Probability and delay discounting of hypothetical sexual outcomes

The present study used the discounting procedure to characterize choice behaviors regarding hypothetical sexual outcomes. Eighty-six adult undergraduate students completed computerized delay and probability discounting tasks concerning hypothetical money and hypothetical sexual activity. Consistent with other discounting findings, hyperbolic and hyperbola-like decay models described individual and group median indifference point data well. These findings contribute to a growing literature on the relevance of the discounting procedure to decision-making processes and suggest that the discounting procedure may be useful for understanding the processes that underlie social problem behaviors associated with impulsive sexual decisions.     

Functional parameters of delay discounting assessment tasks: order of presentation

Several variants in the methods used to estimate delay discounting (DD) have been associated with within-subject differences in degree of DD. This study compared variants in the order of presentation of reward and delay values during assessment of DD of hypothetical cash. Participants were randomly assigned to one of two groups. For one group, the immediate reward values were presented in Ascending order and for the other, they were presented in Descending order. In addition, all participants completed a DD task with the reward values presented in a Random order. Degree of DD, calculated as area under the curve (AUC), was similar between the Ascending and Descending procedures, and was significantly higher with the Random procedure. Within-subjects AUC were positively correlated. Reaction times within choice trials changed systematically as a function of order of presentation of the immediate rewards, and distance to the indifference point within each delay value. Reaction times appear to parallel the effort involved in making the individual choices. Some procedural variants in the assessment of DD yield differences in behavior during the assessment task that affect the magnitude of the estimated delay discounting. Thus, the absolute magnitude of DD may not be directly comparable between methods.     

Parameters of delay discounting assessment: number of trials, effort, and sequential effects.

Procedural variants in estimating delay discounting (DD) have been shown to yield significant within-subject differences in estimated degree of delay discounting as well as variations in the patterns of choice. The purpose of this study was to evaluate the effect of subject control over the number of trials in a delay discounting task, on degree of delay discounting. Participants were assessed with two computerized DD assessments: the full-length method presented participants with a fixed set of 240 trials, and the abbreviated task, where once participants had shown indifference between the immediate and delayed rewards, the remaining trials for that delay value were omitted. While the full-length and abbreviated methods did not differentially affect patterns of choice or estimated delay discounting, the order of presentation (ascending or descending) of immediate rewards produced differences in each measure: rate of delay discounting was significantly lower when estimated with the descending sequence; a larger proportion of area under the discounting curve was concentrated around the indifference point trial with the descending sequence; and a lower correlation was observed between estimates obtained across methods with the descending sequence.     

Appropriate discounting leads to forward-looking ecosystem management

Ecology and economics share many intellectual challenges, such as uncertainty about future system dynamics. An appropriate consideration of our uncertainty about our economic future leads to discounting of benefits of ecosystem services at the lowest possible rate over long time horizons. This more realistic discounting supports much more conservative and sustainable decisions than conventional discounting.     

Discounting the freedom to choose: implications for the paradox of choice

Organisms prefer to make their own choices. However, emerging research from behavioral decision making sciences has demonstrated that there are boundaries to the preference for choice. Specifically, many decision makers find an extensive array of choice options to be aversive, often leading to negative emotional states and poor behavioral outcomes. This study examined the degree to which human participants discounted hypothetical rewards that were (a) delayed, (b) probabilistic, and (c) chosen from a large array of options. The present results suggest that the "paradox of choice" effect may be explained within a discounting model for individual patterns of decision making.     

Delay discounting of saccharin in rhesus monkeys

The value of a reinforcer decreases as the time until its receipt increases, a phenomenon referred to as delay discounting. Although delay discounting of non-drug reinforcers has been studied extensively in a number of species, our knowledge of discounting in non-human primates is limited. In the present study, rhesus monkeys were allowed to choose in discrete trials between 0.05% saccharin delivered in different amounts and with different delays. Indifference points were calculated and discounting functions were established. Discounting functions for saccharin were well described by a hyperbolic function. Moreover, the discounting rates for saccharin in all six monkeys were comparable to those of other non-human animals responding for non-drug reinforcers. Also consistent with other studies of non-human animals, changing the amount of a saccharin reinforcer available after a 10-s delay did not affect its relative subjective value. Discounting functions for saccharin were steeper than we found in a previous study with cocaine, raising the possibility that drugs such as cocaine may be discounted less steeply than non-drug reinforcers.     

