Self-control Choices Research Articles

Developmental Changes in Food Perception and Preference

Food choices are a key determinant of dietary intake, with involved brain regions such as the mesolimbic and prefrontal cortex maturing at a differential rate from childhood to young adulthood. However, developmental changes in healthy and unhealthy food perception and preference remain poorly understood. We aimed to understand this gap by investigating whether perceptions and preferences for food vary as a function of age, and how specific food attributes (i.e., taste and health) impact these age-related changes. We hypothesized that there would be an inverted U-shaped relationship between age and preference for high-calorie foods. As well, we expected that both dietary self-control and the decision weight of the health attribute would increase with age. One hundred thirty-nine participants aged 8–23 years (79 males, 60 females) participated in this study. They completed computerized rating tasks to assess taste, health, and liking (or preference) of high-calorie and low-calorie foods, followed by 100 binary food choices based on each participant’s individual ratings for taste and health. Among the 100 pairs, 75 were deemed challenge trials, where one food had a higher taste rating but a lower health rating than the other food item. Dietary self-control was considered successful when the healthier food cue in the challenge trial was chosen, and self-control success ratio (SCSR) was computed as the proportion of self-control success trials over the total number of choices. Results showed that high-calorie foods were rated as more tasty (r = 0.32, p < 0.001) and less healthy (r = -0.22, p < 0.01) with increasing age. As well, older participants wanted to eat high-calorie foods more than the younger participants (r = 0.29, p = 0.001). Furthermore, older age was associated with an increased decision weight of taste attribute on food preferences (r = 0.26, p = 0.002), suggesting that the taste attribute may contribute to the age-related increases in preference for high-calorie foods. Although participants rated low-calorie foods as less tasty (r = -0.17, p = 0.04) and less healthy (r= -0.31, p < 0.001) with increasing age, there was no significant association between age and preference for low-calorie foods. Participants made faster food choices with increasing age (r= -0.31, p < 0.001), which was driven by failed self-control choices (r = -0.23, p = 0.006). There was no significant association between age and SCSR (p = 0.5). Our results are consistent with other studies that demonstrate age-related increases in consumption of calorie-dense foods in youth, and suggest that age may be more relevant to preference for high-calorie than low-calorie foods. Future studies are merited to investigate the neurobiology underlying these developmental changes in food perceptions and preferences.

Self-Controlled Choice Arises from Dynamic Prefrontal Signals That Enable Future Anticipation.

Self-control allows humans the patience necessary to maximize reward attainment in the future. Yet it remains elusive when and how the preference to self-controlled choice is formed. We measured brain activity while female and male humans performed an intertemporal choice task in which they first received delayed real liquid rewards (forced-choice trial), and then made a choice between the reward options based on the experiences (free-choice trial). We found that, while subjects were awaiting an upcoming reward in the forced-choice trial, the anterior prefrontal cortex (aPFC) tracked a dynamic signal reflecting the pleasure of anticipating the future reward. Importantly, this prefrontal signal was specifically observed in self-controlled individuals, and moreover, interregional negative coupling between the prefrontal region and the ventral striatum (VS) became stronger in those individuals. During consumption of the liquid rewards, reduced ventral striatal activity predicted self-controlled choices in the subsequent free-choice trials. These results suggest that a well-coordinated prefrontal-striatal mechanism during the reward experience shapes preferences regarding the future self-controlled choice.SIGNIFICANCE STATEMENT Anticipating future desirable events is a critical mental function that guides self-controlled behavior in humans. When and how are the self-controlled choices formed in the brain? We monitored brain activity while humans awaited a real liquid reward that became available in tens of seconds. We found that the frontal polar cortex tracked temporally evolving signals reflecting the pleasure of anticipating the future reward, which was enhanced in self-controlled individuals. Our results highlight the contribution of the fronto-polar cortex to the formation of self-controlled preferences, and further suggest that future prospect in the prefrontal cortex (PFC) plays an important role in shaping future choice behavior.

Promoting self-control in overweight and obese children.

