idioms for self-control invoke the concept of force, such as willpower, force of will, strength of will, and self-restraint. The linguist Len Talmy has noticed that the language of self-control borrows from the language of force dynamics, as if self-control were a homunculus that physically impinged on a stubborn antagonist inside the skull.111 We use the same construction in Sally forced the door to open and Sally forced herself to go to work; in Biff controlled his dog and Biff controlled his temper. Like many conceptual metaphors, SELF-CONTROL IS PHYSICAL EFFORT turns out to have a kernel of neurobiological reality.
In a remarkable set of experiments, Baumeister and his collaborators have shown that self-control, like a muscle, can become fatigued. Their laboratory procedure is best introduced by quoting from the Method section of one of their papers:Procedure. Participants signed up for a study on taste perception. Each participant was contacted to schedule an individual session, and at that time the experimenter requested the participant to skip one meal before the experiment and make sure not to have eaten anything for at least 3 hr.
The laboratory room was carefully set up before participants in the food conditions arrived. Chocolate chip cookies were baked in the room in a small oven, and, as a result, the laboratory was filled with the delicious aroma of fresh chocolate and baking. Two foods were displayed on the table at which the participant was seated. One display consisted of a stack of chocolate chip cookies augmented by some chocolate candies. The other consisted of a bowl of red and white radishes.112
The cover story was that the experiment was on sensory memory and that the participants would experience one of two distinctive tastes and have to recall its qualities after a delay. The experimenter told half the participants to eat two or three of the cookies, and the other half to eat two or three of the radishes. She left the room and watched through a one-way mirror to confirm that the participant did not cheat. The article notes: “Several of them did indicate clear interest in the chocolates, to the point of looking longingly at the chocolate display and in a few cases even picking up the cookies to sniff at them.” The experimenter then told them they would have to wait fifteen minutes for the test of their memory of the taste. In the interim, they were to solve some puzzles that required tracing a geometric figure with a pencil without either retracing a line or lifting the pencil off the paper. Compounding the sadism, the experimenters had given them puzzles that were unsolvable, and measured how long the participant persisted before giving up. The ones who had eaten the cookies spent 18.9 minutes and made 34.3 attempts to solve the puzzle. The ones who had eaten the radishes spent 8.4 minutes and made 19.4 attempts. Presumably the radish eaters had depleted so much of their mental strength in resisting the cookies that they had little left to persist in solving the puzzles. Baumeister called the effect ego depletion , using Freud’s sense of ego as the mental entity that controls the passions.
The study raises many objections: maybe the radish eaters were just frustrated, or angry, or in a bad mood, or hungry. But the Baumeister team addressed them and over the following decade accumulated a raft of experiments showing that just about any task that requires an exercise of willpower can impede performance in any other task that requires willpower. Here are a few tasks that can deplete the ego:• Name the color in which a word is displayed (such as the word RED printed in blue ink), ignoring the color it spells out (the Stroop task).
• Track moving boxes on a screen, as if playing a shell game, while ignoring a comedy video on an adjacent screen.
• Write a convincing speech on why tuition fees should be raised.
• Write an essay about the typical day in the life of a fat person without using any stereotypes.
• Watch the scene in Terms of Endearment in which a dying Debra Winger says good-bye to her children, without showing emotion.
• For racially prejudiced people, carry on a conversation with an African American.
• Write down all your thoughts, but don’t think of a polar bear. 113
And here are some of the lapses in willpower that result:• Giving up sooner when squeezing a handgrip, solving anagrams, or watching a movie of a box on a table until something happens.
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