Reducing impulsive choice: VI. Delay-exposure training reduces aversion to delay-signaling stimuli

A Pavlovian, conditioned-reinforcement approach to reducing impulsive choice

Persistent impulsive choice, preference for a smaller-sooner over a larger-later reward, is associated with consequential life outcomes. Procedures that reduce nonhuman impulsive choice often have long training durations that reduce their translational utility. This experiment sought to alter the behavioral function of the stimulus rats encountered during the delay to the larger-later reward. That putatively aversive delay-signaling stimulus was given an appetitive function through Pavlovian conditioning. Forty Long-Evans rats (20 male) were randomly assigned to undergo Pavlovian training (lever-CS precedes food delivery by 8 s), and the other half underwent unpaired training (CS uncorrelated with food). During the test of impulsive choice that followed, choosing the larger-later reward produced 10-s access to the CS during the 20-s delay to that reward. Pavlovian training significantly increased larger-later reward choice relative to rats in the Unpaired group. The large effect size and ease of training are discussed in the context of potential translational research.

Using sign tracking to experimentally increase self-control in rats

Impulsive choice describes a preference for a smaller-sooner reward (SSR) over a larger-later reward (LLR). A large body of research has examined different procedures for decreasing impulsive choice in nonhuman subjects. One limitation of these procedures is the extensive training duration required to achieve the desired results. To address this limitation, the current experiment examined the effects of a brief course of Pavlovian training, designed to establish a conditioned stimulus (CS) that could be strategically used to encourage LLR choices. Forty male Long-Evans rats were randomly assigned to appetitive Pavlovian or unpaired training. A lever insertion signaled an upcoming unconditioned stimulus (i.e., food presentation) for Pavlovian rats and it acquired CS properties. The lever was uncorrelated with the US in the unpaired group, and it did not acquire CS properties. In the subsequent impulsive-choice assessment, the lever from the training phase served as the lever rats pressed to choose the LLR. After an LLR choice, the lever remained in the chamber during the delay to the LLR, just as the SSR lever remained in the chamber until that reward was delivered. Pavlovian-trained rats sign tracked toward the lever CS and made significantly fewer impulsive choices than did rats in the unpaired group.

Active and passive waiting in impulsive choice: Effects of fixed-interval and fixed-time delays

Behavioral interventions to improve self-control, preference for a larger-later (LL) reward over a smaller-sooner (SS) reward, involve experience with delayed rewards. Whether they involve timing processes remains controversial. In rats, there have been inconsistent results on whether timing processes may be involved in intervention-induced improvements in self-control. Interventions that improved self-control with corresponding timing improvements used fixed-interval (FI) delays, whereas interventions that failed to find corresponding timing improvements used fixed-time (FT) delays. The FI schedule includes a response contingency (active waiting), whereas the FT schedule delivers reward automatically (passive waiting). The present study compared the effects of FI and FT schedules in interventions and impulsive choice tasks to evaluate effects on self-control and timing behavior. The impulsive choice task evaluated preference for an SS option (one pellet after 10-, 15-, 20-, 25-, and 30-s delays) versus an LL option (two pellets after a 30-s delay). The intervention task included forced-choice SS (one pellet after 10 s) and LL (two pellets after 30 s) sessions under FI or FT schedules. FI schedules produced greater sensitivity to SS delay in the impulsive choice task. Both FI and FT interventions increased LL choices. Following choice testing, temporal bisection and peak interval tasks revealed better timing precision for rats with an FI delay experience. Overall, the FI choice contingency was associated with improved temporal attention and timing precision.

Mechanisms of impulsive choice: Experiments to explore and models to map the empirical terrain

Impulsive choice is preference for a smaller-sooner (SS) outcome over a larger-later (LL) outcome when LL choices result in greater reinforcement maximization. Delay discounting is a model of impulsive choice that describes the decaying value of a reinforcer over time, with impulsive choice evident when the empirical choice-delay function is steep. Steep discounting is correlated with multiple diseases and disorders. Thus, understanding the processes underlying impulsive choice is a popular topic for investigation. Experimental research has explored the conditions that moderate impulsive choice, and quantitative models of impulsive choice have been developed that elegantly represent the underlying processes. This review spotlights experimental research in impulsive choice covering human and nonhuman animals across the domains of learning, motivation, and cognition. Contemporary models of delay discounting designed to explain the underlying mechanisms of impulsive choice are discussed. These models focus on potential candidate mechanisms, which include perception, delay and/or reinforcer sensitivity, reinforcement maximization, motivation, and cognitive systems. Although the models collectively explain multiple mechanistic phenomena, there are several cognitive processes, such as attention and working memory, that are overlooked. Future research and model development should focus on bridging the gap between quantitative models and empirical phenomena.