Background and objective: impulsiveness might affect the ability of an individual to plan meals, eat regularly, and resist impulses to enjoy foods that are high in fat and sugars in a particular way. The objective of the present study was to evaluate the effectiveness of a fading strategy regarding a reinforcer dimension to promote the development of self-control and decrease impulsive choice among 14 overweight and obese children. Material and methods: to meet this objective, an experimental procedure of choice behavior was used to evaluate the impulsivity and self-control choices influenced by four reinforcer dimensions on a computer: reinforcement rate, reinforcer quality, immediacy of the reinforcement, and response effort. Results: the results indicate that the children's decisions were influenced primarily by the immediacy of the reinforcement and the reinforcement rate; therefore, the children's behavior can be classified as impulsive. Based on these results, a fading procedure was implemented for self-control training in which the immediacy values of the reinforcement and other influential dimensions that devalued the reinforcer were progressively increased. Conclusions: after this fading strategy, a change in preference was observed among the children with regard to the proportion of alternative responses that produced high rates of reinforcement or were of higher quality compared with the allocation of choices associated with immediate reinforcement, which required less effort and were of lower quality. It is possible to design strategies regarding the development of self-control based on the contrasting qualities of these dimensions and the gradual training of tolerance of restrictions on access to the reinforcer.

Spoiling the pleasure of success: Emotional reactions to the experience of self-control conflict in the eating domain.

People often experience self-control conflicts (i.e., feel tempted to indulge while motivated to resist). But, how do people feel after making such conflicted self-control choices? Whereas previous research has focused almost exclusively on the influence of choice outcomes (healthy vs. unhealthy) on emotional reactions (e.g., pride vs. guilt), we propose that the experience of conflict during decision making could have a unique influence, possibly fueling negative emotions (i.e., regret) regardless of people's choice outcomes. To test this, we studied immediate consequences of people's experience of conflict during self-control decision making (healthy vs. unhealthy food choice) on self-conscious emotions (i.e., guilt, regret, or pride), choice satisfaction and future behavior. Across 5 studies (vignette, field, and experience sampling), we found a link between self-control conflict and negativity: the more difficulty (proxy of conflict, Studies 1 and 2) or conflict (Studies 3 and 5) participants experienced during self-control decision making, the more negative they felt about their choice afterward. This was the case for unhealthy as well as healthy choices. Specifically, self-control conflict strength was associated with increased levels of guilt and regret (but not pride), with lower satisfaction and with lowered odds of making a similar choice in the future (Studies 1 to 3). Studies 4 and 5 suggested that conflict strength can boost pride after healthy choices, but only if participants first appraised their choice as acts of self-control. Our findings, therefore, highlight the costs as well as the potential benefits of experiencing conflict during self-control decision making. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Differential reinforcement of low rates differentially decreased timing precision

Timing processes have been implicated as potential mechanisms that underlie self-controlled choice. To investigate the impact of an intervention that has been shown to increase self-controlled choice on timing processes, accuracy and precision of temporal discrimination were assessed in an 18-s peak procedure (18-s fixed interval trials; 54-s peak trials). During an intervention phase, mice in three treatment groups experienced differential reinforcement of low rate (DRL) schedules of reinforcement of 27 s, 18 s, or 9 s. A fourth group received continued exposure to the peak procedure. After the DRL intervention, timing was reassessed using the peak procedure. In contrast to previous reports, the DRL intervention resulted in less precise timing as indicated by increased peak spread and disrupted single-trial measures of temporal control. These effects were only detected just after the DRL intervention suggesting a transient effect of DRL exposure on timing. The increase in peak spread in the present experiment suggests delay exposure via DRL schedules may produce a “dose-dependent” effect on temporal discrimination, which may also increase self-controlled choice.

Neural Correlates of Consumer Buying Motivations: A 7T functional Magnetic Resonance Imaging (fMRI) Study.

Consumer buying motivations can be distinguished into three categories: functional, experiential, or symbolic motivations (Keller, 1993). Although prior neuroimaging studies have examined the neural substrates which enable these motivations, direct comparisons between these three types of consumer motivations have yet to be made. In the current study, we used 7 Tesla (7T) functional magnetic resonance imaging (fMRI) to assess the neural correlates of each motivation by instructing participants to view common consumer goods while emphasizing either functional, experiential, or symbolic values of these products. The results demonstrated mostly consistent activations between symbolic and experiential motivations. Although, these motivations differed in that symbolic motivation was associated with medial frontal gyrus (MFG) activation, whereas experiential motivation was associated with posterior cingulate cortex (PCC) activation. Functional motivation was associated with dorsolateral prefrontal cortex (DLPFC) activation, as compared to other motivations. These findings provide a neural basis for how symbolic and experiential motivations may be similar, yet different in subtle ways. Furthermore, the dissociation of functional motivation within the DLPFC supports the notion that this motivation relies on executive function processes relatively more than hedonic motivation. These findings provide a better understanding of the underlying neural functioning which may contribute to poor self-control choices.

