Fig. 1.

a Schematic of gambling task. Top row fluid gambling task. Subjects were initially presented with a blank screen. Following a 3-s delay, two targets appeared. Both targets were the identical. Subjects could then choose one of the two targets by pressing either the left or the right key on the keyboard. Following the choice, a fluid reward was presented into the subject’s mouth via a juice tube. Trial was then followed by a short delay. Bottom row monetary gambling task. Task was identical to the fluid task, except the targets were a different color, and the reward was announced via text on the monitor, but was not given immediately. Trial types were switched at random in blocks of 10 trials. b Population data for discrimination ability for juice volumes. Subjects performed a two-alternative forced-choice task in which they had to identify the larger of the two juice volumes. Accuracy increased as the relative size of the two squirts increased. The two vertical lines indicate the relative values used in the low and high-risk conditions of the gambling task