Developmental emergence of complex prosocial motives and their influence on risky decision making

Humans hold beliefs about others’ preferences, which can inform a range of decisions including those involving risk. However, the accuracy of these beliefs, and the weight placed on our own preferences versus someone else’s for a decision that impacts both individuals, remains poorly understood. It is particularly relevant to characterize the role of beliefs about peer preferences in decision making during adolescence, a phase of the lifespan where peers take on a heightened importance and have an outsize impact on risky decisions. Using a sample of typically developing friend dyads (N=128, 12.0-22.8 years), we collected fully mutual data on decision preferences in an economic risky decision making task with safe (certain) and risky (more variable outcomes) options that varied in their expected value. We modeled the adjudication between one’s own and friend’s outcome with a modified expected utility model and characterized age-related changes with Generalized Additive Models. On average, participants overestimated their friend’s preference for risky choices across the full span of ages that were tested. In addition, we analyzed age-related changes in decision making for risky choice scenarios in which one of the two individuals must receive a nonpreferred option, both when following their genuine preferences and when taking the perspective of their friend. Participants aged 16-22 years weighed their friend’s outcome more, and earned less, when taking their friend’s perspective compared to their own. Young adults were willing to shield their friends from unwanted risks even when no monetary incentive was on the line. Together, these findings highlight late adolescence to early adulthood as a heightened period for prosocial considerations.