Fig. 1.

Task Design. Trials started with a screen showing the choice options (see panel A). One option, the safe option, was always a sure $5. The other option, the risky option, was a chance of winning zero dollars or a high amount of money varying between $3 and $76. Chances of winning the high amount of money (in red) varied between 20% and 80% (see panel B). For the ambiguous choices, part of the bar was occluded thereby introducing uncertainty about the chances of winning. Ambiguity levels varied between 0%−80% (see panel C). The example in the figure reflects all ambiguity levels for a trial in which the chance of winning the high amount (shown in red) was 60%. In the solo condition, participants made choices without availability of additional information about a peer’s choice. In the social conditions, participants saw a picture of a peer and their choice, displayed as a green bar over the selection. Trials in the social safe condition were defined as all trials on which peer selected the safe option, whereas trials in the social risky condition were defined as trials in which the peer selected the risky option. Peers were the same gender and age category as the participants. The example displays an 18–22-year-old male. After the trial onset, participants indicated their choice within 4 s, their choice was displayed for 0.5 s and trials ended with a variable jitter.