A fragile effect: The influence of episodic memory on delay discounting.

Delay discounting occurs when a reward loses value as a function of delay. Episodic future thinking (EFT) reliably decreases delay discounting. EFT may share cognitive features with recalling episodic memories such as constructive episodic simulation. We therefore explored whether recalling episodic memories also reduces delay discounting. In Experiment 1, participants wrote about episodic memories and recalled those memories before completing a delay discounting task. Episodic memories reduced delay discounting according to one commonly used delay discounting measure (area under the curve) but not another (using the hyperbolic model). Experiment 2 compared the effects of general and episodic memories. Neither general nor episodic memories significantly decreased delay discounting compared with a control "counting" condition, but episodic memories reduced delay discounting compared with general memories under some conditions. In Experiment 3, episodic memories did not decrease delay discounting compared with three other control conditions while EFT did. Experiment 3 therefore found that thinking must be both episodic and future orientated to reduce delay discounting. Together, these results suggest that episodic thinking is not sufficient to reliably decrease delay discounting, rather, features unique to episodic future thinking are required. Episodic memory might reduce delay discounting in some contexts, but this effect is small and fragile.

An experimental approach: Investigating the directive function of autobiographical memory.

Why do we have autobiographical memory and how is it useful? Researchers have proposed a directive function; our experiences guide our behavior, particularly when faced with an open-ended problem. Two experiments (one between-participant and one mixed design) were therefore conducted to test whether success autobiographical memories - any experience when the participant felt successful and competent - are helpful for generating solutions to problem scenarios. One research aim was to experimentally test the directive function as current experimental evidence is limited and results are mixed. Consequently, it is unclear if and how autobiographical memory is helpful for open-ended problem solving. Another aim was to test whether self-efficacy is an important factor that supports open-ended problem solving and thus the directive function. Although success memories enhanced self-ratings of self-efficacy across both experiments, in samples of undergraduate students there was no experimental effect of success autobiographical memories on problem solving. Instead, some participants across the memory and control conditions in both experiments, even when not instructed, recalled autobiographical memories related to the problem scenarios presented in the problem-solving task, and these participants did better at problem solving than those who did not. This may hint to a directive function and is perhaps one reason why there is no experimental effect. Sample and experimental design differences are discussed as potential factors that may contribute to non-significant effects in this study but significant effects in others. Our results highlight the complexity of the directive function, and the difficulty of experimentally testing how autobiographical memory directs behavior.

Reduced access to reinforcement drives delay discounting during experienced delays.

Rewards lose value as a function of delay. Previous studies suggest that delays have a bigger effect on reward value when people must wait during the delay. However, whether delays involve waiting or postponing has often been confounded with whether choices are about hypothetical or real rewards. The current study characterized the effects of waiting and postponing in hypothetical and experiential choice contexts separately. In Experiment 1 we observed steeper delay discounting for waiting than for postponing in choices about both hypothetical money and about experienced computer game points. Two factors potentially contributing to steeper discounting in choices about waiting are reduced access to other rewards and direct costs of waiting. In Experiment 2, we adapted the experiential delay-discounting task to manipulate each factor separately. Reduced access to other reinforcers had a bigger effect on delay discounting than direct costs of waiting. These results underscore the importance of considering the unique influence of waiting and associated opportunity costs in both basic delay-discounting research and in applied contexts.

Preweaning environmental enrichment alters neonatal ultrasonic vocalisations in a rat model for prenatal infections.

OBJECTIVE: Maternal infections are a well-known risk factor for neurodevelopmental defects. Such defects are associated with a range of symptoms, and environmental enrichment (EE) could be a promising approach to rehabilitate these. We used the well-established prenatal poly I:C (polyinosinic-polycytidylic acid) model in rats to examine the effects of preweaning EE on rat pups' ultrasonic vocalisations (USVs) when separated from their mothers. USVs are one of the earliest indicators of a pup's functional level and, thus, well-suited as a marker of neurodevelopmental abnormalities. METHODS: We used a two-by-two factorial design in which pregnant Sprague-Dawley rats received either saline or the viral mimic poly I:C, and one group of pups was exposed to preweaning enrichment. We measured maternal separation-induced USVs both before postnatal day (PND) 7 and after preweaning enrichment on PND 14. RESULTS: Poly I:C significantly reduced the number of USVs on PND 7. EE interacted with the poly I:C treatment in that poly I:C pups in the enrichment group called more, whereas saline pups in the enriched environment called less on PND 14 than the respective controls. CONCLUSION: We showed that the effects of maternal poly I:C on the offspring's USVs could be reduced by early EE. If replicated, it could open novel and safe avenues for treating children of mothers who were exposed to infections during pregnancy.

