Stanford Report has a university public press release about a recent paper [subscription required] in Psychological Science. The paper is available for free from a website of one of the authors.
The gist is that they find evidence against the (currently fashionable) hypothesis that willpower is an expendable resource. Here is the leader:
Veronika Job, Carol S. Dweck, and Gregory M. Walton
Stanford University
Abstract:Much recent research suggests that willpower—the capacity to exert self-control—is a limited resource that is depleted after exertion. We propose that whether depletion takes place or not depends on a person’s belief about whether willpower is a limited resource. Study 1 found that individual differences in lay theories about willpower moderate ego-depletion effects: People who viewed the capacity for self-control as not limited did not show diminished self-control after a depleting experience. Study 2 replicated the effect, manipulating lay theories about willpower. Study 3 addressed questions about the mechanism underlying the effect. Study 4, a longitudinal field study, found that theories about willpower predict change in eating behavior, procrastination, and self-regulated goal striving in depleting circumstances. Taken together, the findings suggest that reduced self-control after a depleting task or during demanding periods may reflect people’s beliefs about the availability of willpower rather than true resource depletion.
(HT: Brashman, as posted on HackerNews.)
As a personal anecdote, I have never felt anything that I was inclined to call "willpower depletion". As a teenager, I decided that "willpower" was just a loaded term/metaphor for dynamic consistency, and that calling it "willpower" was harmful to the way people thought about themselves as agents. I decided that other people's feeling of "willpower depletion" was nothing more than sensing oneself in transition from one value system to another.
But claims that the theorized "executive system", a cognitive system whose function is almost by definition to maintain dynamic consistency, was seated in the prefrontal cortex and needed more glucose than other brain functions, made me consider that maybe "willpower" is in fact an appropriate term... but I still never actually felt anything like a "depleting resource", which I found confusing.
So I'll be less confused again if the belief dependency you mention is correct, and causal. In any case, I hope it is, so that people can achieve better dynamic consistency by not thinking of it as "expendable". I'm at least one example consistent with that theory.
With respect, I've always found the dynamic inconsistency explanation silly. Such an analysis feels like one is forcing, in the face of contradictory evidence, to model human beings as rational agents. In other words, you look at a person's behavior, realize that it doesn't follow a time-invariant utility function, and say "Aha! Their utility function just varies with time, in a manner leading to a temporal conflict of interests!" But given sufficient flexibility in utility function, you can model any behavior as that of a utility-maximizing ... (read more)