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.

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.

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.

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.

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.

Whatever gave you that idea? False memories following equivalence training: a behavioral account of the misinformation effect.

The misinformation effect is a term used in the cognitive psychological literature to describe both experimental and real-world instances in which misleading information is incorporated into an account of an historical event. In many real-world situations, it is not possible to identify a distinct source of misinformation, and it appears that the witness may have inferred a false memory by integrating information from a variety of sources. In a stimulus equivalence task, a small number of trained relations between some members of a class of arbitrary stimuli result in a large number of untrained, or emergent relations, between all members of the class. Misleading information was introduced into a simple memory task between a learning phase and a recognition test by means of a match-to-sample stimulus equivalence task that included both stimuli from the original learning task and novel stimuli. At the recognition test, participants given equivalence training were more likely to misidentify patterns than those who were not given such training. The misinformation effect was distinct from the effects of prior stimulus exposure, or partial stimulus control. In summary, stimulus equivalence processes may underlie some real-world manifestations of the misinformation effect.

An animal model of slot machine gambling: the effect of structural characteristics on response latency and persistence.

Despite the prevalence of problem gamblers and the ethical issues involved in studying gambling behavior with humans, few animal models of gambling have been developed. When designing an animal model it is necessary to determine if behavior in the paradigm is similar to human gambling. In human studies, response latencies following winning trials and near win trials are greater than those following clear losses. Weatherly and Derenne (Anal Gambl Behav 1:79-89, 2007) investigated whether this pattern was found with rats working in an animal analogue of slot machine gambling. They found a similar pattern of response latencies but the subjects' behavior did not come under control of the visual stimuli signalling the different outcomes. The animal model of slot machine gambling we used addressed procedural issues in Weatherly and Derenne's model and examined whether reinforcer magnitude and the presence of near win trials influenced response latency and resistance to extinction. Response latencies of the six female Norway Hooded rats varied as a function of reinforcer magnitude and the presence of near-win trials. These results are consistent with prior research and with the idea that near win trials serve as conditional reinforcers.

Human performance on a two-alternative rapid-acquisition choice task.

Davison and Baum [Davison, M., Baum, W. M., 2000. Choice in a variable environment: every reinforcer counts. Journal of the Experimental Analysis of Behavior 74, 1-24.] developed a concurrent-schedule procedure where, within each session, different reinforcer ratios were arranged across components separated by brief black-outs. Behaviour adapted quickly to the reinforcer ratios and reinforcers also had local effects on responding. This procedure has been used with pigeons and rats. In the present experiment, we adapted the Davison and Baum procedure to study the effects of reinforcement on human choice behaviour. Eighteen participants were presented with four different reinforcer ratios within a single 50-minute session. Mean sensitivity to the reinforcer ratios increased within components, and preference was greater for the just-reinforced response alternative immediately following reinforcer delivery, similar to the results from non-human experiments. Although there were limitations to the current procedure, the local time scale analyses are a novel way of examining human operant behaviour.

Discrimination of flicker frequency rates in the reptile tuatara (Sphenodon ).

By investigating the mechanisms that underlie the perception of environmental cues, we may begin to understand how the sensory system governs behavioral responses. This is the first empirical study to examine learning and visual sensitivity in a reptile species, the tuatara (Sphenodon punctatus). We established a non-intrusive psychophysical method by employing an instrumental paradigm in order to examine discrimination learning and the ability to distinguish different flicker frequencies in the tuatara. Seventeen tuatara were trained under an operant conditioning task to respond to various discriminative stimuli flickering between 2.65 and 65.09 Hz. Tuatara were able to learn the operant task and discriminate between a constant light and flicker frequency rates between 2.65 and 45.61 Hz, but not at 65.09 Hz. We demonstrated a reliable psychophysical method where these reptiles could learn a basic operant task and discriminate visual stimuli in the form of flicker frequency rates. The tuatara's ability to perceive flickering light is comparable to that of avian, mammalian, and other reptilian species. This method is thus suitable for more comprehensive examinations of vision and additional sensory abilities in other reptiles.

Attenuation of the disruptive effects of (+/-)3,4-methylene dioxymethamphetamine (MDMA) on delayed matching-to-sample performance in the rat.

Recent evidence suggests that the disruptive effects of acute exposure to (+/-)3,4-methylene dioxymethamphetamine (MDMA) on memory performance may be the result of increased confusion between previous-trial and current-trial events. The current study tested this hypothesis by examining the effects of MDMA on performance of rats in a delayed matching-to-sample procedure when the length of the intertrial interval (ITI) was altered. Consistent with the possibility that limiting the conditions under which responses made on a previous trial would interfere with current-trial choice, a 15-s ITI ameliorated the disruptive effects caused by MDMA on trial performance when the ITI was 5 s. Therefore, the disruptive effects of MDMA on memory can be attenuated by methods that separate current-trial "to-be-remembered" events from previous-trial events.

Using source cues and familiarity cues to resist imagination inflation.

To investigate whether people can resist imagination inflation--the imagination-induced increased confidence that fictitious childhood events really happened--we gave them different types of cues. In a three-stage procedure, participants: (1) rated their confidence that a list of childhood events had happened to them, (2) imagined some of these events, and (3) made confidence ratings a second time. Subjects received either no cues about the source of the imagined event, an additional source cue (perspective), an additional familiarity cue (a plausibility questionnaire), or both cues. Only subjects who had both types of cues resisted imagination inflation. These results suggest that additional cues can sometimes safeguard people from becoming more confident that fictitious events were genuine experiences.

(+/-)3,4-methylenedioxymethamphetamine, d-amphetamine, and cocaine impair delayed matching-to-sample performance by an increase in susceptibility to proactive interference.

This study compared the effects of (+/-)3,4-methylenedioxymethamphetamine, d-amphetamine, and cocaine on performance of rats in a delayed matching-to-sample procedure using a variety of indices of performance to determine the mechanism by which working memory task impairments arise. All 3 drugs produced an overall delay-independent decrease in accuracy rather than a delay-dependent increase in the rate of forgetting. This impairment arose as a result of current-trial choice responses being progressively more affected by responses made in the immediately preceding trial as drug dose increased. Therefore, all 3 drugs produced qualitatively similar disruptions in memory task performance best characterized as an impairment arising from proactive sources of interference.

Choice with initial and terminal link reinforcement: an alternative self-control paradigm.

Self-control is demonstrated when a less desirable immediate outcome is chosen to ensure a substantially better future. In a novel animal analogue of this situation, primary reinforcement was delivered in both the initial and terminal links of a concurrent chain schedule. Rats made initial link choices between equal amounts of ethanol-free or ethanol-containing milk. Choosing the ethanol-free reinforcer resulted in delivery of the larger terminal link reinforcer and was thus analogous to self-control. Self-control decreased as the delay between initial and terminal links increased. The results have implications for human choice situations where decisions are made between two immediately available reinforcement alternatives each associated with a different delayed outcome.

Short communication: rat's demand for group size.

Social isolation compromises the welfare of rats. However, it is not clear how many rats should be housed together under laboratory conditions. Pair housing, sometimes recommended over group housing, may help avoid aggression and disease transmission. Female rats, however, showed the highest average demand for a group size of 6 (versus 1, 2, 4, and 12) when stocking density was maintained at 20 cm2/rat. This finding contributes to work suggesting that rats should be group housed. This article shows that further studies are required into the actual risks of disease and injury associated with group versus pair housing.