People who identify more intensely with a political tribe or ideology share an underlying psychological trait: low levels of cognitive flexibility, according to a new study.
This "mental rigidity" makes it harder for people to change their ways of thinking or adapt to new environments, say researchers. Importantly, mental rigidity was found in those with the most fervent beliefs and affiliations on both the left and right of the political divide.
The study of over 700 US citizens, conducted by scientists from the University of Cambridge, is the largest - and first for over 20 years - to investigate whether the more politically "extreme" have a certain "type of mind" through the use of objective psychological testing.
The findings suggest that the basic mental processes governing our ability to switch between different concepts and tasks are linked to the intensity with which we attach ourselves to political doctrines - regardless of the ideology.
"Relative to political moderates, participants who indicated extreme attachment to either the Democratic or Republican Party exhibited mental rigidity on multiple objective neuropsychological tests," said Dr Leor Zmigrod, a Cambridge Gates Scholar and lead author of the study, now published in the Journal of Experimental Psychology.
"While political animosity often appears to be driven by emotion, we find that the way people unconsciously process neutral stimuli seems to play an important role in how they process ideological arguments."
"Those with lower cognitive flexibility see the world in more black-and-white terms, and struggle with new and different perspectives. The more inflexible mind may be especially susceptible to the clarity, certainty, and safety frequently offered by strong loyalty to collective ideologies," she said.
The research is the latest in a series of studies from Zmigrod and her Cambridge colleagues, Dr Jason Rentfrow and Professor Trevor Robbins, on the relationship between ideology and cognitive flexibility.
Their previous work over the last 18 months has suggested that mental rigidity is linked to more extreme attitudes with regards to religiosity, nationalism, and a willingness to endorse violence and sacrifice one's life for an ideological group.
For the latest study, the Cambridge team recruited 743 men and women of various ages and educational backgrounds from across the political spectrum through the Amazon Mechanical Turk platform.
Participants completed three psychological tests online: a word association game, a card-sorting test - where colours, shapes and numbers are matched according to shifting rules - and an exercise in which participants have a two-minute window to imagine possible uses for everyday objects.
"These are established and standardized cognitive tests which quantify how well individuals adapt to changing environments and how flexibly their minds process words and concepts," said Zmigrod.
The participants were also asked to score their feelings towards various divisive social and economic issues - from abortion and marriage to welfare - and the extent of "overlap" between their personal identity and the US Republican and Democrat parties.
Zmigrod and colleagues found that "partisan extremity" - the intensity of participants' attachment to their favoured political party - was a strong predictor of rigidity in all three cognitive tests. They also found that self-described Independents displayed greater cognitive flexibility compared to both Democrats and Republicans.
Other cognitive traits, such as originality or fluency of thought, were not related to heightened political partisanship, which researchers argue suggests the unique contribution of cognitive inflexibility.
"In the context of today's highly divided politics, it is important we work to understand the psychological underpinnings of dogmatism and strict ideological adherence," said Zmigrod.
"The aim of this research is not to draw false equivalences between different, and sometimes opposing, ideologies. We want to highlight the common psychological factors that shape how people come to hold extreme views and identities," said Zmigrod.
"Past studies have shown that it is possible to cultivate cognitive flexibility through training and education. Our findings raise the question of whether heightening our cognitive flexibility might help build more tolerant societies, and even develop antidotes to radicalization."
"While the conservatism and liberalism of our beliefs may at times divide us, our capacity to think about the world flexibly and adaptively can unite us," she added.