional deficits observed in CDI may be interpreted as pertaining to specific drug effects. MethodsWe used a case–control observational design contrasting multiple measures of impulsivity (UPPS-P trait impulsivity, delay discounting) and executive measures of response inhibition (Stroop) and working memory performance (N-back) between groups of CDI (n=29), PG (n=23), and healthy controls (n=20). We conducted one-way ANOVAs, followed by planned pairwise tests and calculations of Cohen's d to estimate significant differences between the groups. ResultsCDI, as compared to PG, had elevated scores on UPPS-P Negative Urgency and poorer performance on working memory (2-back). PG had steeper delay-discounting rates. Both groups had elevated Positive Urgency and poorer Stroop inhibition compared to controls. Peak amount of cocaine use was negatively correlated with working memory and response inhibition performance. ConclusionWe found cocaine-related specific elevations in Negative Urgency and working memory deficits, putatively identified as cocaine neurotoxicity effects. Other aspects of impulsivity (Positive Urgency, Stroop inhibition) were increased across CDI and PG groups and may reflect vulnerability factors for addiction.

Strain differences in delay discounting between Lewis and Fischer 344 rats at baseline and following acute and chronic administration of d-amphetamine

Stimulant drugs have been shown either to increase or decrease rates of delay discounting (impulsive choice). These mixed findings may result from genetic, neurochemical, or environmental factors. Lewis (LEW) and Fischer 344 (F344) rats have neurochemical and behavioral differences that may be relevant to delay discounting and were used to examine effects of acute and chronic administration of d-amphetamine (d-AMP) on impulsive choice using a within-session delay-discounting procedure. Male LEW (n=8) and F344 (n=8) rats chose between one food pellet delivered immediately and three food pellets delivered after an increasing delay. Saline and d-AMP (0.1, 0.3, 1.0, and 1.7mg/kg) were tested acutely and during chronic d-AMP exposure. Choice for the larger reinforcer decreased as the delay to its presentation increased for both strains at baseline. LEW rats made more impulsive choices than F344 rats as indicated by shorter indifference points, and this is consistent with previous research. Acute administration of d-AMP dose dependently increased larger-reinforcer choice and area under the curve (AUC) for LEW, but not F344 rats. During chronic exposure to d-AMP, larger-reinforcer choice and AUC increased relative to acute administration for F344 rats responding in shorter delay series, but not for F344 rats responding in longer delay series or for LEW rats. Differential effects of acute and chronic administration of d-AMP on impulsive choice in LEW and F344 rats may be a result of various factors, including genetic, neurochemical, and environmental variables. Future research should attempt to tease apart the relative contribution of each of these factors on impulsive choice.

When obese people are more patient than non-obese people. A study of post-surgery individuals in a weight loss association

The main goal of this article is to investigate the rates of delay discounting among obese people treated surgically and belonging to an association of those interested in controlling their weight. We also analyze whether socio-economic status and personality traits explain the existing differences. rates of delay discounting are elicited using real monetary incentives in an economic experiment where subjects are asked to make several choices between a smaller, more immediate reward and larger, more delayed rewards. personality traits are examined using the Five Factor model. interestingly, our results show that obese people display lower discount rates than the reference group. these differences can not be explained by personality traits. We argue that obese people do not have to show larger discount rates. in fact, awareness and commitment, rather than their current bmi, seem to play a more important role in determining this parameter.

Aspects of compulsiveness are inversely related to rates of delay discounting.

