I felt that Robert Kurzban presented a pretty good argument against the "willpower as a resource" model in Why Everyone (Else) Is a Hypocrite:
[After criticizing studies trying to show that willpower is a resource that depends on glucose]
What about the more general notion that “willpower” is a “resource” that gets consumed or expended when one exerts self-control? First and foremost, let’s keep in mind that the idea is inconsistent with the most basic facts about how the mind works. The mind is an information-processing device. It’s not a hydraulic machine that runs out of water pressure or something like that. Of course it is a physical object, and of course it needs energy to operate. But mechanics is the wrong way to understand, or explain, its action, because changes in complex behavior are due to changes in information processing. The “willpower as resource” view abandons these intellectual gains of the cognitive revolution, and has no place in modern psychology. That leaves the question, of course, about what is going on in these studies.
Let’s back up for a moment and think about what the function of self-control might be. Taking the SATs, keeping your attention focused, and not eating cookies all feel more or less unpleasant, but it’s not like spraining your ankle or running a marathon, where the unpleasant sensations are easy to understand from a functional point of view. The feelings of discomfort are probably the output of modules designed to compute costs. When your ankle is sprained, putting weight on it is costly because you can damage it further. When you have been running for a long time, the chance of a major injury goes up. These sensations, then, are probably evolution’s way of getting you to keep your weight off the joint and stop doing all that running, respectively.
There’s nothing obviously analogous for not eating cookies or doing word problems. Why does it feel like something, anything at all, to (not) do these things? As we’ve seen, lots of other stuff happens in your head, all the time, and it doesn’t feel like anything. Further, given that it seems as if exerting self-control is a good thing, that is, that it generally leads to outcomes that might be expected to yield fitness benefits, you might expect that exerting self-control would feel good and easy. Why does it seem hard, and feel even harder over time? What is the sensation of “effort” designed to get you to do?
One reason it seems hard might derive from that fact that “exerting self-control” entails incurring immediate costs in various forms, and “effort” is the representation of these costs. Consider not eating a cookie. There are probably modules in your mind that are designed to compute the benefits of eating nice calorie packages. They’re wired up to the senses, designed to calculate just how good (in the evolutionary sense) eating the calorie package is. From the point of view of these modules, not eating the cookie is a cost, in particular, the lost calories in the cookie. So, the sensation of the effort of not eating it—”temptation”—is probably evolution’s way of getting you to eat the cookie, just as the sensation of pain is evolution’s way of getting you to stay off your sprained ankle. In both cases, the experience is the output of a module designed to compute costs.
The same argument applies to other opportunities, and they take various forms. In some experiments, subjects are told to ignore words flashing on a computer screen, something that feels quite effortful. Why? Well, not reading words on a screen carries a loss of information: What did those words say? A similar argument applies regarding Ariely’s work on decision making during sexual arousal, which we looked at earlier in this chapter. The reason that subjects respond to those survey questions when they are aroused is probably because the mechanisms designed to take advantage of mating opportunities are computing benefits in the environment, though they are being fooled by the fact that the images they are getting are pictures rather than actual people.
Is it also a cost to solve word problems? Sure, but the cost isn’t caloric. Solving word problems requires the use of certain fancy modules, and when one is doing one of these tasks, these modules are kept busy. This means that doing these tasks carries real (opportunity) costs: all the things that these modules could be doing but are not because they are engaged. It’s not unlike what happens when you start up some big piece of software on your computer: Other things suffer, necessarily. Starting up software carries these costs. Working on word problems, similarly, prevents you from using important modular systems from doing other tasks.
So, instead of a resource view, my view is that the issue is more of an effort monitor—an “effortometer”62 in the mind. My guess is that the reason it feels like something to pay close attention to something, solve hard problems, or avoid eating cookies is that doing these things is costly from the perspective of certain modules.63 The feeling of “mental effort,” on this view, is like a counter, adding up all these opportunity costs to determine if it’s worth continuing to do whatever one is doing.64 As these costs get higher—either because one is doing the task for a while, or for some other reason—the effortometer counts higher, giving rise to the sensation of effort, and also giving the impatient modules more and more of an edge.
If I’m working on word problems—but not getting anywhere—using my modules in this way isn’t doing much good, so maybe I should stop. Interestingly, as illustrated by the results of the studies described above, the effect seems to extend from one task to another, even if the tasks are quite different.
This idea suggests that a mechanism is needed that performs these computations, weighing the costs and benefits of doing tasks that make use of certain modules. Some modules are counting up these costs, and when the effortometer increases, there is less suppression of the short-term modules—it’s time to move on. So, it’s not “willpower” that’s exhausted—it’s that the ratio of costs to reward is too high to justify continuing. As Baumeister himself indicated, “it is adaptive to give up early on unsolvable problems. Persistence is, after all, only adaptive and productive when it leads to eventual success.”
The effortometer view suggests a way to “reset” or at least reduce the count. Suppose we give subjects a reward, such as a small gift, or even light praise; this ought to “reset” the counter, just as when a foraging animal’s time is rewarded by finding food morsels. Diane Tice and colleagues conducted some work in which some subjects were told not to think of a white bear,* and others were not. The idea was that not thinking of a white bear takes some “willpower,” and when you’ve just used your willpower, you have less of it left to use in the next task, which was drinking an unpleasant beverage. They found that if you have to suppress thinking of a white bear, you can’t drink as much of the awful Kool-Aid. So, that looks good for a “resource” model. Your willpower sponge has been squeezed out.
Some subjects were, however, given a small gift after suppressing thinking of a white bear. These subjects were able to drink just as much of the nasty stuff as those who were at liberty to think of as many white bears as they wanted. That is, their “willpower” seems to have been restored, making them able to endure the foul-tasting beverage.
These findings are very hard to accommodate with a “resource” model. If my self-control sponge is squeezed dry by not thinking of a white bear, a gift shouldn’t help me exert willpower—I’m all out of it. (And certainly the gift didn’t increase the amount of glucose in my body.) In contrast, this finding fits very well with the effortometer model. If the effortometer is monitoring reward, then a gift resets it, and ought to improve subsequent self-control tasks.
Elsewhere in the book (I forget where) he also notes that the easiest explanation for people to go low on willpower when hungry is simply that a situation where your body urgently needs food is a situation where your brain considers everything that’s not directly related to acquiring food to have a very high opportunity cost. It seems like a more elegant and realistic explanation than saying the common folk-psychological explanation that seems to suggest something like willpower being a resource that you lose when you’re hungry or tired. It’s more of a question of the evolutionary tradeoffs being different when you’re hungry or tired, which leads to different cognitive costs.