The logic of a psychopath

Before his execution in the Florida electric chair in 1989, Ted Bundy confessed to murdering 30 young women, typically by bludgeoning them to death and often raping them as well. He almost certainly had many more victims than that, perhaps more than 100. But he avoided suspicion for much of his five-year killing spree, in part because he was good-looking and clean-cut, a college grad and a law student.

Despite this outward appearance, Bundy was socially clueless. He was introverted and by his own description had no sense of how to get along with people. Near the end of his life he described himself this way: “I didn’t know what made things tick. I didn’t know what made people want to be friends. I didn’t know what made people attractive to one another. I didn’t know what underlay social interaction.”

Psychopaths can be paradox. Some, like Bundy, are intellectually high functioning, and they clearly know right from wrong. They are not delusional, but they are socially inept. They seem to lack normal self-control, and they persistently violate social, legal and moral rules. They don’t — as Bundy’s words suggest — comprehend the human social contract.

But why? What’s the glitch in the mental machinery? Is there a specific neurological and cognitive deficit underlying their abhorrent actions? Are they incapable of weighing risk or comprehending the regular quid pro quos of social life — or both? Two psychological scientists at the University of New Mexico, Elsa Ermer and Kent Kiehl, suspected that such specific reasoning deficits might underlie the disorder, which would explain why psychopaths’ general reasoning ability seems to stay intact.

To explore these questions, Ermer and Kiehl went where they knew they’d find a good sample of psychopaths — to prison. They interviewed and tested 67 prisoners — some psychopaths and some not — for three different kinds of rule comprehension. Some of the rules were simply descriptive, for example: “If a person is from North Dakota, that person likes the cold.” Others were based on social contracts, for example: “If you borrow my car, you will have to fill the gas tank.” And finally, some of the rules were related to risk and precaution: “If you work with tuberculosis patients, you must wear a surgical mask.” They asked all the prisoners — as well as a control group of college students — to reason about these rules, to see how well they understood the different forms of reasoning.

The results were unambiguous. As reported recently in the journal Psychological Science, the prisoners who were not psychopaths reasoned pretty much like college students — that is, not great at general logic but much better at understanding social contracts and precautionary reasoning. The psychopaths also did about the same on straight logic, but they were poor at understanding social agreements and proper precautions.

Understanding quid pro quos is a core human trait, the foundation of all cooperation and morality. It’s not surprising that it would be askew in people who don’t know right from wrong, honorable behavior from cheating. It’s also not shocking that psychopaths are lousy at weighing risk and taking precautions — another core human trait. That’s why most of them get in trouble — and end up in prison.