Are the attention checks embedded in delay discounting tasks a valid marker for data quality?

To ensure good quality delay discounting (DD) data in research recruiting via crowdsourcing platforms, including attention checks within DD tasks have become common. These attention checks are typically identical in format to the task questions but have one sensical answer (e.g., "Would you prefer $0 now or $100 in a month?"). However, the validity of these attention checks as a marker for DD or overall survey data quality has not been directly examined. To address this gap, using data from two studies (total N = 700), the validity of these DD attention checks was tested by assessing performance on other non-DD attention checks and data quality measures both specific to DD and overall survey data (e.g., providing nonsystematic DD data, responding inconsistently in questionnaires). We also tested whether failing the attention checks was associated with degree of discounting or other participant characteristics to screen for potential bias. While failing the DD attention checks was associated with a greater likelihood of nonsystematic DD data, their discriminability was inadequate, and failure was sometimes associated with individual differences (suggesting that data exclusion might introduce bias). Failing the DD attention checks was also not associated with failing other attention checks or data quality indicators. Overall, the DD attention checks do not appear to be an adequate indicator of data quality on their own, for either the DD task or surveys overall. Strategies to enhance the validity of DD attention checks and data cleaning procedures are suggested, which should be evaluated in future research. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Pavlovian learning and conditioned reinforcement

Conditioned reinforcers are widely used in applied behavior analysis. Basic research evidence reveals that Pavlovian learning plays an important role in the acquisition and efficacy of new conditioned-reinforcer functions. Thus, a better understanding of Pavlovian principles holds the promise of improving the efficacy of conditioned reinforcement in applied research and practice. This paper surveys how (and if) Pavlovian principles are presented in behavior-analytic textbooks; imprecisions and knowledge gaps within contemporary Pavlovian empirical findings are highlighted. Thereafter, six practical principles of Pavlovian conditioning are presented along with empirical support and knowledge gaps that should be filled by applied and translational behavior-analytic researchers. Innovative applications of these principles are outlined for research in language acquisition, token reinforcement, and self-control.

Testing delay of gratification in rats using a within-session increasing-delay task

In delay discounting, preference reversals refer to shifts in preference from a larger-later reward to a smaller-sooner reward. Steep hyperbolic discounting predicts a preference reversal when a smaller-sooner and larger-later reward both become temporally proximal; prior research is consistent with this prediction. Hyperbolic discounting does not predict a preference reversal, however, after an individual chooses a larger-later reward over a smaller-immediate reward; prior research is inconsistent with this prediction. We sought to replicate and extend these findings using a delay of gratification task in rats. The task included a defection response which allowed rats to reverse their preference after choosing a larger-later sucrose reinforcer to instead obtain a smaller-immediate sucrose reinforcer. In Experiment 1, we found that rats would defect on their choice of the larger-later reinforcer, systematically replicating prior research. We also found that experience on the delay of gratification task led to decreases in defection responses. In Experiment 2, we found that prior experience on an intertemporal choice task, with no opportunity to defect, also led to few defection responses on the delay of gratification task. We discuss our findings in the context of whether inhibitory control or temporal learning could be involved in delay of gratification.