Within behavioral psychology, self control can be defined as choosing a larger, but more delayed, reinforcing consequence over a smaller, but more immediately available, reinforcing consequence (see Logue, 1995, for a review). Making the opposite choice, that is choosing the smaller, immediately available consequence over a larger, more delayed reinforcing consequence, would be considered an impulsive response. Although there is nothing inherently good or bad about making either type of response, researchers and practitioners have certainly been interested in promoting the display of self control. Reasons for this promotion include the finding that children who display the ability to make a self-control response experience better life outcomes (e.g., greater academic achievement) than do children who display impulsive responding (e.g., Mischel, Shoda, & Rodriquez, 1989). More specifically, preschool children who could refrain from eating a marshmallow in return for getting multiple marshmallows at a later time demonstrated higher scholastic performance and social skills as adolescents than did preschool children who displayed the impulsive response and ate the immediately available marshmallow. A concept related to impulsive responding is temporal, or delay, discounting. Delay discounting refers to the process by which the subjective value of a reinforcing outcome is diminished because its delivery is delayed. The typical finding is that the longer the delay to the delivery of the outcome, the lower the subjective value the individual places on that outcome at the given moment (see Madden & Bickel, 2010, for discussion on the measurement, analysis, and scope of delay discounting). How steeply the subjective value of the outcome decreases as the delay to the full outcome is increased is referred to as the at which that particular individual discounts that out come. (1) The rate of discounting has also been used as a behavioral measure of impulsivity. Rates of delay discounting have interested researchers because they have been shown to be associated with a number of behavioral disorders such as attention deficit / hyperactivity disorder (see Williams, 2010) and substance abuse (see Yi, Mitchell, & Bickel, 2010). Steep rates of delay discounting have also been associated with pathological gambling (Dixon, Marley, & Jacobs, 2003; see Petry & Madden, 2010). This association may not be surprising, given that pathological gambling can be found listed in the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 2000) under impulse-control disorders that are not otherwise classified. This classification also includes a number of disorders that were at one time considered as compulsive behaviors (e.g., addiction; see Hollander, Berlin, & Stein, 2011, for a discussion). In fact, one can still find references in the literature to terms such as compulsive gambling (e.g., Munoz, Chebat, & Suissa, 2010). Although one can find examples of impulsiveness and compulsiveness being used interchangeably, the exact relationship between compulsive and impulsive behaviors is not clear. Given that a measure of impulsivity (i.e., delay discounting) has been associated with disorders that are considered to involve impulse control (e.g., pathological gambling) and those same disorders are, or at least have been, considered compulsive, then one might predict that impulsivity and compulsiveness would be directly related. In fact, some evidence exists to support the idea that similar neural mechanisms are involved in impulse-control disorders and compulsive behaviors (e.g., Voon et al., 2010). Compulsiveness, however, can involve a preoccupation with certain behaviors or thoughts (Kagan & Squires, 1985). Depending on the preoccupation, one might predict that compulsiveness favors the self-control, rather than the impulsive, response. …

Delay and probability discounting in pathological gamblers with and without a history of substance use problems

Pathological gambling and substance use disorders are highly comorbid, possibly because they both stem from a similar process-impulsivity. Although much data exist regarding the association between delay discounting and these psychiatric disorders, relatively little research has examined probability discounting and its relationship with either substance use or gambling. The goal of the current study was to compare rates of probability and delay discounting in a large population of pathological gamblers with and without a history of substance use problems. Treatment-seeking pathological gamblers with (n = 117) and without (n = 119) a history of substance use problems completed questionnaires about discounting of hypothetical monetary outcomes and the Eysenck Impulsivity Questionnaire. The delay-discounting questionnaire involved choices between a smaller amount of money delivered immediately versus a larger amount delivered later, and the probability questionnaire was comprised of choices between a smaller certain versus a larger probabilistic monetary outcome. Hyperbolic functions estimated delay and probability discounting rates based on the indifference points obtained through the questionnaires. Results revealed significant effects of substance use problem status on delay but not on probability discounting, with no significant correlation noted between the two discounting processes. Only delay discounting correlated with Eysenck impulsivity scores. These data suggest that delay and probability discounting tap different dimensions, and delay discounting is more closely linked with substance use problem histories in pathological gamblers.

Effects of cigarette smoking status on delay discounting in schizophrenia and healthy controls

Background Delay discounting is a measure of future-oriented decision-making and impulsivity. Cigarette smoking is associated with rapid discounting of the value of delayed outcomes. In schizophrenia, however, cigarette smoking improves certain neurocognitive impairments associated with the disorder which may explain the high smoking rates in this population. This study examined the relationship between cigarette smoking and delay discounting in schizophrenia and control participants. Methods A total of N = 130 participants, including those with schizophrenia (n = 68) and healthy controls (n = 62) were assessed on the Kirby Delay Discounting Task and compared across smoking status (smokers; non-smokers) and smoking history (current, former; never smokers). Results Smokers exhibited higher discounting rates (i.e., were more impulsive) than non-smokers of the same diagnostic group. Current and former smokers with schizophrenia exhibited similar and significantly higher discounting rates than never smokers, suggesting that in schizophrenia delay discounting is a trait-dependent phenomenon independent of current cigarette smoking. Consistent with previous studies, there was a trend for higher discounting rates in control current smokers compared to control former and never smokers. Conclusions Smokers with and without schizophrenia have higher rates of delay discounting than non-smokers. However, in schizophrenia, rapid delay discounting appears to be a trait associated with having ever been a smoker (i.e., current and former smoking).

