In elections, appearance counts more than most of us care to admit. It all comes down to the brain’s orbitofrontal cortex

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Those who watched the New Hampshire Republican debate surely made a mental note of aspects of the candidates’ appearances as they staked out their turf: Ted Cruz’s jutting chin, Ben Carson’s avuncular temples, Donald Trump’s blond, blond hair, Marco Rubio’s full cheeks and boyish manner.

It’s all window-dressing, you might say; only the candidates’ positions matter. But in politics, looks count more than we care to admit.

Indeed, we often clinch our political decisions a split-second after we see a candidate and don’t change them much over time. In a 2006 study published in Psychological Science and led by Alexander Todorov of Princeton University, subjects who selected favorites after a brief glance at snapshots of unfamiliar candidates were able to predict who would win nearly 70% of the 2004 Senate and House races. When the researchers gave people more time to decide, they simply confirmed their first impressions.

In another study, published in 2008 in the Proceedings of the National Academy of Sciences, Prof. Todorov and colleague Nikolaas Oosterof digitally manipulated people’s facial features in photos, revealing just what makes us fall so hard for a candidate. They showed that a rounded, baby-faced appearance with prominent cheekbones, arched inner eyebrows and a sunny demeanor makes a person seem trustworthy.

Such snap judgments also can skew life-or-death decisions, according to a new study in Social Psychological & Personality Science. Assessments of the trustworthiness of convicted murderers based on their facial features aligned well with how they were sentenced. The sense that a prisoner was trustworthy was a good predictor of whether he got life in prison or the death sentence.

Not only do we make critical inferences about people based on their appearance, but another study, published last June in the Journal of Neuroscience, suggests that the ability to assimilate more than one piece of information about them hinges on having a healthy brain—a healthy orbitofrontal cortex, to be precise. Situated right behind the eyeballs on the floor of the skull, this area of the brain is central to social decision-making and impulse control—and to how we make political choices, according to the study.

Lesley Fellows and her team at the Montreal Neurological Institute and McGill University investigated what happens when the orbitofrontal cortex is badly damaged. How might that affect a person’s first impressions of a candidate? The researchers found seven people who had lost use of this part of their brain due to an aneurysm or tumor surgery but whose other cognitive abilities were intact. The study also included a group of 18 people with frontal lobe damage but no harm to the orbitofrontal cortex area. Another control group included matched, healthy subjects.

The researchers asked participants to look at pairs of head shots of political candidates. The subjects didn’t know the candidates and didn’t have any information about them. They first “voted” for one from each pair based on the photos. Then they rated each candidate on two traits: perceived attractiveness and competence (the latter a guess based on appearance).

The votes of the healthy participants and of the 18 people whose brain injuries did not include the orbitofrontal area included considerations of both attractiveness and competence—that is, they might vote for someone whom they judged to be competent even if that candidate wasn’t rated the most attractive. But the votes of the seven people with orbitofrontal damage matched one factor only: the candidates’ appearance. They were most likely to vote for whoever they deemed most attractive.

Even those of us fortunate enough not to have brain damage often can’t explain why we like who we like. “Eventually the brain gets overwhelmed with so many factors,” Dr. Fellows told me. “When it gets to be too much, people just simplify.”