Are the endless decisions of modern life leading to decision fatigue，depleting（耗尽）our willpower（意志力）to the point that we end up making increasingly poor，even self-destructive choices?
In an excerpt adapted from his book,John Tierney makes the case that they do.The piece opens with a description of research on parole（假释）decisions made by Israeli judges，which found that the judges were dramatically more likely to free prisoners earlier in the day or right after lunch,compared with other times.
But Stanford psychology professor Carol Dweck has found an interesting perspective.Her research shows that while decision fatigue does occur,it primarily affects those who believe that willpower runs out quickly.
"We find that people get fatigued or depleted after a difficult task only when they believe that willpower is a limited resource,but not when they believe it's not so limited,"says Dweck.Because the majority of people tend to view their stores of willpower as being limited,the effect appears universal in studies that don't distinguish between people holding various beliefs.
"If you look over our studies,we get effects that look like overall fatigue.But when you break it down into the people who believe willpower is limited and those who donI',you have two separate groups," says Dweck. "In fact, in some cases,the people who believe that willpower is not so limited actually perform better after a difficult task."
In the excerpt,Tierney cites research showing that consumption of sugar restores depleted willpower.One study involved giving people either thick,tasty milkshakes or flavorless,low-fat drinks after a series of decision-based tasks had reduced their performance. As long as the food contained sugar, it didn't matter whether the stuff was rewardingly tasty. Although the researchers initially thought that indulging in something pleasurable would reduce participants' decision fatigue, it turned out that it was the sugar,not the pleasure,that actually boosted brain performance.
Other studies have shown that,similarly,sugar consumption reduces people's expressions of prejudice,presumably by helping them maintain self-restraint.
Dweck has tested how this idea fits with her theory on willpower:“We find that sugar improves self-control only for the people who believe in limited willpower,"she says."We think that people who believe in limited willpower are always checking to see how fatigued they are.If they feel fatigued,they show a deficit.If you give them sugar and they get a surge of energy,they don't show a deficit.”
What effect does sugar have on those believing in limited willpower according to Dweck?