Figure 1.

Task Design

Participants were first trained on (A and B) a cognitively effortful task and (C and D) a physically effortful task before (E) indicating their preference for investing effort for reward.

(A) The cognitive effort task required participants to monitor one to six RSVP streams for a target letter (“T”).

(B) Each trial began with a blue pie chart indicating the number of streams they had to monitor on that trial. After completing each effort level, participants received feedback on their performance. Each trial lasted 10 s.

(C) The physical effort task required participants to sustain variable amounts of force on a hand-held dynamometer, with the target levels of force defined as a function of each individual’s maximum voluntary contraction (MVC) (4%, 12%, 20%, 28%, 36%, and 44%).

(D) Each trial began with a red pie chart indicating the amount of force they had to apply on that trial. Trial durations were identical to those for the cognitive effort task (10 s). At the conclusion of each trial, participants received feedback on their performance.

(E) The choice phase required participants to decide how much effort they were willing to invest for reward. The choice was always between a fixed baseline option (the lowest level of effort for the lowest reward; one point) and a variable high-effort/high-reward offer (higher levels of effort; rewards of two to ten points). Separate choices were made for cognitive and physical effort.