Limited Self-Control and Food Choices Under Varying Workloads: Brain Food Isn't Health Food (in the Field)

Capacities for self-control have consequences for the effectiveness of policies designed to assist individuals in making choices affecting their long run well-being. The strength model from the psychology literature proposes that self-control is a constrained resource whose effectiveness tends to dwindle when an individual attempts to resist multiple sources of temptation at a time. We develop a simple economic framework for the strength model, and test its consequences in the field. Specifically, we analyze the food purchase patterns of university students who face time-varying academic self-control demands. Relative purchase of unhealthy fast foods increases during the week of final exams when students’ workloads are most cognitively demanding, compared to the purchase ratio of such foods during other times of the year. To address the external validity of the field data, and assist in ruling out alternative explanations, we conduct a field survey which includes a snack choice experiment. In the experiment, the main robust and significant predictor of choosing an unhealthy snack over a healthy snack is subjects’ self-reported time needed to complete their academic responsibilities during the upcoming week. As combined evidence, these findings are consistent with an economic model of limited self-control in which individuals must choose how to allocate their self-control between academic activities and eating activities. Consequences and potential policy implications are discussed.

SOBRE POMBOS E GENTE: ALGUMAS OBSERVAÇÕES SOBRE DIFERENÇAS ENTRE ESPÉCIES EM ESCOLHA E AUTOCONTROLE

A continuidade no comportamento entre espécies tem sido amplamente assumida na análise do comportamento, embora pesquisas recentes pareçam desafiar uma versão forte do pressuposto da continuidade. Este artigo apresenta uma revisão de fontes potenciais para a descontinuidade humano-não humano em escolha e auto-controle. Ênfase especial é colocada nas diferenças nos procedimentos empregados para estudar humanos e outros animais, que dificultam comparações entre espécies. Modificações nos procedimentos empregados com não-humanos (por meio do uso de sistemas de reforço do tipo fichas) e com humanos (por meio do emprego de sistemas de reforço do tipo consumatório) mostram maior acordo nos padrões de escolha de humanos e outros animais. Isto sugere que pelo menos algumas das diferenças relatadas sobre escolhas em procedimentos de autocontrole em humanos e outros animais refletem diferenças de procedimento, mais do que diferenças mais fundamentais em processos comportamentais. Ao estreitar as lacunas metodológicas que separam procedimentos empregados com humanos e não humanos, esta pesquisa aponta estratégias mais efetivas para avaliar a continuidade no comportamento entre espécies.Palavras-chave: escolha, autocontrole, reforçamento por fichas, reforço consumatório, continuidade entre espécies.

Acute Stress Impairs Self-Control in Goal-Directed Choice by Altering Multiple Functional Connections within the Brain’s Decision Circuits

Important decisions are often made under stressful circumstances that might compromise self-regulatory behavior. Yet the neural mechanisms by which stress influences self-control choices are unclear. We investigated these mechanisms in human participants who faced self-control dilemmas over food reward while undergoing fMRI following stress. Wefound that stress increased the influence of immediately rewarding taste attributes on choice and reduced self-control. This choice pattern was accompanied by increased functional connectivity between ventromedial prefrontal cortex (vmPFC) and amygdala and striatal regions encoding tastiness. Furthermore, stress was associated with reduced connectivity between the vmPFC and dorsolateral prefrontal cortex regions linked to self-control success. Notably, alterations in connectivity pathways could be dissociated by their differential relationships with cortisol and perceived stress. Our results indicate that stress may compromise self-control decisions by both enhancing the impact of immediately rewarding attributes and reducing the efficacy of regions promoting behaviors that are consistent with long-term goals.

Social setting, intuition and experience in laboratory experiments interact to shape cooperative decision-making.

Recent studies suggest that cooperative decision-making in one-shot interactions is a history-dependent dynamic process: promoting intuition versus deliberation typically has a positive effect on cooperation (dynamism) among people living in a cooperative setting and with no previous experience in economic games on cooperation (history dependence). Here, we report on a laboratory experiment exploring how these findings transfer to a non-cooperative setting. We find two major results: (i) promoting intuition versus deliberation has no effect on cooperative behaviour among inexperienced subjects living in a non-cooperative setting; (ii) experienced subjects cooperate more than inexperienced subjects, but only under time pressure. These results suggest that cooperation is a learning process, rather than an instinctive impulse or a self-controlled choice, and that experience operates primarily via the channel of intuition. Our findings shed further light on the cognitive basis of human cooperative decision-making and provide further support for the recently proposed social heuristics hypothesis.

