More Efficient Evaluation, Not a Simple Bias, Underlies Trust in Friends Across the Adult Life Span

Objectives: Socioemotional Selectivity Theory suggests that the emotional significance of social partners should have a greater influence on older adults' choices, potentially leading them to weigh social relationships more heavily when deciding whom to trust. We tested whether this preferential trust in closer relationships stems from a preexisting bias (predisposition) or more efficient information processing (evaluation) and how these processes change across the adult life span. Methods: In a sample of 163 healthy adults (ages 18–80), we applied a diffusion decision model (DDM) to behavioral data from an economic trust game. Participants made investment decisions with a friend, a stranger, and a computer partner. Results: Participants invested more in friends than in strangers. The DDM revealed this was driven by a higher rate of evidence accumulation (drift rate, v) for friends, not a shift in response bias (starting point, z). Age was positively correlated with non-decision time (t), reflecting general slowing, but was not associated with other parameters. The evaluative enhancement for friends was preserved across the life span. Discussion: Preferential trust in close others arises from more efficient evaluative processing, not a simple predisposition. This core social-cognitive mechanism remains preserved in older adulthood, underscoring the value of cognitive modeling for uncovering information-processing mechanisms that support socioemotional priorities as people age.