Date of Award

6-2009

Degree Name

Master of Arts

Department

Psychology

First Advisor

Dr. Cynthia Pietras

Second Advisor

Dr. Lisa Baker

Third Advisor

Dr. Wayne Fuqua

Access Setting

Masters Thesis-Campus Only

Abstract

Three experiments investigated probability discounting in 18 adult humans when outcomes were hypothetical or real. Participants were given repeated choices between a large amount ($1.00) delivered probabilistically and a smaller amount delivered with certainty (e.g. $0.05). The value of the certain option was adjusted across trials to determine an indifference point between the two options. Experiment 1 used a decreasing-adjustment algorithm (Du, Green, & Myerson, 2002). Experiments 2 and 3 used a double-limit algorithm (Richards, Zhang, Mitchell, & de Wit, 1999). Probabilities of the large option were manipulated across blocks to obtain a range of indifference points. In hypotheticalreward conditions, participants were paid a standard amount and in real-reward conditions, participants were paid the outcomes of their choices from a proportion of trials each session. Experiment 3 included post-session feedback on average trial earnings. A repeated measurements design was used and all participants were exposed to both hypothetical- and real-reward conditions. Hyperbolic discounting curves were fit to indifference points and discounting rates were estimated. Area under the curve values were also calculated. Probability-discounting rates differed across the first hypotheticaland first real-reward conditions in Experiments 1 and 2. Experiment 1 participants were more risk prone in the first real-reward condition than in the first hypothetical-reward condition, whereas Experiment 2 participants were more risk averse in the real-reward condition. No differences in probability-discounting rates were found in Experiment 3. These results suggest that the nature of the choice outcome may influence probability discounting, but that the effect may depend on the adjusting algorithm and procedure used.

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