Theories of willpower
I have been thinking quite a lot recently about “mental efforts”. The project I am currently working on requires me to sit in a tiny room and stare at a computer screen for hours on end. It has been lots of fun but also very challenging mentally, mainly because I do not have a clear list of actionable tasks to work through and have to decide on the next steps as I go along. I have noticed that my willingness to start something new or focus hard varies immensely during the day. In the morning, I usually have no problem trying out new things and coding intensely for prolonged amounts of time. However, as the day wears on, this zealousness disappears and I tend to drift off or find myself unwilling to implement a new idea. When the situation gets too dire, going for a walk or the gym usually helps me regain some mental energy and I can return to work somewhat restored. This whole experience has made me wonder what it really means to expend mental effort and why some things are harder than others. It sounds ludicrous, but for me, it is not really clear, why my brain has no issue reading fiction for hours but is left fatigued by even an hour of studying something I dislike. How come I just went home because I could not force myself to work anymore but writing this essay is fine?
There are various approaches to describe what willpower is and why we never seem to have enough of it (see here for another introduction to the topic). In this post, I will go over prominent theories and evaluate which seem the most plausible to me.
I The Glucose theory
Some of the most renowned theories model willpower as a finite resource. It is depletable and the more you use it now the less you have for later. There are several different approaches, some of which hypothesize this resource to be an abstract concept like motivation, others propose an actual physical substance. This substance is most often made out to be glucose.
Matthew Gailliot and Roy Baumeister, both social psychologists, conducted several experiments supporting the theory [1]. In the first one, the participants watched a video of a woman speaking while words appeared in the bottom corner of the screen. Part of the audience was asked to focus on the woman’s face and ignore the text while the controls were told to watch the video as they normally would. Physiological measurements showed that the active group’s blood glucose was reduced afterwards while no such effect was observed in the controls. In another experiment, the researchers investigated whether a low level of blood glucose was predictive of poor performance in the Stroop test, a measure of self-control. Words indicating colours (i.e. red, green blue) were printed on a screen in a different colour (i.e. red, green, blue). The subjects had to name the ink colour and therefore expend mental effort to override the urge to simply read the word aloud. Beforehand, the participants had watched the same video as in experiment 1. The blood measurements showed that “lower glucose after having watched the video was associated with poorer Stroop performance”, a result that remained significant even after controlling for baseline glucose levels. In a third experiment, the participants were split into an active and a control group and had to watch the video of the woman and the words again. Afterwards, they were given a drink that either contained sugar or a sweet placebo and then completed the Stroop test again. The analysis showed that among the sugar drinkers, both groups (focused and casual watchers) made the same amount of errors, however, in the placebo group the focused group more mistakes. Baumeister conducted further experiments to replicate these findings, however, these three demonstrate his core statement.
Since its publication, this theory has come under criticism. In “Does the Brain Consume Additional Glucose During Self-Control Tasks?” Rob Kurzban criticizes the underlying model proposed by Baumeister [2]. He casts into doubt the assumption that strenuous mental activity has a meaningful influence on the glucose levels in the blood by calculating the additional energy consumption in the brain. Several studies he cites have come to the conclusion that exercising self-control changes the glucose expenditure very little, if at all (see [3], [4], [5], [6]). Instead, Kurzban proposes that glucose affects performance by acting as an input (and not as a resource) to the brain. Reduced occurrence in the bloodstream might signal that the body is running low on calories and that mental resources should be allocated to procuring food. His findings are supported by Chambers, Bridge, and Jones [7] who ran a study telling participants to take a glucose-rich beverage into their mouths and spit it out afterwards, which resulted in an improvement in their physical performance. If this translates into mental performance, Baumeister’s position could be undermined. The resource theory takes further hits from a meta-analysis that found signs of publication bias and called the results of the studies “too good to be true” [8].
Are you confused yet? If not, Job et al. tried to test whether beliefs about whether willpower is limited affected the influence of sugar consumption on the Stroop test [9]. And it did! Participants who believed willpower is not a finite resource showed no improvements from ingesting glucose while non-believers did. This is getting murkier than the water collected in my pots after a week of not doing dishes, so I’m moving on to the next theory in line.
