Figure 1.

Experimental tasks. In both tasks, subjects chose between a free small reward (SR) option, represented by a 1-star card, and a costly large reward (LR) option, represented by a 3-star card. In the effort task (a), the LR required an indicated number of squeezes (2, 4 or 6) on a hand dynamometer exceeding 50% of the individuals' max. strength. The SR required no effort production. In the delay task (b), the LR required waiting an indicated number of seconds (4, 7 or 10), whereas the SR was provided immediately. Blue cards indicate options available for selection, white cards indicate unavailable SRs. The left panels show the possible courses of a standard trial. Note that, following a choice of the LR option, the SR option remained available throughout the effort execution/delay phase and subjects could still abandon the LR option at any time. The right panels show the possible courses of a precommitment trial. Here, subjects first decided whether to precommit to the effort-requiring/delayed LR by making the SR unavailable for the current trial (see right panel, left column). If they decided against this voluntary restriction of their choice set, the trial continued identically to the standard trial (right panel, right column). The frame around the text displayed during the pre-choice precommitment phase is for illustration purposes only and was not present during the task. See main text for further explanations.