Haas put 58 people with diverse political views in a brain scanner. On each trial, participants were asked whether it was good or bad that a candidate held a position on a particular issue and not whether they personally agreed or disagreed with it. Framing the task that way allowed the researchers to look at neural processing as a function of whether the information was expected or unexpected—what they termed congruent or incongruent. They also considered participants’ own party identification and whether there was a relationship between ideological differences and how the subjects did the task.

Liberals proved more attentive to incongruent information, especially for Democratic candidates. When they encountered such a position, it took them longer to make a decision about whether it was good or bad. They were likely to show activation for incongruent information in two brain regions: the insula and anterior cingulate cortex, which “are involved in helping people form and think about their attitudes,” Haas says. How do out-of-the-ordinary positions affect later voting? Haas suspects that engaging more with such information might make voters more likely to punish candidates for it later. But she acknowledges that they may instead exercise a particular form of bias called “motivated reasoning” to downplay the incongruity.