Beyond mere novelty: Categorization drives differentiation.

Stereotype formation is shaped by differentiation, that is, the tendency to prioritize attributes that render a novel group distinct from comparison groups. While differentiation is well documented, it remains unclear whether it is intrinsic to categorization or whether it is a byproduct of a general processing advantage of novel stimuli. We conducted three preregistered experiments to disentangle these accounts. In all experiments, participants learned a set of social traits that were either assigned to a single group or distributed across two groups. Crucially, novel traits presented in the second half of the stimulus set marked intergroup distinctiveness only in the two-groups condition while being equally novel in the single-group condition. In line with a category-based account of differentiation, recall for novel traits was enhanced in the two-groups condition compared to the single-group condition (Exp. 1 & 3) and an additional control condition without groups (Exp. 3). Moreover, novel traits were judged as more typical for their group than initially learned traits, but only in the two-groups condition (Exp. 2). These findings suggest differentiation is not a fixed response to novelty but a genuine categorization effect, serving a functional role in distinguishing groups. We discuss implications for category learning and stereotype formation.