Delay of gratification and delay discounting in rats

Delay discounting (DD) and delay of gratification (DG) are two measures of impulsive behavior often viewed as reflecting the same or equivalent processes. However, there are some key differences in the contingencies of reinforcement between the procedures that may have implications for understanding impulsivity. This study used DD and DG procedures to determine if differences in contingencies of reinforcement specified by DD and DG alters how much organisms discount the value of delayed reinforcers. Twenty-four water-deprived rats performed one of two Adjusting Amount procedures, which consisted of repeated choices between a fixed amount of water (250 &mgr;l) delivered after a delay (0, 4, 8, 16, or 32 s) and an adjusting, usually lesser amount delivered immediately. Half of the rats (n=12) performed a DD procedure designed to assess preference for immediate over delayed reinforcers in which they had discrete choices between the immediate and delayed amounts of water. A DG procedure was used for the other half of the rats (n=12). In the DG procedure rats also selected between immediate and delayed alternatives, but if they chose the delayed alternative they could switch to and receive the immediate alternative at any time during the delay to the larger reward. In the DD procedure switching responses were not reinforced but were still recorded and used for analyses. The DD functions of the two groups did not differ significantly. However, at the longer delays, the DG group made significantly fewer switching responses than the DD group. A possible role of response inhibition in the DG procedure is discussed.     

Measurement of delay discounting using trial-by-trial consequences

DELAY DISCOUNTING IN HUMANS WAS INVESTIGATED USING THREE DIFFERENT PROCEDURES: a frequently used discounting procedure with hypothetical rewards and delays; a procedure with hypothetical rewards and delays compressed down to much smaller values; and a contingent procedure in which each choice had a direct consequence. In the contingent procedure, on every trial, participants actually experienced the delay and obtained the reward amount associated with their choice. Each participant was exposed to all three procedures. Orderly temporal discounting patterns were obtained in all three procedures and described well by a hyperbolic model. Comparisons of the data revealed patterns unique to each procedure. The distributions of the discounting measures differed across the three procedures. In the contingent procedure, several subjects showed no discounting, e.g. complete self-control. Procedural factors in studies of impulsivity are discussed, and suggestions are offered for experiments in which the contingent-discounting procedure may prove useful.     

The combined effects of delay and probability in discounting

Human discounting studies have frequently observed hyperbolic discounting of rewards that are delayed or probabilistic. However, no studies have systematically combined delay and probability in a single discounting procedure. Indifference points of hypothetical money rewards that are both delayed and probabilistic were determined. Probabilities were converted into comparable delays according to the h/k constant of proportionality determined by , and discounting rates were calculated. These data provided a very good fit to the hyperbolic model of discounting, suggesting that delay and probability can be combined into a single metric in studies of discounting. The inclusion of a magnitude condition found the Magnitude Effect commonly found in studies of temporal discounting. A temporal resolution of uncertainty condition found no effect. The present paper offers a novel statistical method, within an established framework, for the analysis of data from studies of discounting that combine delay and probability.     

The quick delay questionnaire: a measure of delay aversion and discounting in adults

Individuals with ADHD often display an altered response to delay. To date, assessment of this has typically involved neuropsychological testing-however, such tests are designed specifically for children and may not be suitable for adults. They are also relatively time-consuming and expensive. In the current paper, we describe the initial validation of a short questionnaire to assess delay-related behaviour in adults. The Quick Delay Questionnaire (QDQ) is a 10-item scale. The questionnaire was administered to 575 participants from the normal population (ranging in age from 18 to 77 years). Forty of the original sample were selected at random and tested 1 week later. Data on ADHD, anxiety and depression were also collected. There were two five-item scales-(1) delay aversion; and (2) delay discounting. These had internal consistency and had good reliability. Subscales were differentially associated with ADHD, anxiety and depression. The QDQ is a potentially valuable way of assessing response to delay in adults. Further work is required to validate the scale against direct observation and neuropsychological assessment in clinically ascertained samples.     