Reducing impulsive choice: VIII. Effects of delay-exposure training in female rats

Impulsive choice may play an important role in serious health-related decisions, like addiction tendencies. Thus, there is merit in exploring interventions that reduce impulsive choice. Delay-exposure training involves extended experience with delayed reinforcement. Following training, delay-exposed rats make fewer impulsive choices than control rats. The reducing effects of delay exposure training on impulsive choice have been replicated in male rats seven times. For the first time, this study evaluated the effects of delay exposure training in female rats. Thirty-six rats were randomly assigned to either delay-exposure or immediacy-exposure training. Then, rats underwent two impulsive choice assessments in which they chose between one immediate pellet or three delayed pellets. In the first assessment, delays increased within-sessions, across trial blocks from 0, 8, 16, to 32 s. In the second assessment, delays to the larger reward increased between-sessions, from 8, 16, 32, to 4 s. Unlike findings with male rats, delay-exposure training produced a reduction in impulsive choice only in the initial five sessions in female rats. Possible reasons for the lack of lasting effect in female rats are discussed and future research directions are identified.

Generalizability of time-based interventions: Effects of choice procedure and smaller-sooner delay

Interventions exposing rats to delayed-reward contingencies attenuate suboptimal impulsive choices, a preference for a smaller-sooner (SS) over a larger-later (LL) reward. Interventions may potentially improve delay-tolerance, timing of delays, and/or discrimination of reward magnitudes. Generalization from the intervention to impulsive choice under different procedures can provide insights into the processes that underlie the intervention effects. Experiment 1 tested intervention effects on systematic-delay (SYS) and adjusting-delay (ADJ) procedures, predicting that intervention effects would be more effective on the SYS procedure with predictable delays. The ADJ procedure did not benefit significantly from intervention, but the SYS procedure, unexpectedly, showed greater impulsive choices following intervention. Experiment 2 tested whether short (5 s) SS intervention delays may have promoted greater impulsivity in the SYS impulsive choice procedure in Experiment 1. Short SS delays in choice and intervention procedures increased impulsive choices in comparison to longer (10 s) delays. Incongruent SS delays in the intervention/choice procedures resulted in negative intervention effects. The results suggest that short SS delays are detrimental to self-control and that specific temporal information generalizes from the intervention to the SYS choice task, but not the ADJ choice task.

Effects of immediate-reinforcement training on delay discounting behavior in rats

Chronic exposure to delayed reinforcement has been shown to increase choice for larger, later reinforcement in a subsequent delay discounting task. In the 3 experiments presented in this paper, the opposite was tested: effects of chronic exposure to immediate reinforcement on choice in a subsequent delay discounting task. In Experiment 1, larger, later reinforcement choice was significantly reduced as a result of exposure to immediate reinforcement, compared to a maturation/handle control group, in experienced, male Lewis rats. In Experiment 2, with naive male and female Wistar rats, and Experiment 3, with naïve male Long Evans rats, the impact of exposure to immediate reinforcement was less robust, but directionally consistent with results from Experiment 1. These results align with some previous work reporting that exposure to immediate reinforcement may decrease choice for larger, later reinforcement in a delay discounting task, and/or blunt maturational increases in choice for larger, later reinforcement. These findings have implications for future research investigating experience-based interventions to manipulate delay discounting behavior. They also have clinical implications for understanding and treating disorders involving maladaptive choice.

Reducing impulsive choice VII: effects of duration of delay-exposure training

Impulsive choice is related to substance use disorders, obesity, and other behaviors that negatively impact human health. Reducing impulsive choice may prove beneficial in ameliorating these maladaptive behaviors. Preclinical research in rats indicates that one reliable method for producing large and lasting reductions in impulsive choice is delay-exposure (DE) training. In all six of the prior DE-training experiments, rats were given extensive experience (~ 120 training sessions) with a delayed reinforcement contingency. The present experiment evaluated if similar large and lasting reductions in impulsive choice could be achieved with less training. The duration of DE training between groups of male Wistar rats was 0 sessions (training ended after a lever-pressing acquisition criterion was met), 30, 60, or 120 sessions. Comparison groups were given the same durations of training with immediate reinforcement. A post-training assessment of impulsive choice was completed using an increasing-delay procedure. For rats assigned to the 60-session condition, impulsive choice was reassessed at a 120-day follow-up. DE training reduced impulsive choice but, contrary to expectation, reductions in impulsive choice did not increase with DE-training duration (no significant training-duration by group interaction). Importantly, 60 sessions of DE training produced reductions in impulsive choice that were comparable to prior published findings and this effect remained significant at the 120-day follow-up. Procedural elements that may be responsible for the DE-training effect, and how they could be improved in future experiments, are discussed.