A Laboratory Task to Assess Epistemic Mistrust: Behavioral Evidence for Mediation Between Childhood Trauma and Borderline Personality Features in Young Adults

Background Disruptions in epistemic trust have been recognised as key sequelae of trauma and as markers of vulnerability to borderline personality pathology. However, prior research has largely relied on self-reports and lacks behavioural measures of epistemic stance. The present studies introduce a novel behavioural task—the Balloon Analogue Risk Task for Epistemic Trust (BART-ET)—and examine its associations with borderline personality features, trauma history, and psychological distress. Methods Two cross-sectional studies were conducted with a combined sample of 273 young adults aged 18–25 (Study 1: N  = 120; Study 2: N  = 153). Participants completed self-report measures of borderline personality features (PAI-BOR) and epistemic trust, mistrust, and credulity (ETMCQ). Study 2 additionally included the Childhood Trauma Questionnaire (CTQ) and the Brief Symptom Inventory (BSI-GSI). All participants completed the BART-ET in a laboratory setting, which operationalised epistemic stance as the degree of deviation from a confederate experimenter’s advice during a risk-taking task. Analyses involved correlational tests and structural equation modelling (SEM) to evaluate the hypothesised associations and mediation effects. Results Across both samples, higher levels of borderline personality traits were associated with greater epistemic mistrust—both behaviourally (on the BART-ET) and via self-report (ETMCQ)—and with greater epistemic credulity, but not with epistemic trust. Behavioural and self-report measures of mistrust were significantly correlated, supporting the BART-ET’s convergent validity as an index of epistemic stance. In Study 2, childhood trauma exposure was positively associated with borderline features and with epistemic mistrust (but not significantly with epistemic trust or credulity). SEM analyses indicated that epistemic mistrust partially mediated the association between childhood trauma and borderline personality features. Conclusions This research provides the first behavioural evidence linking epistemic mistrust with borderline personality features and childhood trauma in young adults. The findings highlight that high epistemic mistrust—rather than a simple absence of trust—is a social-cognitive process potentially underlying personality vulnerability. The results also support the utility of the BART-ET as a novel behavioural tool for studying epistemic stance in clinical contexts.