Probability Alters Delay Discounting, but Delay Does Not Alter Probability Discounting

Delay and probability discounting occur when the subjective value of an outcome changes because its delivery is either delayed or uncertain, respectively. Although theorists have argued whether these processes are one in the same or distinct, few studies have investigated if and how they interact. Experiment 1 had 191 university students complete a discounting task in which both the delay to and the probability of the outcome were varied across questions about a hypothetical romantic relationship. Experiment 2 replicated this procedure with 153 participants completing a discounting task with a hypothetical monetary amount as the outcome. Experiment 3 had 181 participants complete the discounting task about a hypothetical romantic relationship and measured discounting over an increased number of delays or probabilities. Results across all three experiments showed that rates of delay discounting changed as a function of probability; greater impulsive responding was observed as the likelihood of obtaining the outcome decreased. Rates of probability discounting were largely unaltered by the delay to receiving the outcome. The present results support the idea that delay and probability discounting are at least somewhat distinct. Furthermore, they suggest that the processes may differentially interact with one another.