**A**, In each trial, participants viewed a stimulus pair providing information about the probability of winning [p(win)] on that trial. Then they chose between a large (8 points) and a small bet (2 points) by pressing a button corresponding to the side of the screen containing their preference. Feedback was provided as a green box surrounding the wager amount if the participants won the bet and as a red box if the participant lost. **B**, The stimulus pair to be presented on each trial was randomly selected from a set of 20 possible pairs formed from 5 different novel symbols, labeled A, B, M, Y, Z here. Each stimulus pair was associated with a probability of winning [p(win)] for that trial as annotated and color-coded in the figure, ranging from red to green as p(win) increases. The p(win) associated with each pair was calculated as an adjustment from 50% determined by each symbol (+0.3, +0.15, 0, −0.15 and −0.3, for A, B, M, Y and Z, respectively. See Materials and Methods section for detail). Over the course of a block of 20 trials each symbol was paired twice with each one of the other symbols, and symbols were never paired with themselves. **C**, As result of the design, feedback conveyed information about the valence (gain versus loss) and magnitude (large versus small) of the outcome on the current trial. Feedback also conveyed information about value of the feedback compared to the outcome that “would-have-been” if the alternative decision had been made (relative outcome: worst versus best).

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