Choices about whether to wait: Changes in delay discounting without changes in time perception.

Delay discounting occurs when the present, subjective value of a reward decreases as a function of delay. Delay discounting is steeper when individuals must wait during the delay, and delay discounting rates for decisions about waiting are not strongly correlated with those for decisions about postponing without waiting. We examined whether changes in delay discounting in choices about waiting are linked to changes in subjective time perception. In Experiment 1, participants completed an experiential waiting task twice. We established that delay discounting was steeper later in the session. In Experiment 2 participants again completed the delay discounting task twice, and we also tracked time perception across the session using the temporal bisection task. Once again, participants demonstrated steeper discounting during the second discounting task, but time perception did not differ significantly. Additionally, discounting rates were not correlated with subjective time perception. Changes in delay discounting across the session might be understood in terms of context or reference effects.

In Search of the Preference Reversal Zone.

A preference reversal is observed when a preference for a larger-later (LL) reward over a smaller-sooner (SS) reward reverses as both rewards come closer in time. Preference reversals are common in everyday life and in the laboratory and are often claimed to support hyperbolic delay-discounting models which, in their simplest form, can model reversals with only one free parameter. However, it is not clear if the temporal location of preference reversals can be predicted a priori. Studies testing model predictions have not found support for them, but they overlooked the well-documented effect of reinforcer magnitude on discounting rate. Therefore, we directly tested hyperbolic and exponential model predictions in a pre-registered study by assessing individual discount rates for two reinforcer magnitudes. We then made individualized predictions about pairs of choices between which preference reversals should occur. With 107 participants, we found (1) little evidence that hyperbolic and exponential models could predict the temporal location of preference reversals, (2) some evidence that hyperbolic models had better predictive performance than exponential models, and (3) in contrast to many previous studies, that exponential models generally produced superior fits to the observed data than hyperbolic models.

Recently encountered delay lengths produce contrast effects on delay discounting.

People demonstrate shallower delay discounting when they have recently made decisions about smaller amounts of money than when they have recently made decisions about larger amounts of money. That is, recent reward amounts produce a contrast effect on delay discounting. We tested whether a similar contrast effect occurs for delays. We recruited two groups of participants via Mechanical Turk. The shorter-delay group made choices about delays ranging from one day to one month, and the longer-delay group made choices about delays ranging from 14 months to 30 years. Both groups then made choices about the same, intermediate delays (one week to 21 months); the longer delay group showed significantly shallower delay discounting, indicating a contrast effect. This suggests that delay discounting is affected not just by absolute delay length, but by the relative delay length.

Investigating food preference in zoo-housed meerkats.

Understanding food preference among animals in human care can support improvements to welfare through training and day-to-day care (e.g., diet management). Little has been published about food preference in zoo-housed meerkats. Assessing meerkat food preference would be useful, not only for the welfare of that species, but also for developing approaches to assessing food preference in other group-housed, social species. The specific aim of this study was to quantify food preference within the meerkat mob at Wellington Zoo. We developed a simple, cost-effective method for characterizing the food preference hierarchy in meerkats by presenting pairs of foods to the mob as a group. We observed stable preference with the hierarchy for pups closely resembling that for adults. This study demonstrated that it is possible to assess food preference and identify a food preference hierarchy for a group of animals from a social species where it was neither practical nor appropriate to assess individuals' preferences separately.

Assessing potential reinforcement-like effects of brief stimuli unrelated to food reinforcers.

