Event Source Modulates the Valence Focus of Optimism Bias: Evidence from Behavior and ERPs

Background: Optimism bias is the tendency to expect more positive and fewer negative events for themselves versus for others. However, it remains unclear whether the valence focus of this bias depends on how events unfold (i.e., through autonomous choice vs. external imposition). This study used behavioral and ERP measures to investigate how the event source modulates the valence focus of optimism bias. Methods: Thirty participants completed a 2 (event source: autonomous choice vs. external imposition) × 2 (valence: positive events vs. negative events) × 2 (target: self vs. other) task while an EEG was recorded. The late positive potential (LPP) was analyzed as a neural index of self-relevance. Results: Behaviorally, autonomous choice preserved optimism bias for positive events (self > other, p = 0.023), whereas external imposition induced it for negative events (self < other, p = 0.006). Under autonomous choice, the LPP mirrored this pattern (enhanced for self-positive events, p = 0.038). Under external imposition, the LPP showed only a valence-general self-bias (main effect of target, p = 0.014). Conclusions: These preliminary findings suggest that event sources may influence the valence focus of optimism bias. Under autonomous choice, the bias is positive-focused. Under external imposition, it shifts to negative-focused. This dissociation between behavioral and neural patterns is consistent with dual patterns in optimism bias expression, though further research is needed.