Decomposing the effort paradox in reward processing: Time matters

Abstract Effort expenditure not only discounts reward value prospectively but also accrues reward value retrospectively. To decompose the effort paradox in reward processing, the current event-related potential study investigated the neural dynamics underlying effects of effort expenditure on subsequent reward processing. Participants exerted one of two levels of effort to obtain an opportunity of winning a high or low amount of monetary reward, and we focused on electrophysiological activity during the anticipatory and consummatory phases of reward processing. During the anticipatory phase, the stimulus-preceding negativity was enhanced when potential high rewards were anticipated, but this reward effect disappeared following high-effort expenditure. During the consummatory phase, feedback-related ERPs were increased for high relative to low rewards, and this reward effect was enlarged following effort expenditure during the early stage (200–300 ms) as indexed by the reward positivity but not the late stage (400–600 ms) as indexed by the P3. Our findings provide a strong support for the psychological contrast theory and indicate that time matters in decomposing the effort paradox for reward processing such that effort expenditure reduces reward sensitivity during the anticipatory phase but enhances reward sensitivity during the consummatory phase.