Online interaction turns the congeniality bias into an uncongeniality bias

Online phenomena like echo chambers and belief polarisation are believed to be driven by humans’ penchant to selectively expose themselves to attitudinally congenial content. However, if like-minded content were the only predictor of online behaviour, heated debate and flaming on the Internet would hardly occur. Research has overlooked how online behaviour changes when people are given an opportunity to reply to dissenters, potentially turning a preference for attitudinally congenial information into a preference for uncongenial information. Three main experiments consistently show that in a discussion forum setting where users can respond to earlier posts, larger conflict between user attitude and post attitude predicts higher likelihood to respond. The effect of conflict on response behaviour is shaped by the attitudinal composition of the forum, and it also predicts subsequent polarisation of users’ attitudes. These results suggest that belief polarisation on social media can be driven by conflict rather than congeniality.