Social Setting, Intuition, and Experience in Lab Experiments Interact to Shape Cooperative Decision-Making

Recent studies suggest that cooperative decision-making in one-shot interactions is a history-dependent dynamic process: promoting intuition versus deliberation has typically a positive effect on cooperation (dynamism) among people living in a cooperative setting and with no previous experience in economic games on cooperation (history-dependence). Here we report on a lab experiment exploring how these findings transfer to a non-cooperative setting. We find two major results: (i) promoting intuition versus deliberation has no effect on cooperative behavior among inexperienced subjects living in a non-cooperative setting; (ii) experienced subjects cooperate more than inexperienced subjects, but only under time pressure. These results suggest that cooperation is a learning process, rather than an instinctive impulse or a self-controlled choice, and that experience operates primarily via the channel of intuition. In doing so, our findings shed further light on the cognitive basis of human cooperative decision-making and provide further support for the recently proposed Social Heuristics Hypothesis.

Interactions between dorsolateral and ventromedial prefrontal cortex underlie context-dependent stimulus valuation in goal-directed choice.

External circumstances and internal bodily states often change and require organisms to flexibly adapt valuation processes to select the optimal action in a given context. Here, we investigate the neurobiology of context-dependent valuation in 22 human subjects using functional magnetic resonance imaging. Subjects made binary choices between visual stimuli with three attributes (shape, color, and pattern) that were associated with monetary values. Context changes required subjects to deviate from the default shape valuation and to integrate a second attribute to comply with the goal to maximize rewards. Critically, this binary choice task did not involve any conflict between opposing monetary, temporal, or social preferences. We tested the hypothesis that interactions between regions of dorsolateral prefrontal cortex (dlPFC) and ventromedial prefrontal cortex (vmPFC) implicated in self-control choices would also underlie the more general function of context-dependent valuation. Consistent with this idea, we found that the degree to which stimulus attributes were reflected in vmPFC activity varied as a function of context. In addition, activity in dlPFC increased when context changes required a reweighting of stimulus attribute values. Moreover, the strength of the functional connectivity between dlPFC and vmPFC was associated with the degree of context-specific attribute valuation in vmPFC at the time of choice. Our findings suggest that functional interactions between dlPFC and vmPFC are a key aspect of context-dependent valuation and that the role of this network during choices that require self-control to adjudicate between competing outcome preferences is a specific application of this more general neural mechanism.

Preference reversals and effects of D-amphetamine on delay discounting in rats

Impulsive choice is correlated with behavioral problems such as attention-deficit/hyperactivity disorder and substance abuse. Effects of stimulant drug administration on impulsive choice are not consistent and may depend on baseline differences in impulsive choice. A within-session delay-discounting procedure in which choice was between one food pellet delivered immediately (impulsive choice) and three food pellets delivered after increasing delays (self-controlled choice) was used to determine effects of adding and subtracting delays common to both reinforcers on impulsive choice in male Sprague-Dawley rats (n=8). Delay discounting was observed and impulsive choice was quantified using area under the curve (AUC). Adding delays common to both reinforcers decreased impulsive choice and subtracting delays common to both reinforcers increased impulsive choice. Before administration of D-amphetamine (0.03-1.80 mg/kg, intraperitoneally), subjects were rank ordered into a low-AUC or a high-AUC group. Select doses of D-amphetamine decreased impulsive choice for subjects in the low-AUC group but not for subjects in the high-AUC group. These results indicate that impulsive choice can be altered by changing the delay common to both reinforcers and suggest that effects of D-amphetamine may depend, in part, on baseline differences in impulsive choice.

Effects of pre-trial response requirements on self-control choices by rats and pigeons.

