Are Republican and Democratic Brains Different?

A new study concludes that everyone uses reason to persuade, not to find truth.


People use reason to convince themselves, even in the face of evidence to the contrary, that their side is right and the other side is wrong. That's the conclusion of a new study by the Yale Cultural Cognition Project, an academic group that studies how cultural values shape public risk perceptions and related policy beliefs, headed by law and psychology professor Dan Kahan. To explore the sources of ideological polarization on subjects such as climate change, gun violence, and nuclear power, Kahan and his team devised and tested three theories:

The public irrationality thesis. Nobel Prize–winning economist Daniel Kahneman argues that humans employ two different cognitive systems to evaluate new information. The first uses fast rules of thumb—heuristics that are triggered by emotional reactions to new situations—while the second relies on slower, systematic reasoning. People adopt many rules of thumb from groups with whom they share cultural or ideological commitments. This theory implies that when people are challenged with new information or arguments, they find it quicker and easier to believe what their peers believe. 

The Republican brain hypothesis. This idea relies on research that shows a negative correlation between political conservatism and the traits of open-mindedness and critical reflection. Those findings suggest that conservative cognition asymmetrically relies on fast rules of thumb to make decisions and that conservatives are less likely than liberals to engage in cognitive reflection. Consequently, while liberals evaluate information with the aim of developing useful public policies, mule-stubborn conservatives dismiss discomforting scientific facts and spend their time just "standing athwart history yelling Stop."

The expressive rationality thesis. Perhaps beliefs about issues such as the riskiness of climate change or nuclear power constitute part of what it means for people to belong to specific groups. Shared beliefs form part of their identities. People assess new information so that their conclusions signal their trustworthiness and loyalty to social groups.

Both the public irrationality thesis and the Republican brain hypothesis claim that ideological polarization arises from overreliance on cognitive rules of thumb. In the case of expressive rationality, people who are good at cognitive reflection will be better able to rationalize their beliefs in the face of any contrary evidence. If liberals really are more inclined toward cognitive reflection, Kahan writes, that implies they "are all the more likely to succeed in resisting evidence that challenges the factual premises of their preferred policy positions."

The Yale researchers asked 1,600 Americans to place themselves on a continuum stretching from "strong Democrat" through "independent" to "strong Republican." Next they were asked if they considered themselves "very liberal," "liberal," "moderate," "conservative," or "very conservative." Once sorted by partisanship and ideology, the participants completed a short cognitive reflection test.

Then Kahan used something like this three-question cognitive reflection test devised by Massachusetts Institute of Technology researchers: 1) A bat and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much does the ball cost? 2) If it takes five machines five minutes to make five widgets, how long would it take 100 machines to make 100 widgets? 3) In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half the lake? (Answers below.)

Once participants had completed the cognitive reflection test, they were divided into three experimental groups. In the first group, subjects were told that "psychologists believe the questions you have just answered measure how reflective and open-minded someone is." In the second group, subjects were told that people who are not skeptical of climate change tended to get more answers correct. The third group was told the opposite, i.e., climate-change skeptics got more answers right. Then each group was asked how valid they thought the test was as a measure of open-mindedness.

Recent polling finds that conservatives are more likely than liberals to be skeptical about man-made global warming. Thus the Republican brain hypothesis would predict that right-wing subjects would be more inclined to see the cognitive reflection test as valid when told it suggests that climate-change skeptics are more open-minded. On the flip side, if left-wing subjects really are more natively reflective, their assessment of the test's validity should not depend much on the putative correlation between one's score and one's views regarding climate change. 

The public irrationality thesis predicts that motivated reasoning, i.e., jumping to conclusions congenial to one's social group, will be more common among people who score low on cognitive reflection, no matter their ideological biases. Unlike both the public irrationality and the Republican brain hypotheses, the expressive rationality thesis predicts that the higher people score on cognitive reflection, the more their assessments of the test's validity will turn on their prior ideological commitments, whether they lean left or right. The idea is that the ideologically motivated flatter themselves with the belief that people who share their views are more open-minded than those who do not.

So what did Kahan and his colleagues find? First of all, it turns out that conservatives and liberals score about equally badly on the cognitive reflection test: 64 percent of Republicans and 59 percent of Democrats got all three questions wrong. In fact, the difference between the two groups of partisans is less than the difference in scores associated with education, gender, and race. Recall that the Republican brain hypothesis predicted that cognitive reflection would be negatively correlated with right-wing ideology. "This hypothesis is not confirmed," concludes Kahan.

Furthermore, both liberals and conservatives displayed ideological bias when assessing the validity of the cognitive reflection test. When climate-change skeptics were characterized as open-minded, Republicans thought the test was nifty. When skeptics were branded as closed-minded, more Democrats found the test results convincing. Ideology distorts both left-wing and right-wing thinking.

Were high scorers more or less likely to be politically polarized? The researchers found that the higher either conservatives or liberals scored on cognitive reflection, the more likely they were to judge the test as valid when its results supposedly confirmed their ideological views about climate change skeptics. People skilled at systematic reasoning use that capacity to justify their beliefs rather than seek the truth.

Kahan notes that research has found political independents and libertarians score better on cognitive reflection than do liberals or conservatives. But before we brainy libertarians and independents start patting ourselves on our collective backs, could this simply mean that we are especially good at justifying our beliefs to ourselves?

The new Yale study finds that when it comes to thinking about policy-relevant scientific information that challenges their ideological views, liberals, conservatives, and, yes, libertarians are inclined to violate physicist Richard Feynman's famous "first principle." As the irreverent genius put it, "You must not fool yourself and you are the easiest person to fool." And the smarter you are, the easier it is to fool yourself.

The correct answers to the cognitive reflection test are five cents, five minutes, and 47 days.