It is widely assumed that reinforcers are biologically relevant stimuli, or stimuli that have been associated with biologically relevant stimuli. However, brief, arbitrary stimuli have also been reported to have reinforcement-like effects, despite being unrelated to biologically relevant stimuli like food. The present study explored the potential reinforcement-like effects of brief stimuli across 5 experiments. In Experiments 1 through 4, pigeon subjects responded for food reinforcement and brief stimulus presentations in a 2-component multiple schedule. Neither baseline response rates nor resistance to change during disruption tests were systematically greater in a component with versus without brief stimulus presentations. Increasing the rate and duration of brief stimulus presentations in Experiment 4 did not reveal reinforcement-like effects when compared directly with food. In Experiment 5, pigeons chose between independent terminal links in a concurrent-chains procedure. Across conditions, varying the location, duration, and rate of brief stimulus presentations in the terminal links had no systematic effects on preference. In contrast, varying rates of food reinforcers resulted in large and reliable shifts in preference. Therefore, the present study found no systematic evidence that brief stimuli unrelated to food reliably increase response rates, resistance to change, or preference. These data demonstrate the value of systematic replication, and a behavioral momentum approach to assessing potential reinforcement-like effects.

The Effects of Machine Balance and Free-Spins Features on Machine Preference and Bet Amounts.

Across two experiments, the current study investigated whether the balance displayed on slot-machine screens affects gamblers' decision making in a manner similar to the "house-money effect" observed in other gambling modes. The balance indicates the total amount the gambler has available to wager from. We manipulated initial slot-machine balance within a simulated slot-machine task. Participants gambled on each of two machines and then were able to switch between the two allowing us to assess the effect of machine balance on both preference and bet amounts. Experiment 1 also manipulated which machine incorporated a free-spins feature. In both experiments participants preferred to wager on, and made larger bets on, machines with higher balances. Experiment 1 replicated previous findings that people prefer to gamble on machines offering free spins. Together, these two experiments identify balance available as an additional slot-machine feature that contributes to slot-machine gambling behavior.

Prevention of the development of problem behavior: A laboratory model.

Few studies have isolated the preventive efficacy of common behavioral strategies like noncontingent reinforcement (NCR) and differential reinforcement of alternative behavior (DRA). The purpose of the current study was to develop and evaluate a laboratory model of these two problem behavior prevention strategies. Undergraduate students participated in a computer simulation, in which clicks to a designated area of the computer screen were analogous to the emergence of problem behavior. The responding of participants in a control group, who experienced a percentile schedule used to mimic the shaping of problem behavior, was compared to that of participants in two experimental groups, each with a history of either DRA or NCR. Between-subjects group comparisons showed that both intervention strategies were equally effective in the prevention of our analog to problem behavior when compared to the control group. The strengths and limitations of a laboratory model for prevention are discussed in light of recent applied work in this area.

Realistic Free-Spins Features Increase Preference for Slot Machines.

Despite increasing research into how the structural characteristics of slot machines influence gambling behaviour there have been no experimental investigations into the effect of free-spins bonus features-a structural characteristic that is commonly central to the design of slot machines. This series of three experiments investigated the free-spins feature using slot machine simulations to determine whether participants allocate more wagers to a machine with free spins, and, which components of free-spins features drive this preference. In each experiment, participants were exposed to two computer-simulated slot machines-one with a free-spins feature or similar bonus feature and one without. Participants then completed a testing phase where they could freely switch between the two machines. In Experiment 1, participants did not prefer the machine with a simple free-spins feature. In Experiment 2 the free-spins feature incorporated additional elements such as sounds, animations, and an increased win frequency; participants preferred to gamble on this machine. The Experiment 3 "bonus feature" machine resembled the free spins machine in Experiment 2 except spins were not free; participants showed a clear preference for this machine also. These findings indicate that (1) free-spins features have a major influence over machine choice and (2) the "freeness" of the free-spins bonus features is not an important driver of preference, contrary to self-report and interview research with gamblers.

Differential effects of 3,4-methylenedioxymethamphetamine, methamphetamine, meta-Chlorophenylpiperazine, and scopolamine on behavioral repetition versus variation in rats.

