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| Delay Discounting |
| Monday, May 28, 2007 |
| 9:00 AM–10:20 AM |
| Madeleine AB |
| Area: EAB/BPH; Domain: Basic Research |
| Chair: Amy Odum (Utah State University) |
| Abstract: This symposium highlights recent work in delay discounting, the study of how the present value of an outcome is degraded by delay to its receipt. In the first presentation, Mazur will present data from rats choosing between single and multiple delayed food reinforcers. Baumann and colleagues will next discuss discounting by humans of different types of hypothetical outcomes that differ in whether they are directly or indirectly consumed or exchanged for other things. For the third talk, Green and colleagues will compare discounting of three directly consumable hypothetical outcomes with money. In the last talk, Johnson and colleagues will discuss discounting of different outcomes by regular marijuana users and matched control participants. |
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| Rat’s Choices between Single and Multiple Delayed Reinforcers. |
| JAMES E. MAZUR (Southern Connecticut State University) |
| Abstract: Rats chose between alternatives that differed in the number of reinforcers and in the delay to each reinforcer. A left lever press led to two reinforcers, each delivered after a fixed delay. A right lever press led to one reinforcer after an adjusting delay. The adjusting delay was increased or decreased many times a session, depending on the rat’s choices, so as to estimate an indifference point—a delay at which the two alternatives were chosen about equally often. The results were compared to those from a previous experiment with pigeons that used a similar procedure (Mazur, 1986). The data from the present experiment were qualitatively similar to the pigeons’ data, but quantitative differences suggested that the rats were less sensitive to delay of reinforcement than pigeons. The overall pattern of results was well described by the hyperbolic-decay model, which states that each additional reinforcer delivered by an alternative increases preference for that alternative, but that a reinforcer’s effect is inversely related to its delay. |
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| To Eat, Not to Eat, or to Exchange: Discounting of Food, Gasoline, and Money. |
| ANA A. BAUMANN (Utah State University), Adam Kynaston (Utah State University), Jane K. Alder (Utah State University), Amy Odum (Utah State University) |
| Abstract: Delay discounting determines how the value of the outcome is affected by the delay to its receipt. Research to date has shown that consumable outcomes (e.g., alcohol) are discounted more steeply than the non-consumable outcome money. We are investigating the generality of this effect by comparing discounting of food (directly consumed), gasoline (indirectly consumed), and money (not consumed but exchanged for other things). Human participants completed a computer-based titration procedure to estimate the degree of discounting for hypothetical outcomes at seven different delays. Each participant completed the assessment for all three outcomes separately. The data indicate that food and gasoline are both discounted more steeply than money. The degree of discounting for gasoline is intermediate to that of food and money. These results suggest that steeper discounting of consumable outcomes than money is a general phenomenon, extending to indirectly consumed alternatives like gasoline. |
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| Discounting of Monetary and Directly Consumable Rewards. |
| LEONARD GREEN (Washington University), Joel Myerson (Washington University), Sara J. Estle (Washington University, St. Louis), Daniel D. Holt (Washington University) |
| Abstract: We compared temporal and probability discounting of a non-consumable reward (money) and three directly consumable rewards (candy, soda, beer). Delayed monetary rewards were discounted less steeply than the directly consumable rewards, all three of which were discounted at equivalent rates. When rewards were probabilistic, however, there was no difference between the discounting of monetary and directly consumable rewards. It has been reported that substance abusers discount delayed drug rewards more steeply than money, but this difference either may reflect special characteristics of drugs and/or drug abusers, or it may reflect a general property of consumable rewards (Odum & Rainaud, 2003). The present findings suggest that abused substances (like beer) share the properties of other directly consumable rewards, whereas delayed monetary rewards are special because they are fungible, generalized (conditioned) reinforcers. |
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| Delay Discounting in Marijuana-Dependent Individuals. |
| MATTHEW W. JOHNSON (Johns Hopkins University School of Medicine), Warren K. Bickel (University of Arkansas for Medical Sciences), Forest J. Baker (Duke University), Brent A. Moore (Yale University School of Medicine ), Gary J. Badger (University of Vermont ), Alan J. Budney (University of Arkansas for Medical Sciences) |
| Abstract: A growing number of studies have found that a variety of drug dependent groups (e.g., those dependent on nicotine, opioids, alcohol, and cocaine) discount or devalue delayed rewards significantly more than matched-control participants. The present study sought to extend these findings to marijuana dependence. Dependent marijuana users were compared to ex-dependent marijuana users and matched-controls. Participants in both groups performed computer tasks that assessed delay discounting for a hypothetical $1000 reward, a duration of improved health subjectively equivalent to receiving $1000, and an amount of marijuana subjectively equivalent to receiving $1000. No significant differences were detected in money or health discounting among the marijuana dependent individuals, ex-dependent individuals, and controls. Likewise, no significant differences were found in money, health, and marijuana discounting within the marijuana dependent group. These results may suggest a boundary condition for the link between rapid delay discounting and drug dependence. |
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