Whether it’s propaganda or hustling, it’s often said that a major part of persuading people is to act and speak with complete conviction in what you’re saying.  The logic goes that your confidence in your words will convince others to go along with you.

It’s not a heuristic that new research from University College London believes is necessarily true.  The research, which involved scanning the brain of participants, suggests instead a new form of confirmation bias that can render it almost impossible to change people’s opinions.

“We found that when people disagree, their brains fail to encode the quality of the other person’s opinion, giving them less reason to change their mind,” the researchers say.

Powers of persuasion

Volunteers were split into pairs and asked to estimate the price of houses, with each person betting a certain amount depending on whether the price was more or less than a particular amount.  The bets were largely done on the level of confidence each person had in their prediction.

Each person was also asked to lay in an MRI scanner during this process, with the two scanners divided by a glass partition.  They were shown the properties again and reminded of their initial judgement, before being shown the assessment of their partner and the wager they placed on it.  Finally, they were asked to submit their final bet on the price of the property.

The results revealed that when both parties agreed, the bets placed would typically increase, with it common for the partners to almost egg each other on with their confidence.  When they disagreed, however, the partner had minimal impact on the bets placed, even if the disagreeing partner had made a large bet on their choice.

The data suggests that the posterior medial prefrontal cortex (pMFC) was especially active in this period of incorporating another person’s beliefs into one’s own.  There were distinct differences in activity in the area depending on the scale of the partner’s bet when that bet agreed with their own choice.  When the partners disagreed, however, there was no such link between the scale of the partner’s bet and activity in the pMFC area.

Decision making

The pMFC has already been established as a key part of the brain when it comes to making decisions, and especially when it comes to changing decisions already made.

The researchers express concern that this tendency to ignore the strength of opposing points of view may result in polarization and the maintenance of wholly false beliefs.

“Our findings could help make sense of some puzzling observations in domains including science and politics,” they say.  “For instance, over the last decade climate scientists have expressed greater confidence that climate change is man-made. Yet, the percentage of the population that believe this notion to be true has dropped over the same period of time. While there are complex, multi-layered reasons for this specific trend, such examples may be related to a bias in how the strength of other’s opinions are encoded in our brains.”