II The cost/benefit theory
Kurzban, one of the chief critics of the model mentioned above has proposed his own theory: he posits that mental effort is the felt output of doing cost/benefit analyses in order to decide which task has the highest expected utility [10]. The brain cannot do everything at once and has to prioritize. Should I play a game or clean my room instead? While executing a task, the brain constantly compares the gained utility with the utility it expects to gain from choosing the next best option. Kurzban gives the example of a study participant who is told to solve a difficult math problem. There are long-term advantages of working on the task (improved math skills) and short term-drawbacks (math is boring sometimes). The brain constantly compares the undertaking against the best alternative – daydreaming, which has a lot of short-term utility. Comparing these two options is what feels effortful. The scene changes, a smartphone appears next to the study subject. Playing with it is lots of fun and carries higher utility than daydreaming but still less than doing the assigned task. However, solving the math problem now feels more effortful because the cost-benefit calculation has become a lot harder.
III The reward theory
Neither of these theories really convinced me, so here is a third one. Maarten Boksem, who is currently an Associate Professor of Marketing Management at the Rotterdam School of Management has investigated the topic extensively in his dissertation [11] and proposes a model that is a bit similar to Kurzban’s. For him, mental fatigue is inevitable and arises to signal that the current behavior might not be optimal and should be amended. Working on a boring task for hours is interpreted as a waste of energy and the lack of reward is seen as a sign that the employed strategy is not working. However, willpower can be restored by increasing the rewards for a task which changes the cost-benefit analysis and decreases fatigue. Boksem also investigates the neurochemical reasoning behind his model. The level of serotonin, a neurotransmitter, increases in the brain during prolonged effort. This inhibits the dopamine system and reduces motivation. The ratio of serotonin and dopamine hereby acts as a representation of the ratio of effort and reward.
What evidence does the author offer? He cites Bailey et al. [12] who gave rats a variety of drugs to decrease serotonin in the brain and showed that this made the animals become exhausted more quickly during treadmill running. Dopamine, however, was reduced when the rats became fatigued.
Additionally, Boksem et al. conducted a study (also found as [13]) to measure the impact of mental fatigue on reaction time and proneness to error. Over the course of two hours, nineteen participants had to perform a simple reaction task again and again while having their data collected. On a screen in front of them, a letter (either H or S) was shown. Depending on which it was, they had to press one of two buttons. This went on for seven intervals, each lasting 20 minutes. However, after the sixth, they were promised 25€ in case they performed well in the final round. Figure 1 shows the reaction time (RT) and errors in percent. It is noticeable, that from the first to the sixth round, RT and errors constantly get worse. Both improve after that but don’t manage to return to baseline.
The authors also wanted to know if mental fatigue can be observed by measuring electrical potentials in the brain. Using a 22-electrode EEG device, the error-related negativity or error negativity (ERN/Ne), a signal that is reported to be related to error detection, was monitored. Error detection is a central process in the context of action monitoring that aims to identify differences between expected and actual stimuli. If your car starts drifting to the side while driving on a straight road, this is being noticed and (hopefully) corrected by engaging the steering wheel. They found that Ne/ERN amplitude decreased from trial 1 to 6. The participants were told that they had to improve on both accuracy and speed, however, in practice, most seemed to select one of the two. Among those that increased their accuracy, Ne/ERN amplitude followed suit, the speed-improvement group showed no such effect. The fact, that no group managed to improve on both is a sign that there is more than a simple effort/reward calculation going on.
IV
Three theories, but only one can take the price home. Which one do you bet on? I have no expertise here, but for me, Boksem’s concept seems the most plausible. The glucose theory is sleek and intuitive, but the counter-arguments were so strong that I believe there might be something else going on there. Kurzban’s approach is interesting but in lieu of any hard evidence, I find it hard to evaluate it. Boksem substantiates his thoughts with neurological experiments and creates a round theory that will hopefully make it to the world cup next year. For me, Baumeister’s paper didn’t make intuitive sense because I didn’t see a reason why fun but cognitively demanding activities (e.g. video games) should use less glucose than boring stuff like studying.
This is psychology, so it might very well all be wrong but in case it is not, are there any practical conclusions to draw? It would have been easy to decrease fatigue with sugar consumption under the glucose model but Boksem’s reward/effort calculations seem a lot harder to influence. The most actionable approach I can think of is increasing the perceived reward of an action by promising yourself a treat afterwards.
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