Fig. 1.

The experimental task: (a) the trial sequence and (b) grouping of pain levels. In each trial (a), participants first saw the financial endowment for that trial and then received a single exemplar of painful electric shock, of low, medium, or high intensity. (Participants were not informed, nor did they report, that the pain was always at one of only three discrete levels.) They then selected the maximum price they were prepared to pay to avoid 15 additional shocks. The maximum price they could offer was their full endowment, which was given on a strictly trial-by-trial basis (such that there was no sense that endowments could be “saved” or carried over to pay for later pain relief). The market price was set randomly between zero and the full endowment amount, and if this price was lower than the participant’s price offer, the 15 painful stimuli were omitted at the cost of the market price (and not the participant’s offer). Trials were grouped into low-medium, high-medium, and low-high blocks (b). We repeated each block twice, so there were six blocks and 60 trials in total. The order of pain levels within each block was randomized, as was the overall order of the blocks.