Parallel experiments with rats and pigeons examined whether the size of a pre-trial ratio requirement would affect choices in a self-control situation. In different conditions, either 1 response or 40 responses were required before each trial. In the first half of each experiment, an adjusting-ratio schedule was used, in which subjects could choose a fixed-ratio schedule leading to a small reinforcer, or an adjusting-ratio schedule leading to a larger reinforcer. The size of the adjusting ratio requirement was increased and decreased over trials based on the subject's responses, in order to estimate an indifference point-a ratio at which the two alternatives were chosen about equally often. The second half of each experiment used an adjusting-delay procedure-fixed and adjusting delays to the small and large reinforcers were used instead of ratio requirements. In some conditions, particularly with the reinforcer delays, the rats had consistently longer adjusting delays with the larger pre-trial ratios, reflecting a greater tendency to choose the larger, delayed reinforcer when more responding was required to reach the choice point. No consistent effects of the pre-trial ratio were found for the pigeons in any of the conditions. These results may indicate that rats are more sensitive to the long-term reinforcement rates of the two alternatives, or they may result from a shallower temporal discounting rate for rats than for pigeons, a difference that has been observed in previous studies.

Self-Control and Impulsivity in Children: Multiple Behavioral Measures

The present experiment investigated the relationship between laboratory measures of self-control and delay of gratification in children and explored several other factors that may influence self-control. In the self-control paradigm, 30 four-year-old children repeatedly chose between three reinforcers received after a delay and one reinforcer received immediately. A self-imposed delay modification allowed participants to reverse their choices to the smaller, less delayed reinforcer during the delay to the larger reinforcer. In the delay-of-gratification paradigm, the children received three reinforcers if they waited 20 min until the experimenter returned or one reinforcer if they terminated the trial by ringing a bell. A strong positive correlation between the proportion of self-control choices in the self-control paradigm and the wait times in the delay-of-gratification paradigm was found, suggesting concurrent validity between the two measures. In addition, the exposure to visual food cues had no consistent effect across participants on choice in either measure.

EFFECTS OF METHYLPHENIDATE AND MORPHINE ON DELAY‐DISCOUNT FUNCTIONS OBTAINED WITHIN SESSIONS

Four rats responded under a "self-control" procedure designed to obtain delay-discount functions within sessions. Each session consisted of seven blocks, with seven trials within each block. Each block consisted of two initial forced-choice trials followed by five free-choice trials. On choice trials, the rats could press either of two retractable levers. A press on one lever was followed by presentation of a smaller reinforcer (a single dipper presentation of a sucrose solution); a press on the other lever was followed by presentation of a larger reinforcer (four consecutive dipper presentations). The delay associated with the smaller reinforcer always was 0 s, whereas the signaled delay associated with the larger reinforcer increased across blocks (from 0 to 50 s). Under these conditions, the percentage of choices of the larger reinforcer decreased across blocks, and relatively reliable delay-discount functions were obtained within sessions. Doses of methylphenidate (1.0 to 17.0 mg/kg) and morphine (0.3 to 17.0 mg/kg) were then administered prior to selected sessions. Typically, intermediate doses of methylphenidate shifted the discount functions to the right (increased choices of the larger reinforcer). For 2 of the rats, this effect was pronounced; for the other 2 rats, this effect occurred after the range of delays for the larger reinforcer was decreased (0 to 20 s). On the other hand, in most cases morphine produced a slight leftward shift in the discount function (decreased choices of the larger reinforcer). The present procedure appears to be a useful and efficient method to characterize drug effects on an entire delay-discount function. As with many procedures used to study self-control choices, however, sources of control other than reinforcement delay and amount may have been operating in the present study, and these sources must be considered when interpreting drug effects.

Nucleus accumbens core lesions retard instrumental learning and performance with delayed reinforcement in the rat

BackgroundDelays between actions and their outcomes severely hinder reinforcement learning systems, but little is known of the neural mechanism by which animals overcome this problem and bridge such delays. The nucleus accumbens core (AcbC), part of the ventral striatum, is required for normal preference for a large, delayed reward over a small, immediate reward (self-controlled choice) in rats, but the reason for this is unclear. We investigated the role of the AcbC in learning a free-operant instrumental response using delayed reinforcement, performance of a previously-learned response for delayed reinforcement, and assessment of the relative magnitudes of two different rewards.ResultsGroups of rats with excitotoxic or sham lesions of the AcbC acquired an instrumental response with different delays (0, 10, or 20 s) between the lever-press response and reinforcer delivery. A second (inactive) lever was also present, but responding on it was never reinforced. As expected, the delays retarded learning in normal rats. AcbC lesions did not hinder learning in the absence of delays, but AcbC-lesioned rats were impaired in learning when there was a delay, relative to sham-operated controls. All groups eventually acquired the response and discriminated the active lever from the inactive lever to some degree. Rats were subsequently trained to discriminate reinforcers of different magnitudes. AcbC-lesioned rats were more sensitive to differences in reinforcer magnitude than sham-operated controls, suggesting that the deficit in self-controlled choice previously observed in such rats was a consequence of reduced preference for delayed rewards relative to immediate rewards, not of reduced preference for large rewards relative to small rewards. AcbC lesions also impaired the performance of a previously-learned instrumental response in a delay-dependent fashion.ConclusionsThese results demonstrate that the AcbC contributes to instrumental learning and performance by bridging delays between subjects' actions and the ensuing outcomes that reinforce behaviour.