Strain differences in delay discounting using inbred rats

A heightened aversion to delayed rewards is associated with substance abuse and numerous other neuropsychiatric disorders. Many of these disorders are heritable, raising the possibility that delay aversion may also have a significant genetic or heritable component. To examine this possibility, we compared delay discounting in six inbred strains of rats (Brown Norway, Copenhagen, Lewis, Fischer, Noble and Wistar Furth) using the adjusting amount procedure, which provides a measure of the subjective value of delayed rewards. The subjective value of rewards decreased as the delay to receipt increased for all strains. However, a main effect of strain and a strain × delay interaction indicated that some strains were more sensitive to the imposition of delays than others. Fitting a hyperbolic discount equation showed significant strain differences in sensitivity to delay ( k ). These data indicate that there are significant strain differences in delay discounting. All strains strongly preferred the 10% sucrose solution (the reinforcer in the delay discounting task) over water and the amount of sucrose consumed was correlated with sensitivity to delay. Locomotor activity was not correlated with delay discounting behavior. Additional research will be required to disentangle genetic influences from maternal effects and to determine how these factors influence the underlying association between heightened delay discounting and neuropsychiatric disorders.     

Response bias is unaffected by delay length in a delay discounting paradigm

This study examined the contribution of response bias to measures of delay discounting in Long-Evans rats (n = 8) using the adjusting amount procedure. Under this procedure, we assessed preference for 150 μl of 10% sucrose solution delivered following a delay over a variable-amount alternative delivered immediately. Bias was calculated based on relative preference when reinforcers were delivered immediately from both alternatives. We extended this assessment procedure to examine preference when rewards from both alternatives were equally delayed (2, 4, 8, or 16 s) in addition to assessing a traditional delay discounting function. Relative preference was similar across delays and slightly larger than 150 μl. These results indicate that response bias was stable and suggests a relative aversion for the adjusting alternative, which may be due to the variability in reward size associated with that alternative.     

Using crowdsourcing to examine relations between delay and probability discounting

Although the extensive lines of research on delay and/or probability discounting have greatly expanded our understanding of human decision-making processes, the relation between these two phenomena remains unclear. For example, some studies have reported robust associations between delay and probability discounting, whereas others have failed to demonstrate a consistent relation between the two. The current study sought to clarify this relation by examining the relation between delay and probability discounting in a large sample of internet users (n = 904) using the Amazon Mechanical Turk (AMT) crowdsourcing service. Because AMT is a novel data collection platform, the findings were validated through the replication of a number of previously established relations (e.g., relations between delay discounting and cigarette smoking status). A small but highly significant positive correlation between delay and probability discounting rates was obtained, and principal component analysis suggested that two (rather than one) components were preferable to account for the variance in both delay and probability discounting. Taken together, these findings suggest that delay and probability discounting may be related, but are not manifestations of a single construct (e.g., impulsivity).     

The neural basis of cultural differences in delay discounting

People generally prefer to receive rewarding outcomes sooner rather than later. Such preferences result from delay discounting, or the process by which outcomes are devalued for the expected delay until their receipt. We investigated cultural differences in delay discounting by contrasting behaviour and brain activity in separate cohorts of Western (American) and Eastern (Korean) subjects. Consistent with previous reports, we find a dramatic difference in discounting behaviour, with Americans displaying much greater present bias and elevated discount rates. Recent neuroimaging findings suggest that differences in discounting may arise from differential involvement of either brain reward areas or regions in the prefrontal and parietal cortices associated with cognitive control. We find that the ventral striatum is more greatly recruited in Americans relative to Koreans when discounting future rewards, but there is no difference in prefrontal or parietal activity. This suggests that a cultural difference in emotional responsivity underlies the observed behavioural effect. We discuss the implications of this research for strategic interrelations between Easterners and Westerners.     

