Delay Discounting and the Cost of Waiting
If offered $50 now or $100 in a year, many of us will choose $50 now. This occurs because of delay discounting – the idea that reinforcers lose value over time. Individuals tend to display shallower discounting (self-controlled decision-making) in hypothetical discounting tasks, and steeper discounting (impulsive decision-making) in experiential discounting tasks. Hypothetical discounting tasks involve participants making a series of hypothetical monetary decisions (e.g. $50 now versus $100 in a year) over a range of delays. Experiential discounting tasks involve participants experiencing the delays and outcomes of their choices. A critical difference between hypothetical and experiential discounting tasks is the type of delay they use. Hypothetical discounting task delays typically involve postponing. This involves participants imagining the reward is delivered to them after the delay and that they are free to pursue other activities during the delay. Experiential task delays involve participants waiting out each delay before they receive their reward, (unable access any alternative reinforcement during the delay). Individuals discount more steeply when tested experientially than hypothetically. Experiment 1 investigated whether waiting and postponing are different discounting constructs. We achieved this via a 2 X 2 within-subjects design where both experiential and hypothetical discounting tasks had both Waiting and Postponing conditions. The hypothetical discounting task involved participants being instructed to imagine waiting for a reward after a delay (Waiting Condition), or imagine the reward would simply be delivered to them after the delay (Postponing Condition). The experiential task involved participants playing a video game that involved having to stop playing and wait for a larger number of points after a delay (Waiting Condition), or playing the game and getting the points delivered after the delay (Postponing Condition). We expected steeper discounting rates when waiting compared to postponing in both the experiential and hypothetical tasks. We found this effect only in the hypothetical task; however, this might be due to our procedure. We randomised the waiting and postponing trials in both tasks and this may have resulted in the participants being unable to discriminate between the interspersed trials. Experiment 2 investigated whether this methodological feature affected discounting in the experiential task, and we found that blocking the trials resulted in the anticipated effect. We found steeper discounting in both the experiential and hypothetical tasks for waiting compared to postponing after implementing this change, suggesting that waiting and postponing are different constructs. Experiment 3 investigated what drives the difference between waiting and postponing. We found that waiting has a greater effect on reward value than postponing due to the inability to access alternative reinforcement during the delay. We also investigated the relationships among our discounting measures and a measure of the consideration of future consequences, and a measure of delayed gratification. We found no correlation among discounting and these measures, and no consistent correlation between waiting and postponing. Overall, our results indicated that waiting and postponing are distinct constructs, and that the inability to access alternative reinforcement during a delay is the key difference between them.