Nucleus accumbens and delay discounting in rats: evidence from a new quantitative protocol for analysing inter-temporal choice

There is evidence that the core of the nucleus accumbens (AcbC) is involved in inter-temporal choice behaviour. A new behavioural protocol was used to examine the effect of destruction of the AcbC on delay discounting in inter-temporal choice schedules in rats. Rats with excitotoxic lesions of the AcbC or sham lesions made repeated choices on an adjusting-delay schedule between a smaller reinforcer (A) that was delivered immediately and a larger reinforcer (B) that was delivered after a delay which increased or decreased depending on the subject's choices. In two phases of the experiment, reinforcer sizes were selected which enabled theoretical parameters expressing delay discounting and sensitivity to reinforcer size to be estimated from the ratio of the indifference delays (i.e. the quasi-stable values of the adjusting delay seen after extended training) obtained in the two phases. In both groups, indifference delays were shorter when the sizes of A and B were 14 and 25 μl than when they were 25 and 100 μl of a 0.6 M sucrose solution. Indifference delays were shorter in AcbC-lesioned than in sham-lesioned rats. Estimates of delay discounting rate based on the ratio of the indifference delays were lower in the AcbC-lesioned than in the sham-lesioned rats. The size sensitivity parameter did not differ between the groups. Adjusting delays in successive blocks of trials were analysed using Fourier transform. The period corresponding to the dominant frequency of the power spectrum and power within the dominant frequency band did not differ between the groups. Destruction of the AcbC increased the rate of delay discounting.

Differences in Delay Discounting of Some Commodities as a Function of Church Attendance

Recent research has suggested that the positive benefits of religiousness that are reported in the literature may be related to “self-control.” The present study attempted to determine whether religiousness, as measured by self reporting of regularly attending church services, would be related to how participants discount delayed outcomes. Three hundred one university students completed a delay-discounting task involving five commodities ($1,000, $100,000, annual retirement income, federal education legislation, and medical treatment). Participants who reported regularly attending church services discounted both monetary amounts significantly more than did participants who reported not regularly attending church services, indicating that church goers placed less value on those commodities than non-church goers. Rates of delay discounting did not differ between groups for the other commodities. These results suggest that religiousness alters how people frame certain decisions involving delayed outcomes, but not others.

Delay discounting, impulsiveness, and addiction severity in opioid-dependent patients

Individuals who abuse drugs show higher delay discounting (DD) rate and impulsiveness scores compared with controls; however, it is unclear if DD rate covaries with severity of the addiction or if an individual's discounting rate can be changed by effective substance abuse treatment. This study compared methadone maintenance treatment (MMT) patients ( n = 30) who had not used illegal drugs for 2 years with drug-using MMT patients ( n = 30) and controls ( n = 25) in terms of addiction severity, DD rate, and impulsiveness. Methadone patients abstinent from illegal drugs scored significantly lower on a number of addiction severity measures than the drug-using methadone patients. In addition, both groups of MMT patients showed significantly higher rates of DD and impulsiveness than the control group; however, no differences in DD rate or impulsiveness were found between the groups of patients. Results suggest that DD rate and impulsiveness may not covary with indicators of addiction severity in MMT patients.

Executive Functioning and Delay Discounting of Four Different Outcomes in University Students

The study investigated a potential relationship between level of executive functioning and rates of delay discounting (i.e., the subjective decrease in the value of an outcome if its delivery is delayed). University students completed an executive-functioning questionnaire and then a delay-discounting task involving four different outcomes (money, cigarettes, dating partner, body image). Results showed that the overall measure of executive functioning was a significant predictor of rates of discounting of three of the four outcomes, and approached significance for the fourth outcome. Further, different subscales of executive functioning were significantly correlated with discounting of different outcomes. These results suggest that executive functioning plays a role in discounting of delayed outcomes and that procedures designed to affect either executive function or delay discounting might result in concomitant changes in the other measure.

