As I professed in a previous post, I'm a hardcore believer in free will. No matter how far science goes in reducing our thoughts, emotions and decisions to deterministic physical processes, I have faith that we can, to a certain extent, choose our paths in life. And yet our freedom to choose can be compromised, undermined, subverted.

In his entertaining, disturbing new book, Split-Second Persuasion: The Ancient Art and New Science of Changing Minds (Houghton Mifflin Harcourt), Kevin Dutton, a psychologist at the University of Cambridge (where we met and became buddies in 2005), shows how easy it is for others to choose our actions for us. Indeed, Dutton—who previewed his book last year in Scientific American MIND—could have titled his book "Split-Second Manipulation".

Conformity, or groupthink—our tendency to do and even think like others—represents one of our greatest vulnerabilities. In a classic experiment carried out in the 1950s the psychologist Solomon Asch asked subjects to compare two sets of lines with each other and identify which lines were the same length. The subjects easily answered correctly when alone but not when surrounded by actors whom Asch had secretly instructed to give the wrong answer. After listening to the actors the subjects agreed with the erroneous majority opinion as often as 76 percent of the time.

Another example cited by Dutton: During the 1992 presidential race, researchers assembled two groups of students—half Republican and half Democratic—to watch a debate between the candidates Bill Clinton and George H. W. Bush. The groups contained actors who cheered Clinton and jeered Bush in one group and did the reverse in the other. After the debate the subjects were asked to rate the candidates' performances. Jeering drove down each candidate's ratings and cheering boosted them compared with a control group, regardless of the subjects' initial preference.

This is the same basic phenomenon, Dutton notes, that led television producers to add laugh tracks to their comedies decades ago. "Sometimes, it would seem, the way we see others depends on nothing more substantial than the way others see others," Dutton comments. We also defer to the trappings of authority. In famous experiments carried out by Stanley Milgram in the 1960s about one in four subjects administered what they believed to be potentially lethal shocks to strangers when ordered to do so by "technicians" wearing jeans and t-shirts. The compliance rose to 65 percent when the orders came from "professors" wearing white lab coats.

Similarly, Dutton points out, we rate people as more intelligent if we believe they are wealthy rather than poor. Expert wine-tasters insist that a vintage labeled as expensive tastes better than one labeled as cheap—even though the wines are identical. Women view men as more attractive if the men are accompanied by an attractive female. Worse, we assume that "good-looking people are good," Dutton concludes. Studies have shown that attractive defendants are more likely to be judged not guilty or, if convicted, to receive a lighter sentence than unattractive defendants.

We tend to like people with whom we think we have something in common, no matter how trivial the commonality. After reading about Rasputin, whose spell over the Russian royal family ended only with his assassination in 1916, students were more likely to view the mad monk positively if told they shared his birthday. We rate faces as more trustworthy if the images have been modified by computers to resemble us.

In addition to reviewing all this research, Dutton also interviews "persuasion grandmasters," including salesmen, political propagandists, trial lawyers, pickup artists, military interrogators and even con artists, who explain how they charm victims out of their money, possessions, secrets or disinclinations. Key factors are humor, surprise, eye contact and absolute confidence ("con," after all, is short for "confidence"). The more confident someone is, the more readily we believe him—even if he is deluded or deceptive.

Persuasion can be used for good as well as ill, of course. Psychotherapists, in a sense, try to persuade patients not to feel anxious or depressed. Dutton also describes a British policeman who excels at talking people out of committing suicide. In one case the policeman stripped off his coat to reveal a t-shirt bearing the words: "PISS OFF—I'VE GOT ENOUGH FRIENDS!" The startled would-be suicide laughed and crawled back from his window ledge.

How can we prevent ourselves from being unduly manipulated, yet keep ourselves open to legitimate persuasion? How can we keep our wills free? Dutton has persuaded me that reading his book might help.

Photo of Kevin Dutton courtesy Inkwell Photographic