遅延価値割引課題おける「非系統的反応」の実態

–報酬金額と遅延時間の変化を通して–

抄録

The delay discounting task measures how people devalue rewards as the delay to receiving them increases. Typically, the subjective value of rewards decreases as delay time increases, resulting in a hyperbolic discounting curve. However, a large amount of unsystematic data has been reported on the delayed discounting task. In this study, we focused on the non-systematic responses that occur within each trial, as opposed to the non-systematic data that occur across the trial. We evaluated six reward amounts ranging from Y1,000 to Y100,000,000 and nine delay times ranging from one week to 70 years. The following four results were obtained. (1) When all trials of the task were conducted with a variety of reward amounts and delay times, over-discounting, non-discounting, and inconsistent responses were observed as well as typical responses. (2) We found that 90% of the data showed typical delay discounting for reward amounts up to Y10,000 and delay times up to one month. (3) Over-discounting tended to increase in frequency of occurrence as the delay time to reward increased, with a particularly sharp increase after 10 years in the condition of more than Y1,000,000. (4) The frequency of occurrence of no-discounting and inconsistent was low, regardless of condition.