Belief in Limited Willpower Is Self-fulfilling?

(see previous discussion of ego-depletion)

It looks like people studying people’s decline in vigilance-required tasks over time need to take care not to suggest to their subjects the idea that they will probably fatigue.  The theory is that tasks that specifically require “self control” can lead to specific fatigue in other “self control” tasks, as distinct from general mental fatigue, although it’s been found that glucose availability to the brain explains most of this.

A new study, which is much more careful than past ones, gives a pretty strong idea that people’s expectations for how they’ll perform while willpower-taxed are the determining factor (at least for artifical, low-motivation psych-study tasks), and further that when these expectations are manipulated (by push polling), that this obliterates the effects typically reported in the ego-depletion literature. Because of the push polling affecting performance, you can’t just say that it’s ’the person’s idiosyncratic “availability of willpower” after a demanding task that shapes idiosyncratic beliefs about willpower’.

I reproduce here my comments from this LessWrong discussion:

What’s demonstrated: if you prime an excuse for doing poorly, you will do poorly. I think there’s already some similar research (different types of excuses, though). They also show that self-reported exhaustion (not just “ego depleting” tasks) leads to a difference in performance that goes in exactly the direction that the subjects are primed to believe (either being reminded of an existing belief, or being tricked into holding it with biased questions).

It surprises me that, of the people who don’t claim to expect to flag when fatigued, those who report being exhausted by the depletion task actually make less errors than those who don’t. Unless this is just due to warming up their inhibition/vigilance (both the initial and final tests require it) while, it suggests that positive expectations can boost performance, not just that available excuses can harm it.

I like that they demonstrated that errors on IQ problems tracks errors on mundane rule-following, vigilance type tasks, but it’s amusing to me that people who believe they’ll do worse when fatigued, actually test as smarter (less IQ test errors) when fresh, whereas those primed to believe they won’t effectively fatigue improve slightly, but are still worse than the “limited resource” believers initial performance. This effect is still there, but probably not significant, for the simple but tiresome “willpower” testing (Stroop) task. I assume the “limited”-believers are more engaged by an IQ-proving question, either for signaling or entertainment, compared to the boring Stroop task. Disclaimer: these differences, from figures in pg 5 of the 

paper. aren’t strongly significant (N ~= 50), so maybe I shouldn’t conclude anything (the authors don’t pin anything on them).
It seems reasonable to me that push polling about someone’s future behavior will lead them to act consistently with the signal they just sent in the poll - like in Cialdini’s Influence, where people are polled on whether they like to go to opera, or give charitably, by some attractive person they want to impress, and then after affirming are ambushed with a sales pitch (they thought it was an innocent poll but are trapped by their answers). So it seems reasonable to assume that those who were push-polled into believing they will become either sloppier, or more accurate, with fatigue, would act consonantly.

But I don’t think this objection is likely the whole story. The simplest explanation is that people’s stated expectations of their performance do shape their performance - the power of positive thinking, and obviously, negative. (possibly unvoiced/persistent expectations as well as explicitly declared, although of course it’s nearly impossible to measure such things surreptitiously).