Exploring the malleability of self-bias in social contexts: Effects of interpersonal relationship, group membership, and social presence.

The self-bias effect, characterized by the prioritization of self-related information in cognitive processing, is well-documented, yet its flexibility within social contexts remains underexplored. This study examined how interpersonal relationships (cooperation vs. competition), group membership (ingroup vs. outgroup), and mere social presence modulate self-bias in task performance. In three experiments, participants completed a shape-label matching task in which geometric shapes were arbitrarily associated with self, partner, or stranger identities. Perceptual sensitivity (d') and reaction times (RTs) were analyzed to assess self- and partner bias across social conditions. Results demonstrated that self-bias was selectively malleable: Competition significantly enhanced self-bias in d', whereas cooperation had no effect. Additionally, self-bias was more pronounced in the presence of an outgroup partner compared with an ingroup partner. By contrast, mere social presence did not alter self-bias, indicating that passive copresence alone is insufficient to modulate self-prioritization. RTs remained unaffected by social context, suggesting that social influences primarily impact perceptual sensitivity rather than processing speed. Partner bias was consistently observed across all experiments but remained unaffected by social contexts, implying that while brief interaction is enough to establish a basic level of social relevance, stronger social engagement may be required to further modulate partner-related processing. These findings suggest that self-bias is selectively malleable, responding to contexts that accentuate self-other distinctions, while remaining robust against cooperative incentives or passive copresence, and highlighting the stability of partner bias in minimal social contexts. (PsycInfo Database Record (c) 2025 APA, all rights reserved).