Acute administration of drugs of abuse, such as MDMA and methamphetamine, disrupts performance on many operant tasks, for example, those used to study memory. This might occur in part because drugs make behavior, in general, more repetitive or more variable, or because they produce a more global disruption to performance. The current study explored this across two experiments by employing Neuringer's 'reinforced variability' procedure. Varied behavior was reinforced at some times during the session and repetitive behavior at other times; lights signalled the behavior required. This procedure allowed an investigation of whether a particular drug made behavior more variable (affected behavior when repetition was required), more repetitive (affected behavior when variability was required), or produced a global disruption (affected both components). In Experiment 1, MDMA increased variability while methamphetamine affected both components. In Experiment 2, m-CPP affected both components while scopolamine affected both components at lower doses and increased variability at higher doses. These results indicate both that the reinforced variability procedure can be used to isolate the specific effects of drugs of abuse on the variability of behavior, and that the specific impact of a given drug needs to be considered when interpreting pharmacological disruptions to operant task performance.

The effect of MDMA on sensitivity to reinforcement rate.

Administration of (±)3,4-methylenedioxymethamphetamine (MDMA) causes memory errors by increasing proactive interference. This might occur because MDMA alters sensitivity to reinforcement. The current 2 experiments investigated this directly by assessing the acute (Experiment 1) and chronic (Experiment 2) effects of MDMA on sensitivity to reinforcement. We presented 5 pairs of concurrent variable interval schedules within each session and calculated sensitivity to reinforcement for 3 acute doses of MDMA. In contrast to the related drug, d-amphetamine, and in spite of producing reductions in response rate, MDMA did not reduce sensitivity to reinforcement rate. Chronic administration of a fixed dose of MDMA following each session reduced response rate but did not affect sensitivity to reinforcement rate. In combination with previous research, these results indicate that related drugs may have different effects on sensitivity to reinforcement and that these effects should be considered when interpreting disruptions to operant task performance caused by drug administration. (PsycINFO Database Record

The effect of reinforcer magnitude on probability and delay discounting of experienced outcomes in a computer game task in humans.

Delay and uncertainty of receipt both reduce the subjective value of reinforcers. Delay has a greater impact on the subjective value of smaller reinforcers than of larger ones while the reverse is true for uncertainty. We investigated the effect of reinforcer magnitude on discounting of delayed and uncertain reinforcers using a novel approach: embedding relevant choices within a computer game. Participants made repeated choices between smaller, certain, immediate outcomes and larger, but delayed or uncertain outcomes while experiencing the result of each choice. Participants' choices were generally well described by the hyperbolic discounting function. Smaller numbers of points were discounted more steeply than larger numbers as a function of delay but not probability. The novel experiential choice task described is a promising approach to investigating both delay and probability discounting in humans.

The disruptive effects of methamphetamine on delayed-matching-to-sample performance reflect proactive interference and are reduced by SCH23390.

Different drugs produce different patterns of impairment on delayed matching-to-sample tasks. For example, (+/-)3,4-methylenedioxymethamphetamine (MDMA) produces an increase in proactive interference. That is, subjects are less accurate when they are required to make a response different to the one they made on the immediately previous trial. The current study assessed whether methamphetamine also produces this particular pattern of disruption in delayed matching-to-sample performance in rats. Methamphetamine primarily reduced accuracy on trials where the correct response differed from the one made on the previous trial. Thus methamphetamine, like MDMA and other stimulant-based drugs of abuse, increased proactive interference. This impairment was reduced by prior administration of the dopamine D1 antagonist SCH23390. These results further extend a general conclusion that a range of stimulant-based drugs may disrupt working memory function indirectly via a tendency to repeat previously made responses and that this disruption is related to D1 receptor activity.

Optimal and nonoptimal choice in a laboratory-based sunk cost task with humans: a cross-species replication.

