Abstract
The immediacy of a consequence and the effort required to achieve it are two key factors that influence decision-making. Although studies have examined the effects of delay, and cognitive and physical effort on choice behaviour separately, few have explored how these factors interact. The current study arranged two computer tasks where 170 participants needed to obtain a number of points. One task assessed physical effort (precise clicking), the other assessed cognitive effort (addition mathematic problems). Both tasks arranged a 24-s fixed interval schedule for reward with two levels of response effort. During most trials, participants could defect to a smaller immediate reward after various delays. There were significant effects of delay and effort in both tasks. Participants chose the larger later reward more often when the opportunity to defect was more delayed and when response effort was greater. There were significant correlations between individuals’ discounting of physical and cognitive effort at short and medium length delays, suggesting effort discounting is trait-like. Two groups, one scoring high (N = 20) and the other scoring low (N = 58) on measures of ADHD, were separated from the sample. The ADHD group showed differences in the effects of effort compared to controls with lower response rates. They also showed no change in choice proportions for the larger later reward when effort level changed, while controls did. Changes in task effort might be processed differently in ADHD which impacts decision-making for rewards. There were no differences in effects of delay between groups. Both delay and effort should be considered in designing tasks (e.g., educational or workplace settings), delayed rewards and thresholds where rewards are significantly devalued should be avoided.