TRANSITIONAL AND STEADY-STATE CHOICE BEHAVIOR UNDER AN ADJUSTING-DELAY SCHEDULE

Twelve rats made repeated choices on an adjusting-delay schedule between a smaller reinforcer (A) that was delivered immediately after a response and a larger reinforcer (B) that was delivered after a delay which increased or decreased by 20% depending on the subject's choices in successive blocks of trials. In two phases of the experiment (100 sessions and 40 sessions), reinforcer sizes were selected which enabled theoretical parameters expressing the rate of delay discounting and sensitivity to reinforcer size to be estimated from the ratio of the indifference delays obtained in the two phases. Indifference delays, calculated from adjusting delays in the last 10 sessions of each phase, were shorter when the sizes of A and B were 14 and 25 µl of a 0.6 M sucrose solution than when they were 25 and 100 µl of the same solution. The ratio of the indifference delays was significantly smaller than that predicted on the basis of an assumed linear relation between reinforcer size and instantaneous reinforcer value, consistent with a previous proposal that this relation may be hyperbolic in form. Estimates of the rate of delay discounting based on the ratio of the two indifference delays (mean, 0.08 s(-1)) were similar to values obtained previously using different intertemporal choice protocols. Estimates of the size-sensitivity parameter (mean 113 µl) were similar to estimates recently derived from performance on progressive-ratio schedules. In both phases of the experiment, adjusting delays in successive blocks of trials were analyzed using the Fourier transform. The power spectrum obtained from individual rats had a dominant frequency that corresponded to a period of oscillation of the adjusting delay between 30 and 100 trial blocks (mean, 78). Power in the dominant frequency band was highest in the early sessions of the first phase and declined with extended training. It is suggested that this experimental protocol may have utility in neurobehavioral studies of intertemporal choice.

Hypothetical intertemporal choice and real economic behavior: Delay discounting predicts voucher redemptions during contingency-management procedures.

Delay discounting rates are predictive of drug use status, the likelihood of becoming abstinent, and a variety of health behaviors. Rates of delay discounting may also be related to other relevant behaviors associated with addiction, such as the frequency at which individuals redeem contingency management voucher earnings. This study examined the discounting rates of 152 participants in a buprenorphine treatment program for opioid abuse. Participants received up to 12 weeks of buprenorphine treatment combined with contingency management. Participant's drug use was measured via urine specimens submitted three times a week. Successive negative urine specimens were reinforced with increasing amounts of money. After each negative urine specimen, a participant could either redeem his or her earnings or accumulate it in an account. Analysis of the frequency of redemptions showed that participants with higher rates of delay discounting at study intake redeemed their earnings significantly more often than participants with lower rates of discounting. Age and income also predicted redemption rates. We suggest that delay discounting rates can be used to predict redemption behaviors in a contingency management treatment program and that these findings are consistent with the recent theory of the competing neurobehavioral decision systems.

Effects of acute and repeated nicotine administration on delay discounting in Lewis and Fischer 344 rats

Biological differences may underlie individual differences in impulsive behavior, such as choice for a smaller, more immediate reinforcer over a larger, more delayed reinforcer. Repeated exposure to drugs of abuse may have different effects on such behavior. To evaluate the acute and repeated effects of nicotine on impulsive choice, two strains of rats that have been shown to differ in impulsive choice were tested in a delay-discounting paradigm. Eight Lewis and eight Fischer 344 rats were allowed to choose between one food pellet delivered immediately and three food pellets delivered after a delay. The delay systematically increased in blocks of trials within each session, and the delay value at which the choice for the two alternatives was equal (i.e. the indifference point) was interpolated. Effects of nicotine (0.1-1.0 mg/kg, subcutaneous) on percent choice and indifference points were determined during the acute-testing phase and during the redetermination of effects of each dose after at least 30 sessions of repeated 1.0 mg/kg nicotine exposure. The Lewis rats had shorter indifference points (i.e. made fewer larger-reinforcer choices) compared with the Fischer 344 rats. Acute nicotine administration increased the mean larger-reinforcer choices at the 0.3 mg/kg dose in the Lewis rats and at the 1.0 mg/kg dose in the Fischer 344 rats. After repeated exposure to nicotine, indifference points returned to near-baseline (predrug) levels for both the strains. Strain differences were observed in the rates of delay discounting, and nicotine may decrease the impulsive choice acutely, but this effect does not seem to be long lasting.

