Belief Updating and Argument Evaluation

Studies of how evidence affects beliefs sometimes show belief polarization in response to mixed evidence. However, the nature of the mental processes leading to change in opinion is up for debate. Different accounts of how people process evidence and then update their beliefs make different predictions, especially about one-sided evidence, which is rarely examined. We presented subjects with multiple text arguments regarding socio-political topics as one-sided or mixed evidence. Participants rated arguments differently according to their extant beliefs, which is consistent with accounts of motivated reasoning. They did not polarize afterward, instead showing evidence of belief updating according to Bayesian principles: belief change is sensitive to prior opinions and to the direction and quality of the evidence presented. These data support rethinking some of the mental processes underlying incorporation of evidence into a personal belief structure.