Simulating Personal Wealth in the Laboratory.

During laboratory gambling tasks participants are not typically allowed to wager their personal wealth. Instead, wealth is simulated by telling participants they have been endowed with game tokens that will be later exchanged for money. Past research indicates that participants undervalue game tokens following this procedure, which leads to elevated risk taking compared to procedures that add saliency or realism to the monetary payoff. A between-subjects experiment tested whether showing a picture of money during the endowment instructions and repeating token-money exchange information during the session influenced participants' preference for risky and riskless options. The results showed no effect of the money picture. However, repeated token-money exchange information significantly decreased risk taking. Together with past studies, this finding suggests that endowment procedures might establish greater value in game tokens, and therefore better simulate personal wealth, when the eventual exchange between game tokens and money is made more salient to participants.

Laboratory simulated gambling: risk varies across participant-stake procedure.

This study investigated whether risk taking on a laboratory gambling task differed depending on whether participants gambled with earned or experimenter-provided game credits. Participants made repeated choices between two options, one to wager game credits on a game that produced probabilistic gains and losses, and one to gain game credits with certainty. Choice was investigated across stake and no-stake conditions and condition order was counterbalanced across conditions. Risk taking was higher under stake than no-stake conditions, but only when stake conditions were experienced first. There was no effect on risk taking of the amount of the certain gain. Results are consistent with previous research showing that participant-stake procedures promote greater risk taking than procedures that allow participants to gamble with their own earnings, and also show that experience gambling with earned credits has an enduring effect on risk taking.

Human responding on random-interval schedules of response-cost punishment: the role of reduced reinforcement density.

An experiment with adult humans investigated the effects of response-contingent money loss (response-cost punishment) on monetary-reinforced responding. A yoked-control procedure was used to separate the effects on responding of the response-cost contingency from the effects of reduced reinforcement density. Eight adults pressed buttons for money on a three-component multiple reinforcement schedule. During baseline, responding in all components produced money gains according to a random-interval 20-s schedule. During punishment conditions, responding during the punishment component conjointly produced money losses according to a random-interval schedule. The value of the response-cost schedule was manipulated across conditions to systematically evaluate the effects on responding of response-cost frequency. Participants were assigned to one of two yoked-control conditions. For participants in the Yoked Punishment group, during punishment conditions money losses were delivered in the yoked component response independently at the same intervals that money losses were produced in the punishment component. For participants in the Yoked Reinforcement group, responding in the yoked component produced the same net earnings as produced in the punishment component. In 6 of 8 participants, contingent response cost selectively decreased response rates in the punishment component and the magnitude of the decrease was directly related to the punishment schedule value. Under punishment conditions, for participants in the Yoked Punishment group response rates in the yoked component also decreased, but the decrease was less than that observed in the punishment component, whereas for participants in the Yoked Reinforcement group response rates in the yoked component remained similar to rates in the no-punishment component. These results provide further evidence that contingent response cost functions similarly to noxious punishers in that it appears to suppress responding apart from its effects on reinforcement density.

Effects of monetary reserves and rate of gain on human risky choice under budget constraints.

The energy-budget rule is an optimal foraging model that predicts that choice should be risk averse when net gains plus reserves meet energy requirements (positive energy-budget conditions) and risk prone when net gains plus reserves fall below requirements (negative energy-budget conditions). Studies have shown that the energy-budget rule provides a good description of risky choice in humans when choice is studied under economic conditions (i.e., earnings budgets) that simulate positive and negative energy budgets. In previous human studies, earnings budgets were manipulated by varying earnings requirements, but in most nonhuman studies, energy budgets have been manipulated by varying reserves and/or mean rates of reinforcement. The present study therefore investigated choice in humans between certain and variable monetary outcomes when earnings budgets were manipulated by varying monetary reserves and mean rates of monetary gain. Consistent with the energy-budget rule, choice tended to be risk averse under positive-budget conditions and risk neutral or risk prone under negative-budget conditions. Sequential choices were also well described by a dynamic optimization model, especially when expected earnings for optimal choices were high. These results replicate and extend the results of prior experiments in showing that humans' choices are generally consistent with the predictions of the energy-budget rule when studied under conditions analogous to those used in nonhuman energy-budget studies, and that choice patterns tend to maximize reinforcement.

Discriminative stimulus effects of gamma-hydroxybutyrate (GHB) and its metabolic precursor, gamma-butyrolactone (GBL) in rats.

RATIONALE: Gamma-hydroxybutyrate (GHB) is becoming an increasingly popular drug of abuse. Metabolic precursors of GHB, gamma-butyrolactone (GBL) and 1,4-butanediol (BDL), are commercially available industrial solvents that may also present potential health risks. Relatively little is known about the neurobehavioral effects of GHB and its precursors. OBJECTIVE: The aim of the present investigation was to characterize the discriminative stimulus effects of GHB and its precursor, GBL. METHODS: Male Sprague-Dawley rats were trained to discriminate GHB [300 mg/kg, i.g.; n=16] or GBL (150 mg/kg, i.p.; n=8) from vehicle under a fixed ratio 20 (FR 20) schedule of food reinforcement. Stimulus generalization tests were then conducted with several compounds. RESULTS: GHB and GBL produced cross-generalization and BDL was fully substituted for both GHB and GBL. Two benzodiazepines, alprazolam and diazepam, and the 5-HT1A agonist, buspirone, did not substitute for either training drug nor did ethanol or the NMDA antagonists, PCP and ketamine. The GHB antagonist, NCS-382, and the GABA(B) antagonist, CGP-35348, blocked the discriminative stimulus effects of GHB but not those of GBL. CONCLUSIONS: These findings suggest that GHB and its metabolic precursors produce similar subjective effects that differ from those of other sedative-hypnotic drugs. Further investigations into the neurochemical actions underlying the subjective effects of these drugs are warranted.

Up or down: the influence of upcoming reinforcement on consummatory and operant behavior.

Research has shown that animal subjects that are given a chance to consume a low-valued substance will consume less of it if a high-valued substance will soon be available than they would if the low-valued substance were to remain available (negative consummatory contrast). Research has also shown that subjects that lever press for a low-valued reinforcer will press the lever more often for that reinforcer if they will soon be able to lever press for a high-valued reinforcer than they would if they continue to press for the low-valued reinforcer (positive induction). The present study investigated these different changes in behavior across 3 experiments. The results suggest that the occurrence of contrast or induction does not depend on the type of substances that are used. We argue that further investigation of the contrast vs. induction issue is warranted because it has empirical, theoretical, and applied implications.