Psychological Mechanisms of the Tendency of Super-quick Decay for Delayed Heroin Reinforcement in Heroin Abstainers

Previous researches adopting the Delay Discounting Task(DDT) in behavioral economics suggested that the quick decay for delayed reinforcer is a behavioral process common(Bickel et al.,2007) to a variety of addiction such as alcohol(Petry,2001),nicotine(Mitchell,1999;Bickel,Odum, Madden,1999;Reynolds,Karraker,Horn, Richards,2003;Baker,Johnson, Bickel,2003;Reynolds,Richards,Horn, Karraker,2004;Reynolds,2004),cocaine(Coffey,Gudleski,Saladin, Brady,2003),and opioid or heroin(Madden,Petry,Badger, Bickel,1997;Madden,Bickel, Jacobs,1999;Kirby,Petry, Bickel,1999;Odum,Madden,Badger, Bickel,2000;Giordano et al.,2002;Zhang,Zhou,Li, Shen,2008).It was also discovered that,relative to a general reinforcer(for example money),drug dependence individuals show higher delay discounting rate in dependence drug reinforcer such as drink(Petry,2001),cigarette(Bickel et al.,1999;Field,Santarcangelo,Sumnall,Goudie, Cole,2006;Field,Rush,Cole, Goudie,2007),cocaine(Coffey et al.,2003),and heroin(Madden et al.,1997;1999;Kirby et al.,1999;Odum et al.,2000).However,divergence still exists in researchers' explanations for the nature of super-quick decay for dependence drug in drug dependence individu-als.A relative previous viewpoint(that may be called the hypothesis of avoidance of withdrawal symptoms) claimed that the super-quick decay for dependence drug is a consequence of escaping from or avoidance of withdrawal symptoms in drug dependence individuals(Madden et al.,1997;Bickel et al.,1999).Alternatively,some other researchers claimed that the steep discounting of drug of abuse compared to monetary reinforcers may occur as part of a general process by which primary reinforcers(e.g.drugs or food) are discounted more steeply than conditioned reinforcers(e.g.money),rather than as a unique aspect of addiction(Odum Rainaud,2003).This viewpoint may be called the hypothesis of unconditioned reinforcement effect.However,the reasons underlying the differences in discounting rate between primary and secondary reinforcers are not yet clear,so it is necessary to uncover the mechanisms by which conditioned reinforcers lose value more rapidly with delay than primary reinforcers(Odum Rainaud,2003).The present study explores the psychological mechanisms of tendency of super-quick decay in heroin abstainers during different abstinence phases to delayed heroin rein-forcer by the DDT,in which the measurement of craving in cue-exposure situations taken as the validity index of DDT evaluation.In the present study,124 male heroin abstainers(17～39 years old,M=29.27,SD=5.00) during different abstinence phases(1～29 months,M=12.68,SD=7.58) were selected to administer Chinese computerized version of the DDT which was based on monetary rewards and heroin rewards,respectively.In the DDT based on mone-tary rewards,subjects had to choose between hypothetical monetary rewards available immediately or following a delay.Delayed rewards were $10,000 in value;and in the DDT based on heroin rewards,subjects had to choose between hypothetical heroin rewards available immediately or following a delay.Delayed rewards were 250 bags,which was equal to $10,000 in value.The immediate-reward amount would be adjusted until choices reflected indifference in the DDT based on monetary rewards or heroin rewards,and these processes were re-peated at each of eight delays(6 hours to 25 years).Moreover,28 of 124 heroin abstainers were selected to elicit heroin desiring by the cueexposure paradigm.The results of the present study showed that(1) Hyperbolic discounting functions provided a good fit for the subjects discounting data of both delayed reinforcement conditions,and median R2 was from 0.91 to 0.90 for monetary and heroin rewards.(2) Relative to monetary rewards,the delay discounting rates(k) of heroin ab-stainers were much higher for heroin rewards along with the abstinence time course,Z = 7.688,p0.001.(3) The k based on the DDT in heroin abstainers did not improve along with the abstinence time course,χ2money=0.603,df=2,p0.10,χ2heroin=0.806,df=2,p0.10.(4) The delay discounting rates(k) for heroin rewards were correlated with the heroin craving on the cue-exposure paradigm,r=0.47,df=26,p0.01,and heroin craving of super-quick decay group was much higher than that of low-quick decay group,t=2.343,df=26,p0.05.(5) The delay dis-counting rates(k) for heroin rewards were correlated with the k for monetary rewards,r=0.52,df=122,p0.001,and k of higher impulsive group was much higher than that of low impulsive group,U=209.500,p0.001.From the present study we concluded that(1) Heroin abstainers are characterized in tendency of super-quick decay for delayed reinforcement to heroin in the delay discounting task,and the characteristics in heroin abstainers do not improve along with the abstinence time course.(2) The tendency may be an interactional outcome of heroin abstainers' trait impulsivity and heroin cue eliciting,and their accelerated amount relative to monetary rewards in DDT may be manifested as the heroin cue-eliciting effect.

