[Real and hypothetical rewards in probability discounting]

In Experiment 1, undergraduates first made choices hypothetically between an uncertain large reward and a certain small reward, second they made choices with real money, and finally they again made hypothetical choices. The discounting rates in the first hypothetical reward condition were higher than those in the following conditions of real or hypothetical rewards. A significant difference in the discounting rate across conditions was not found when the real reward condition was replaced by the hypothetical reward condition (Experiment 2) or by the condition with probability contingency and hypothetical reward (Experiment 3). The difference in the discounting rate was replicated between the hypothetical and real reward conditions when the participants invested money when they selected an uncertain-large reward (Experiment 4). Johnson & Bickel (2002) found no difference in the discounting rate between hypothetical and real rewards when the real rewards were delivered to participants not during but after the experiment. The present experiments, by contrast, delivered real money immediately after every choice, and demonstrate that real and hypothetical rewards differ in the values of discounting rates.