The Reins of Self-Control

A charioteer stands astride a chariot, pulled by a pair of winged horses in a great arc across the heavens. One steed is noble and obedient, the other impulsive and unruly, and it falls upon the charioteer to control the reins.

This image from Plato’s Phaedrus is a description of the self, struggling to control impulses and overcome desires. Throughout history, humans have tried to explain how we control our actions – now modern psychology is taking its turn. A recent study, published in the September issue of the journal Psychological Science, suggests that how we perceive our self-control and willpower may have a dramatic influence over how we use it.

“It’s in your head; what you think about willpower is what really matters,” said University of Zurich psychologist Veronika Job, lead author of the study.

In Job’s experiment, participants first rated how much they agreed with statements like: “After a strenuous mental activity your energy is depleted and you must rest to get it refueled again.” These surveys were meant to assess their views about self-control. Next, they completed several tasks requiring self-control, like following complex instructions about how many letter e’s to cross out on a page, and identifying the names of colors in which the hue and meaning did not always match (for example, the word “green” would sometimes appear in red).

In the next round of tests, a different set of participants did exactly the same thing, except their initial questionnaires were biased in one of two ways – either by heavily suggesting that strenuous tasks use up willpower or that those same tasks are actually quite energizing.

Job found that people performed worse if they had the expectation (or by suggestion were led to think) that their willpower was a limited resource. People who thought they “used up” their self-control on the first task performed poorly on the second. On the other hand, people who already thought, or were led to believe, that the first task was “energizing,” performed just as well on the second.

To Job and other psychologists, these results have implications for vulnerable populations, including people struggling to avoid unhealthy habits (like overeating) or people in demanding situations (like final exams). Many behavioral and social problems – such as drug abuse, crime, unwanted pregnancy, overspending, or school underperformance – stem from failures in self-control. If changing people’s theories about willpower can actually change their impulsive behavior, we may have more control over the reins than we thought, according to psychologist Rob Dvorak from the University of South Dakota.

Still, the notion of self-control is complex, and expectation may be just one of many interacting elements. “Expectancies are usually based on real phenomena,” said psychologist Roy Baumeister of Florida State University, “so this is likely to be part of, not all of, the story.”

Baumeister and his colleagues were the first to propose what has been the prominent theory of self-control for the last ten years: the strength model. It asserts that self-control is a finite resource depleted with use, and has explained people’s performances on a wide range of activities, from suppressing emotions to resisting tempting food.

“[The theory says] self-control is like a tank we have, and some people have tanks of different sizes,” said Martin Hagger, a psychologist at the University of Nottingham in the U.K. What began as a metaphor has taken a literal turn in the past few years, with other researchers investigating a possible biological fuel for the tank: blood glucose. Brain activity requires glucose, and some studies report a small decrease in blood glucose after acts of self-control. But the glucose evidence hasn’t convinced everyone.

“You’re not going to run out of glucose if you do a math problem,” said Hagger. In fact, the amount of glucose used by the brain in these mathematical tasks is minimal – less than a tenth of a Tic-Tac. Instead, as the Job study suggests, self-control might depend more on people’s expectations, which can be altered by mere suggestion.

“Changing what people expect to happen can change what happens,” said Dvorak.