The Busy and Depleted System 2

THE BUSY AND DEPLETED SYSTEM 2

Kahneman treats both self-control and cognitive effort as forms of mental work. He describes studies in which people facing a demanding cognitive task and a temptation at the same time were more likely to yield to the temptation. Imagine that you are asked to retain a list of seven digits for a minute or two. You are told that remembering the digits is your top priority. While your attention is focused on the digits, you are offered a choice between two desserts: a sinful chocolate cake and a virtuous fruit salad. The evidence suggests that you would be more likely to select the tempting chocolate cake when your mind is loaded with digits. System 1 has more influence on behavior when System 2 is busy, and it has a sweet tooth.

The studies discussed here also linked being cognitively busy with selfish choices, sexist language, and superficial judgments in social situations. Memorizing and repeating digits loosens the hold of System 2 on behavior, but of course cognitive load is not the only cause of weakened self-control. A few drinks have the same effect, as does a sleepless night. The self-control of morning people is impaired at night; the reverse is true of night people. Too much concern about how well one is doing in a task sometimes disrupts performance by loading short-term memory with pointless anxious thoughts. The conclusion is straightforward: self-control requires attention and effort. Another way of saying this is that controlling thoughts and behaviors is one of the tasks that System 2 performs.

Roy Baumeister and his colleagues investigated a different proposal: that cognitive, emotional, and physical effort draw partly on a shared resource. Their experiments used successive rather than simultaneous tasks. This was a proposed explanation of the results, rather than a conclusively established pool of mental energy.

Baumeister’s group reported that exerting will or self-control on an initial task was followed by reduced willingness or ability to persist on another task. The phenomenon has been named ego depletion. In a reported demonstration, participants instructed to stifle their emotional reaction to an emotionally charged film later performed less well on a test of physical stamina—how long they can maintain a strong grip on a dynamometer in spite of increasing discomfort. The researchers interpreted the shorter persistence as an effect of the earlier emotional effort. In another experiment, participants ate radishes and celery while resisting chocolate and rich cookies. They subsequently gave up earlier on a difficult cognitive task, a result the researchers also interpreted as depletion.

Tasks studied as possible causes of ego depletion involved conflict or suppressing a natural response. They included:

• avoiding the thought of white bears
• inhibiting the emotional response to a stirring film
• making a series of choices that involve conflict
• trying to impress others
• responding kindly to a partner’s bad behavior
• interacting with a person of a different race (for prejudiced individuals)

Outcomes interpreted as signs of depletion included:

• deviating from one’s diet
• overspending on impulsive purchases
• reacting aggressively to provocation
• persisting less time in a handgrip task
• performing poorly in cognitive tasks and logical decision making

In this account, activities that impose high demands on System 2 require self-control, and exerting it can be unpleasant. The proposed ego-depletion effect differs from cognitive load because it may partly involve motivation. After exerting self-control in one task, you do not feel like making an effort in another, although you could do it if you really had to. In several experiments, people were able to resist the effects of ego depletion when given a strong incentive to do so. In contrast, increasing effort is not an option when you must keep six digits in short-term memory while performing a task. Ego depletion is not the same mental state as cognitive busyness.

Baumeister’s group also proposed glucose as a mechanism. The brain uses glucose, but that fact alone does not show that a demanding task exhausts a supply of willpower or that sugar restores it. Kahneman describes experiments that the researchers interpreted as supporting this hypothesis.

Volunteers in one of their studies watched a short silent film of a woman being interviewed and were asked to interpret her body language. While they were performing the task, a series of words crossed the screen in slow succession. The participants were specifically instructed to ignore the words, and if they found their attention drawn away they had to refocus their concentration on the woman’s behavior. The researchers used this task to induce what they interpreted as ego depletion. All the volunteers drank some lemonade before participating in a second task. The lemonade was sweetened with glucose for half of them and with Splenda for the others. Then all participants were given a task in which they needed to overcome an intuitive response to get the correct answer. The Splenda group showed the performance decline the researchers expected, while the glucose group did not. The result was interpreted as support for the glucose hypothesis. It does not by itself establish the proposed brain-energy mechanism or a reliable remedy for lapses of self-control.

A study discussed in the Proceedings of the National Academy of Sciences examined decisions by eight parole judges in Israel. They reviewed applications throughout the day, spending an average of 6 minutes on each case. Overall, only 35% of requests were approved. The researchers recorded decision times and the judges’ morning, lunch, and afternoon food breaks. Approval rates were about 65% after breaks and fell toward zero before the next break, roughly two hours later. The authors considered alternative explanations and attributed the pattern to fatigue and hunger. But an observational association with break timing does not by itself isolate those causes from case order, scheduling, or other differences across sessions.