Delay discounting as a mediator of the relationship between perceived stress and cigarette smoking status in adolescents

There has been a wealth of research providing evidence for the relationship between stress and cigarette smoking during adolescence. Despite this knowledge, little is known about possible behavioral mechanisms by which stress exerts its influence on the decision to smoke. This study sought to examine one such behavioral characteristic, delay discounting, that may mediate the relationship between stress and cigarette smoking. Delay discounting generally refers to the discounting of value for outcomes because they are delayed; and high rates of delay discounting have been linked to impulsive behavior. For the current research, adolescent smokers (n = 50) and nonsmokers (n = 50) were compared using a self-report measure of perceived stress and a laboratory assessment of delay discounting. Smokers tended to report higher levels of stress and to discount more by delay, and there was a significant association between reported stress and delay discounting. In addition, delay discounting mediated the relationship between stress and cigarette smoking status. These results suggest that discounting by delay may be a behavior through which stress exerts influence on an adolescent's decision to smoke.

Effects of variable training, signaled and unsignaled delays, and d-amphetamine on delay-discounting functions

One common procedure for obtaining delay-discounting functions consists of a choice between a larger reinforcer that is presented after an increasing delay and a smaller reinforcer that is always presented immediately within session. Repeating the same context of delay presentation (e.g. ascending delay order) in a discrete-choice paradigm, however, may lead to a perseverative response pattern when rats are used as subjects. The purpose of this study was to increase the variability in delay presentation (i.e. ascending and descending delays) in an attempt to reduce a perseverative response pattern and gain tighter control over choice by reinforcer amount and delay. For one group of rats (n = 8), delays to reinforcer presentation were differentially signaled by a flashing houselight and for one group of rats (n = 8) the delays were unsignaled. Effects of delay signal and d-amphetamine on choice were evaluated in both groups. Similar rates of delay discounting and area under the curve (AUC) were observed with both ascending and descending delay presentations and with signaled and unsignaled delays to reinforcement. Increasing the variability in delay order resulted in differences in the choice pattern during 0-s probe sessions. d-Amphetamine had little or no effect on AUC at low doses, but decreased AUC at the highest doses tested, that is, 1.0 and 1.7 mg/kg. Some of the changes in AUC after d-amphetamine administration may have been because of disruption in discrimination of the different food amounts.

Reward contrast in delay and probability discounting

In this study, we examined whether reward contrast influences choice between delayed and probabilistic outcomes. Specifically, we predicted that the subjective value of an intermediate reward would seem relatively larger or smaller, respectively, if it followed choices involving a smaller or larger reward and would produce corresponding changes in rates of delay and probability discounting. In Experiment 1, subjects made choices about hypothetical $5,000 or $50 outcomes and then made choices about $500 outcomes. Delay-discounting rates for the $500 outcome were larger for Group $5,000 than for Group $50, whereas the opposite result was obtained for probability-discounting rates. In Experiment 2, we used a design that allowed for contrast effects to be assessed within subjects. Two groups made choices about delayed or probabilistic rewards. After completing question blocks in which the amount was $5,000 or $50, subjects responded to questions with an intermediate amount ($475/$525). For Group Delay, the present value of the intermediate reward was greater after the $50 block than after the $5,000 block, whereas the opposite was obtained for Group Probability. The results from both experiments confirmed the predictions of reward contrast and suggested that the subjective value of a monetary reward varies inversely with the prior reward amount.