Last week, David Brooks had a smart column on the essential “irrationality” of voters. (I’m defining irrationality here as any mental process that’s not rational/deliberate/System 2. I have no idea if our democracy would be better off if voters imitated the rational agents in economics textbooks. I only know that the mind doesn’t work that way.)

In reality, we voters — all of us — make emotional, intuitive decisions about who we prefer, and then come up with post-hoc rationalizations to explain the choices that were already made beneath conscious awareness. “People often act without knowing why they do what they do,” Daniel Kahneman, a Nobel Prize winner, noted in an e-mail message to me this week. “The fashion of political writing this year is to suggest that people choose their candidate by their stand on the issues, but this strikes me as highly implausible.”

Brooks goes on to cite all the usual suspects: kahnemanandtversky, Damasio, LeDoux. Aristotle might have called us the political animal, but we’re really an emotional animal, guided, for the most part, by our adaptive limbic system. At any given moment, our political beliefs emerge from the quarrel inside our head, as different brain areas are triggered by different cues. Instead of basing our votes on a careful analysis of the issues, we make political choices via emotion and intuition, which leaves us vulnerable to all sorts of biases, frames and fleeting associations.

One of the best example of this phenomenon comes from studies of voter preferences in the wake of the terrorist attacks of September 11. The psychologists Mark Landau and Sheldon Solomon took a large group of undergraduates from all across the political spectrum and had them stare at some blinking computer screens. While the blinks seemed meaningless – they lasted for just a few milliseconds, which is too fast for conscious awareness – they actually conveyed some emotionally charged information. Half of the subjects were subconsciously “primed” with stimuli that evoked the terrorist attacks, like the letters WTC or the numbers 9/11. The rest of the subjects just looked at area codes and random groupings of letters.

After the priming session, the scientists asked the subjects a series of political questions. For instance, after reading a series of sentences that strongly supported President Bush and his policies – “I appreciate our President’s wisdom regarding the need to remove Saddam Hussein from power,” etc. – they were asked to rate, on a scale of 1 to 5, whether or not they agreed with the paragraph.

The results were dramatic. When people were primed with neutral stimuli, they gave the sentences an average rating of 2.1, which meant they were in mild disagreement. In general, they thought Bush’s post-9/11 policies were a mistake. However, when the subjects were subconsciously exposed to words and numbers that reminded them of terrorism, their political opinions were reversed. They now gave the sentences a rating of 3.75, signaling a rather strong endorsement of the Bush administration.

Landau and Solomon then looked at how the threat of terrorism affected the 2004 Presidential election. One group of subjects was asked to think about the possibility of their own death, a process Landau and Solomon refer to as “mortality salience”. (Landau and Solomon had previously shown that reminders of 9/11 made people much more likely to think about death and dying.) The other group was primed with thoughts of pain, so that they ended up contemplating their most painful personal experiences. The subjects then completed a short survey about either President Bush or John Kerry, in which they were asked to rate both candidates on a nine-point scale.

When people were asked to think about pain, they preferred Kerry by a wide margin. His average rating was 5.5 points, compared to Bush’s 2.2. However, when the scientists triggered thoughts of death – the mortality salience condition – Bush suddenly became much more popular. In fact, he was now given significantly higher ratings than Kerry, even though a plurality of the participants described themselves as liberal.

While the scientists associate such a conservative tilt with “terror induced irrationality,” it’s not clear that these people are any more irrational than those who chose Kerry after being primed with “pain”. In both instances, different emotional cues trigger a slightly different set of emotional brain areas, which end up shaping our preferences.

My favorite study of voter irrationality is this one, which looked at voting patterns from the 2000 election in Arizona. After analyzing the data, and controlling for every conceivable variable, the researchers concluded that our decisions in the ballot box are significantly altered by our surroundings. For example, voters were nearly three percent more likely to support an increase in the state sales tax if they voted in a school. They were also significantly more likely to oppose a stem cell initiative if they had recently seen a church. According to the researchers, such “contextual biases” are potent enough to affect even a moderately close election.