In the physical effort task, participants exerted one of six levels of force on a hand-held dynamometer (SS25LA, BIOPAC Systems) using their dominant hand (Fig. 1 C,D; Chong et al., 2018a (link); Atkins et al., 2020 (link)). At the beginning of the experiment, we determined individuals’ maximum voluntary contraction (MVC), which was defined as the maximum of three consecutive ballistic squeezes. To standardize effort requirements across participants, we defined the target effort levels for each individual as a function of their MVC (4–44%, in increments of 8%). Target levels were depicted as a horizontal yellow line on a vertical bar, and participants received real-time visual feedback of their applied force.
Each trial in the physical effort task commenced with a red pie chart, which cued the level of physical effort required on that trial. Participants then had to initiate and maintain their contraction above the required effort level for ≥50% of the total trial duration to be successfully rewarded. The physical effort task was identical to the cognitive effort task with respect to trial durations (10 s per effort level); number of trials per effort level; and overall block structure. The physical effort task was implemented on Psychtoolbox (Psychtoolbox.org">http://Psychtoolbox.org ) in MATLAB (The MathWorks).
Each trial in the physical effort task commenced with a red pie chart, which cued the level of physical effort required on that trial. Participants then had to initiate and maintain their contraction above the required effort level for ≥50% of the total trial duration to be successfully rewarded. The physical effort task was identical to the cognitive effort task with respect to trial durations (10 s per effort level); number of trials per effort level; and overall block structure. The physical effort task was implemented on Psychtoolbox (
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