The current four experiments examined the sunk cost effect-nonoptimal persistence following investment-in a laboratory-based decision-making task with adult humans. Subjects made repeated decisions about whether to persist in a course of action-a fixed-ratio schedule whose response requirements varied unpredictably from one trial to the next-or to abandon it and escape in favor of a new trial with a potentially smaller fixed ratio schedule. Satisfying the ratio requirement produced a brief video clip from a preferred television program. In Experiment 1, sunk-cost errors were less likely in subjects who had previously experienced markedly differential reinforcement for escape. In Experiment 2, stimulus changes correlated with changes in mean response requirement, and these changes reduced sunk-cost errors in a small number of subjects. In Experiment 3, sunk-cost errors occurred more frequently as the ratio of the mean response requirements for persistence and escape approached 1.0. The importance of this variable was further supported by the results of Experiment 4, in which features other than this ratio did not markedly alter performance. These four experiments identified some key determinants of whether humans commit the sunk-cost error and confirmed the utility of video clips as reinforcers in experimental research with humans.

The sunk cost effect with pigeons: some determinants of decisions about persistence.

The sunk cost effect occurs when an individual persists following an initial investment, even when persisting is costly in the long run. The current study used a laboratory model of the sunk cost effect. Two response alternatives were available: Pigeons could persist by responding on a schedule key with mixed ratio requirements, or escape by responding on a second key. In Experiment 1, mean response requirements for persistence and escape were varied across conditions. Pigeons persisted (committing the sunk cost error) when persisting increased the mean response requirement only slightly but not when persisting was sufficiently nonoptimal. Experiment 2 explored more systematically combinations of ratios and probabilities assigned to the schedule key. Persistence varied with the ratio of the mean global response requirements for persistence and escape. In Experiment 3, transitions between ratios were signaled. This reduced nonoptimal persistence, and produced some instances of a reverse sunk cost error--escaping when persistence was optimal. In Experiment 4, it was optimal to escape after the second-smallest ratio ever presented. Pigeons escaped at approximately the optimal juncture, especially in conditions with added signals. Overall, this series of experiments suggests that the sunk cost error may arise in part because persistence is the default behavioral strategy in situations where the contingencies for escape and persistence are insufficiently disparate and/or it is relatively difficult to discriminate when to escape. The study also demonstrates the utility of animal models of complex decision making situations.

Providing a reinforcement history that reduces the sunk cost effect.

The sunk cost error occurs when individuals persist with a non-optimal course of action because they have already invested time or resources in it. The current study examined the effect of specific experiences on the likelihood of the sunk cost error. Six pigeons were given repeated choices between persisting with and escaping from relatively large fixed ratios. In most conditions escaping was the choice pattern producing the smallest mean response requirement. In Experiment 1, four of six pigeons persisted, committing the sunk cost error. Some subjects continued to persist even when persistence increased the mean number of responses to reinforcement by 99. In Experiment 2, the absolute difference between the mean numbers of responses to reinforcement for persistence and escape was increased even further for these subjects, and the relative cost of persistence was increased. Once escape had been established, pigeons were less likely to commit the sunk cost error in some conditions where they had previously made the error frequently. Together, the results of both experiments show changes in the frequency of the sunk cost error caused by specific experiences, and that persistence is likely more sensitive to its relative than absolute costs.

Tolerance to cocaine's effects on schedule-controlled behavior: role of delay between pause-ending responses and reinforcement.

The schedule of reinforcement under which behavior is maintained is an important contributor to whether tolerance to the behavioral effects of cocaine develops. Schedule parameter value (for example, fixed-ratio size) has been shown to affect the development of tolerance under some schedule types but not others, but the specific procedural variables causing this effect remain to be identified. To date, schedule-parameter-related tolerance has developed when a longer pause after reinforcement does not lead to a shorter delay between the response that ends the pause and reinforcement. The current study investigated the importance of this variable in pigeons using a multiple chained Fixed-Ratio 1, Fixed-Time x schedule, in which the first key peck in a trial produced a stimulus change and initiated a delay at the end of which food was presented regardless of whether or not additional pecks were made during the delay. Dose-response curves were assessed before, during and after chronic (daily) administration of cocaine. Tolerance to the pause-increasing effects of cocaine occurred to a similar degree regardless of the scheduled time between the end of the pause and reinforcement. Therefore, the relationship between pause length and delay to reinforcement does not provide an explanation for schedule-parameter-related tolerance.