Basis functions for social decision-making develop during adolescence

Adolescents learn to navigate increasingly complex social environments, where flexible and efficientcognitive mechanisms are needed to behave adaptively. Prominent theories of cognitive maturation suggestthat adolescents’ decision-making is noisier than adults’ and that their decisions can be swayed by irrelevantinformation. By contrast, here, we suggest that cognitive development also allows them to increasingly usecombinatorial representations of social input. This manifests in emergent use of abstract social basisfunctions across adolescent development. Social basis functions represent combinations of individuals’interactions (e.g., patterns of cooperation and competition) and allow for efficient information compression.In a novel in-person group decision-making experiment with adolescents (n = 50) and young adults (n =50), we confirmed a counterintuitive set of predictions derived from the basis function model: Adults mademore accurate decisions than adolescents, but, in parallel, they increasingly made a specific type of decisionerror more frequently than adolescents. They ‘mixed up’ relevant and irrelevant players as a function of thegroup structure of the task. Using multi-attribute drift diffusion modelling, we show that the observed agedifferences are consistent with a stronger influence of the group structure during social decision-making inadults. Together, these findings suggest that cognitive development during adolescence involvesfundamental shifts in the use of abstract social representations generally and in the use of combinatorialsocial basis functions in particular.