Quantitative analyses of methamphetamine?s effects on self-control choices: implications for elucidating behavioral mechanisms of drug action

The purpose of the present research was to utilize quantitative methods to identify behavioral mechanisms involved in the effects of stimulant drugs on choice in a self-control procedure. A logarithmic equation based upon a combination of the matching law and hyperbolic discounting was used to separate drug-induced changes in sensitivity to reinforcement delay from drug-induced changes in sensitivity to reinforcement amount. Pigeons responded under a concurrent-chains schedule. In the initial link, two keys were illuminated simultaneously and access to the terminal link was controlled by a single random-interval (RI) schedule; pecks on one or the other key lead to its terminal link with a 0.5 probability. In the terminal links, one alternative provided 1-s access to food (the smaller reinforcer) and the other alternative provided 4-s access to food (the larger reinforcer). The signaled delay to the smaller reinforcer always was 2 s, whereas the signaled delay to the larger reinforcer increased from 2 to 40 s within each session, across 10-min blocks. In general, intermediate doses of methamphetamine increased preference for the larger more delayed reinforcer. Quantitative analyses indicated that, in most cases, methamphetamine decreased sensitivity to reinforcement delay. In a few instances, concomitant decreases in sensitivity to reinforcement amount also occurred. These results suggest that a reduced sensitivity to reinforcement delay may be important behavioral mechanism of the effects of stimulants on self-control choices, and that this effect sometimes can be accompanied by a decreased sensitivity to reinforcement amount.

Enhancing Physical Therapy Exercises in Persons with Acquired Brain Injury through a Self-Control Training Procedure

The purpose of the present study was to increase engagement in physical therapy tasks with two adults with acquired traumatic brain injuries while promoting self-control choices. Participants were directed to engage in a designated physical therapy task without programmed reinforcement. Next, participants were presented with two choices: a small amount of a preferred reinforcer delivered immediately and a larger portion of the same reinforcer delivered after a specified level of task engagement. When the participants still exhibited impulsive behavior, a third condition was introduced that involved an additional choice of a large progressively delayed reinforcer. With one of the participants, additional manipulations were required in order to bring about self-control responding. These included modifications of delay values and the implementation of a series of forced choices while the delay associated with the choice was systematically increased. Both participants eventually exhibited a preference for the progressive delay option even as the duration of the delay surpassed that of the fixed delay option. Results are discussed in terms of teaching life enhancing skills and the enhancement of optimal choice making.

Quantitative analyses of methamphetamine's effects on self-control choices: implications for elucidating behavioral mechanisms of drug action.

The purpose of the present research was to utilize quantitative methods to identify behavioral mechanisms involved in the effects of stimulant drugs on choice in a self-control procedure. A logarithmic equation based upon a combination of the matching law and hyperbolic discounting was used to separate drug-induced changes in sensitivity to reinforcement delay from drug-induced changes in sensitivity to reinforcement amount. Pigeons responded under a concurrent-chains schedule. In the initial link, two keys were illuminated simultaneously and access to the terminal link was controlled by a single random-interval (RI) schedule; pecks on one or the other key lead to its terminal link with a 0.5 probability. In the terminal links, one alternative provided 1-s access to food (the smaller reinforcer) and the other alternative provided 4-s access to food (the larger reinforcer). The signaled delay to the smaller reinforcer always was 2s, whereas the signaled delay to the larger reinforcer increased from 2 to 40s within each session, across 10-min blocks. In general, intermediate doses of methamphetamine increased preference for the larger more delayed reinforcer. Quantitative analyses indicated that, in most cases, methamphetamine decreased sensitivity to reinforcement delay. In a few instances, concomitant decreases in sensitivity to reinforcement amount also occurred. These results suggest that a reduced sensitivity to reinforcement delay may be important behavioral mechanism of the effects of stimulants on self-control choices, and that this effect sometimes can be accompanied by a decreased sensitivity to reinforcement amount.