Probabilistic discounting in “certain gain-uncertain loss” and “certain loss-uncertain gain” conditions

Studies on probabilistic discounting typically involve choosing between two outcomes of the same sign (i.e., positive or negative). Commonly, participants are given a choice between a smaller, certain gain and a larger, but uncertain gain, or (less commonly) the options may be a certain, smaller loss and an uncertain, but larger loss. In contrast, participants in this study had to make yes/no decisions as to whether they would accept a financial offer involving a combination of both a gain and a loss. This offer could be either a certain gain which, when accepted, could bring an uncertain larger loss, or a certain loss which, when accepted, could bring an uncertain larger gain. Despite the substantial differences between the alternatives posed in the present study and those in typical discounting studies, the same hyperboloid discounting function that describes the choice between certain and uncertain gains also accurately described choice in the situations presented in the present study. In addition, steeper discounting was observed with a larger uncertain gain than with a smaller uncertain gain. No amount effect was revealed with uncertain losses.     

Within-subject comparison of degree of delay discounting using titrating and fixed sequence procedures

Different procedures are often used across experiments to estimate the degree of delay discounting, a common measure of impulsivity. In all procedures, participants indicate their choice between a reward available immediately and one available after a delay. The present experiment determined whether there are differences in the degree of discounting for a hypothetical $100 produced by a procedure that titrates the immediate amount (titrating sequence procedure) versus a procedure that presents a fixed sequence of immediate amounts (fixed sequence procedure) using a within-subject design. The adult human participants showed no significant differences in degree of discounting between procedures as assessed by a hyperboloid model and the Area Under the Curve. Furthermore, the Area Under the Curve values from the two procedures showed a strong positive correlation. These findings suggest there may be no systematic difference between the degree of delay discounting as estimated by the titrating sequence and fixed sequence procedures. Given the apparent similarities in the results, it appears researchers may be justified in basing their choice of which procedure to use on convenience.     

The genetic basis of delay discounting and its genetic relationship to alcohol dependence

Delay discounting is steeper for individuals who drink heavily or are alcohol dependent, but the reasons for this are unclear. Given the substantial genetic component for alcohol dependence it is not unreasonable to ask whether discounting and alcohol dependence have a genetic relationship. For there to be a genetic relationship, delay discounting must have a genetic component (heritability). A review of the human and animal literature suggests that this is the case. Other literature examining whether discounting is a correlated phenotype in individuals who are genetically predisposed to drink (family history positive individuals and selected lines of rats and mice) is mixed, suggesting that networks of genes are critical for the relationship to be seen. The identities of the genes in this network are not yet known, but research examining polymorphisms associated with differences in discounting is beginning to address this issue.     

The effects of testosterone administration and visual erotic stimuli on nocturnal penile tumescence in normal men

Nocturnal penile tumescence (NPT), as circumference change and rigidity, and REM sleep were measured in eight normal eugonadal men in two controlled experiments. In the first, exposure to erotic film prior to sleep had no effect on frequency of REM or on NPT. In the second placebo controlled experiment 150 mg im testosterone enanthate administration was associated with enhanced rigidity of NPT but with no effect on frequency or circumference change of NPT and no effect on frequency of REM.     

On the scaling interpretation of exponents in hyperboloid models of delay and probability discounting

Previously, we (McKerchar et al., 2009) showed that two-parameter hyperboloid models ( [Green and Myerson, 2004] and [Rachlin, 2006]) provide significantly better fits to delay discounting data than simple, one-parameter hyperbolic and exponential models. Here, we extend this effort by comparing fits of the two-parameter hyperboloid models to data from a larger sample of participants (N = 171) who discounted probabilistic as well as delayed rewards. In particular, we examined the effects of amount on the exponents in the two hyperboloid models of delay and probability discounting in order to evaluate key theoretical predictions of the standard psychophysical scaling interpretation of these exponents. Both the Rachlin model and the Green and Myerson model provided very good fits to delay and probability discounting of both small and large amounts at both the group and individual levels (all R²s > .97 at the group level; all median R²s > .92 at the individual level). For delay discounting, the exponent in both models did not vary as a function of delayed amount, consistent with the psychophysical scaling interpretation. For probability discounting, however, the exponent in both models increased as the probabilistic amount increased—a finding inconsistent with the scaling interpretation.