The boundaries and ontogeny of myside bias

When we believe something, we favor information supporting that belief, a myside bias. Despite decades of research showing its influence on reasoning, we lack a clear understanding of how context and age influence this bias. We examined how the presence versus absence of an argumentative context shifts information seeking in 484 participants aged 5-55. After making a prediction, participants were tasked with learning whether their prediction was correct or told that they would need to convince another person that their prediction was correct at the end of the experiment. Half were told that another person made a conflicting prediction; half received no information about the other person's beliefs. Participants selected envelopes as information samples, containing information supporting or undermining their predictions. Having to convince someone in the future biased information seeking. This bias increased and changed across the lifespan: 5-year-olds selected positive information supporting their predictions. From age 11, participants selected a more balanced set of self-favoring evidence: positive information supporting their prediction and counterevidence undermining the alternative. The impact of a conflicting perspective depended on the goal. When the goal was convincing, conflict increased information seeking and slightly reduced the bias. When the goal was learning, conflict reduced information seeking and slightly increased the bias. In sum, we showed that myside bias is influenced by the presence of an argumentative context, that is, primarily by the aim of convincing someone in the future and to some extent by the presence of a conflicting perspective, and increases with age. (PsycInfo Database Record (c) 2026 APA, all rights reserved).