No Sugar Coating Problems for the Glucose Model
So, I got a unique invitation from Edge.org creator John Brockman back in September of last year. He was organizing an event which he dubbed HeadCon. He invited a group of scholars to give brief talks on the topic of our choice, to be recorded close up. The camera coming in tight on people’s heads was the origin of the “Head” part of HeadCon.
Our marching orders were to talk about what was new in our respective areas of social science and why whatever was new mattered, eschewing our “canned” presentation, keeping our remarks “conversational.” The talks, along with a pretty creepy video of a face, can be found on the HeadCon web page.
I used the opportunity to talk about a topic that I’ve been oddly obsessed with over the last few years, the idea that “willpower” is fueled by a mysterious resource, and the subsidiary idea that glucose is the mysterious resource in question. (I’ve discussed these ideas in prior blog posts. I and some of my colleagues at Penn have also recently provided an alternative account, for those interested. Another account just came out in Trends in Cognitive Science.)
To get at this (narrow) topic I framed my remarks in the (broad) context of the current discussion in psychology about replication. (Indeed, the title on the web site of my talk is P-hacking and the Replication Crisis.) More or less, the theme I tried to hit – and now you don’t have to sit through the video of my presentation – is that there’s just a ton of reasons to think that the “resource model” of self-control is wrong and yet the model… Just. Won’t. Die.
At HeadCon, I told the story of my experiences with the willpower-as-resource model, which I quote here a bit, despite how unseemly it is to quote oneself.
… I started just talking informally with colleagues about this. I would go to give talks in places and, lo and behold, it turns out there’s this kind of background radiation—there’s the dark matter of psychology – which is a few people who fail to replicate and don’t publish their work and also don’t talk about it … It’s sort of like sex, it’s the thing that we’re all doing, we’re all replicating, we just don’t want to talk about it too much, right?…Once I did that I started getting the sense that I was fishing into literature where there’s no there there. … more and more work is coming out that’s very difficult to interpret under the willpower model.
I’m pleased to report that after discussing my frustration with the fact that the resource model refused to die its appropriate death, the good people at Edge chose to run with my suggestion that this could be a good Edge Question. To wit, the 2014 question was: “What scientific idea is ready for retirement?” The Times just ran a little piece on it.) (And, I admit, I basically just cribbed from my talk for my own answer. Sue me.)
In any case, it’s in this context that I thought I would discuss, briefly, a new paper out in Appetite. The (provocative) title is, Sweet Delusion: Glucose Drinks Fail to Counteract Ego Depletion, and the authors – Florian Lange and Frank Eggert – report two experiments (N = 70, N = 115) in which they tried to replicate the results of two studies (Gailliot et al., 2007; Hagger et al., 2010) purporting to show that drinking a sugary beverage improves subsequent performance on a “self-control” task. The idea is that glucose is the fuel for self-control, so drinking a sugary drink will improve performance on a task the requires self-control.
Lange and Eggert begin their paper by pointing out a number of reasons to doubt the glucose-as-resource as model, including referring to the recent paper by Schimmack, which discussed some statistical worries about one of the key papers in this literature, the 2007 paper by Gailliot et al. in the Journal of Personality and Social Psychology. Lange and Eggert add a number of other worries regarding these findings, including pointing to some errors in a recent meta-analysis by Hagger et al., (2010), writing:
In sum, the original (Gailliot et al., 2007) and meta-analytic (Hagger et al., 2010) evidence is less compelling than suggested, illustrating that the effect of sugar supplementation on ego depletion is far from being an established research phenomenon.
In the first study, subjects drank either a regular sugary beverage or a sugar-free version, and were subsequently given a task that measured discounting, willingness to forgo a smaller, sooner payoff in favor of a larger, later one, with choosing the latter sorts of payoffs considered to indicate a greater ability to exert “self-control.” They found no effect of condition, despite their calculation that “an effect of glucose consumption on ego depletion as large as reported by Hagger et al. (2010) or Wang and Dvorak (2010) could have been detected with a probability close to 1 (1-β > .99).” A second experiment, in which subjects merely rinsed with the glucose solution, instead of drinking it, yielded a similar null result. The authors conclude:
In line with an increasing body of evidence demonstrating that (a) exerting self-control is unlikely to reduce blood glucose levels (Kurzban, 2010; Molden et al., 2012), and (b) performance on a second self-control task does not vary as a function of participants’ blood glucose levels (Dvorak & Simons, 2009; Schimmack, 2012), the present results question the validity of the glucose model of self-control. Especially in view of the above-mentioned shortcomings of studies supporting the role of blood glucose in ego depletion, the model’s major strength appears to lie in its ostensible support for “the folk notion of willpower” (Gailliot & Baumeister, 2007, p. 304) and not in its empirical corroboration… These findings require models positing a major role for glucose in self-control to be fundamentally revised if not completely abandoned.
I was recently surprised to get a phone call from someone involved with organizing the 2014 American Psychological Society (APS) convention in San Francisco in May. The idea was to have a public debate between me and Roy Baumeister about the depletion model of self-control. I agreed to participate in the debate, but was recently informed that the other party declined the opportunity to participate. So, I’ll just present my own thoughts during a session at APS this year. Should be fun.
References
Dvorak, R. D., & Simons, J. S. (2009). Moderation of resource depletion in the self control strength model: Differing effects of two modes of self-control. Personality and Social Psychology Bulletin, 35(5), 572-583.
Gailliot, M. T., Baumeister, R. F., DeWall, C. N., Maner, J. K., Plant, E. A., Tice, D. M., Brewer, L.E., & Schmeichel, B. J. (2007). Self-control relies on glucose as a limited energy source: willpower is more than a metaphor. Journal of personality and social psychology, 92(2), 325.
Hagger, M. S., Wood, C., Stiff, C., & Chatzisarantis, N. L. D. (2010). Ego depletion and the strength model of self-control: A meta-analysis. Psychological Bulletin, 136(4), 495-525.
Kurzban, R., Duckworth, A., Kable, J. W., & Myers, J. (2013). An opportunity cost model of subjective effort and task performance. Behavioral and Brain Sciences, 36(06), 661-679.
Lange, F. & Eggert, F. (2014). Sweet delusion: Glucose drinks fail to counteract ego depletion. Appetite.
Molden, D. C., Hui, C. M., Noreen, E. E., Meier, B. P., Scholer, A. A., D’Agostino, P. R., &
Martin, V. (2012). The motivational versus metabolic effects of carbohydrates on selfcontrol. Psychological Science, 23, 1130–1137.
Wang, X. T., & Dvorak, R. D. (2010). Sweet future: Fluctuating blood glucose levels affect future discounting. Psychological Science, 21(2), 183-188.
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