Recently encountered delay lengths produce contrast effects on delay discounting

People demonstrate shallower delay discounting when they have recently made decisions about smaller amounts of money than when they have recently made decisions about larger amounts of money. That is, recent reward amounts produce a contrast effect on delay discounting. We tested whether a similar contrast effect occurs for delays. We recruited two groups of participants via Mechanical Turk. The shorter-delay group made choices about delays ranging from one day to one month, and the longer-delay group made choices about delays ranging from 14 months to 30 years. Both groups then made choices about the same, intermediate delays (one week to 21 months); the longer delay group showed significantly shallower delay discounting, indicating a contrast effect. This suggests that delay discounting is affected not just by absolute delay length, but by the relative delay length.