Abstract.
Increasing political polarization in the United States has led individuals to process information in ways that reinforce their prior beliefs, often dismissing sources associated with opposing views or the other party. While partisan-motivated rea- soning provides a well-established explanation for this phenomenon, we investigate and document a largely overlooked determinant: the role of surprise in belief updating. Using two experimental studies, we exposed participants to identi- cal political information about the likely outcome of the 2024 presidential elec- tion, while varying its source, and measured belief updating via the Log-Likelihood Ratio. Results show that belief updating was primarily driven by the level of sur- prise, not source credibility. Counter-stereotypical signals —when a source provided unexpected information— elicited stronger updates, overriding partisan bias. Our findings suggest that surprise disrupts ideological echo chambers, challenging entrenched beliefs more effectively than source alignment alone.
