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Kurzban et al. on opportunity cost models of mental fatigue and resource-based models of willpower

19 Post author: Kaj_Sotala 06 December 2013 09:54AM

An opportunity cost model of subjective effort and task performance (h/t lukeprog) is a very interesting paper on why we accumulate mental fatigue: Kurzban et al. suggest an opportunity cost model, where intense focus on a single task means that we become less capable of using our mental resources for anything else, and accumulating mental fatigue is part of a cost-benefit calculation that encourages us to shift our attention instead of monomaniacally concentrating on just one task which may not be the most rewarding possible. Correspondingly, the amount of boredom or mental fatigue we experience with a task should correspond with the perceived rewards from other tasks available at the moment. A task will feel more boring/effortful if there's something more rewarding that you could be doing instead (i.e. if the opportunity costs for pursuing your current task are higher), and if it requires exclusive use of cognitive resources that could also be used for something else.

This seems to make an amount of intuitive/introspective sense - I had a much easier time doing stuff without getting bored as a kid, when there simply wasn't much else that I could be doing instead. And it does roughly feel like I would get more quickly bored with things in situations where more engaging pursuits were available. I'm also reminded of the thing I noticed as a kid where, if I borrowed a single book from the library, I would likely get quickly engrossed in it, whereas if I had several alternatives it would be more likely that I'd end up looking at each for a bit but never really get around reading any of them.

An opportunity cost model also makes more sense than resource models of willpower which, as Kurzban quite persuasively argued in his earlier book, don't really fit together with the fact that the brain is an information-processing system. My computer doesn't need to use any more electricity in situations where it "decides" to do something as opposed to not doing something, but resource models of willpower have tried to postulate that we would need more of e.g. glucose in order to maintain willpower. (Rather, it makes more sense to presume that a low level of blood sugar would shift the cost-benefit calculations in a way that led to e.g. conservation of resources.)

This isn't just Kurzban et al's opinion - the paper was published in Behavioral and Brain Sciences, which invites diverse comments to all the papers that they publish. In this particular case, it was surprising how muted the defenses of the resource model were. As Kurzban et al point out in their response to responses:

As context for our expectations, consider the impact of one of the central ideas with which we were taking issue, the claim that “willpower” is a resource that is consumed when self-control is exerted. To give a sense of the reach of this idea, in the same month that our target article was accepted for publication Michael Lewis reported in Vanity Fair that no less a figure than President Barack Obama was aware of, endorsed, and based his decision- making process on the general idea that “the simple act of making decisions degrades one’s ability to make further decisions,” with Obama explaining: “I’m trying to pare down decisions. I don’t want to make decisions about what I’m eating or wearing. Because I have too many other decisions to make ” (Lewis 2012 ).

Add to this the fact that a book based on this idea became a New York Times bestseller (Baumeister & Tierney 2011 ), the fact that a central paper articulating the idea (Baumeister et al. 1998 ) has been cited more than 1,400 times, and, more broadly, the vast number of research programs using this idea as a foundation, and we can be forgiven for thinking that we would have kicked up something of a hornet’s nest in suggesting that the willpower-as-resource model was wrong. So we anticipated no small amount of stings from the large number of scholars involved in this research enterprise. These were our expectations before receiving the commentaries.

Our expectations were not met. Take, for example, the reaction to our claim that the glucose version of the resource argument is false (Kurzban 2010a ). Inzlicht & Schmeichel, scholars who have published widely in the willpower-as-resource literature, more or less casually bury the model with the remark in their commentary that the “mounting evidence points to the conclusion that blood glucose is not the proximate mechanism of depletion.” ( Malecek & Poldrack express a similar view.) Not a single voice has been raised to defend the glucose model, and, given the evidence that we advanced to support our view that this model is unlikely to be correct, we hope that researchers will take the fact that none of the impressive array of scholars submitting comments defended the view to be a good indication that perhaps the model is, in fact, indefensible. Even if the opportunity cost account of effort turns out not to be correct, we are pleased that the evidence from the commentaries – or the absence of evidence – will stand as an indication to audiences that it might be time to move to more profitable explanations of subjective effort.

While the silence on the glucose model is perhaps most obvious, we are similarly surprised by the remarkably light defense of the resource view more generally. As Kool & Botvinick put it, quite correctly in our perception: “Research on the dynamics of cognitive effort have been dominated, over recent decades, by accounts centering on the notion of a limited and depletable ‘resource’” (italics ours). It would seem to be quite surprising, then, that in the context of our critique of the dominant view, arguably the strongest pertinent remarks come from Carter & McCullough, who imply that the strength of the key phenomenon that underlies the resource model – two-task “ego-depletion” studies – might be considerably less than previously thought or perhaps even nonexistent. Despite the confidence voiced by Inzlicht & Schmeichel about the two-task findings, the strongest voices surrounding the model, then, are raised against it, rather than for it. (See also Monterosso & Luo , who are similarly skeptical of the resource account.)

Indeed, what defenses there are of the resource account are not nearly as adamant as we had expected. Hagger wonders if there is “still room for a ‘resource’ account,” given the evidence that cuts against it, conceding that “[t]he ego-depletion literature is problematic.” Further, he relies largely on the argument that the opportunity cost model we offer might be incomplete, thus “leaving room” for other ideas.

(I'm leaving out discussion of some commentaries which do attempt to defend resource models.)

Though the model still seems to be missing pieces - as one of the commentaries points out, it doesn't really address the fact that some tasks are more inherently boring than others. Some of it might be explained by the argument given in Shouts, Whispers, and the Myth of Willpower: A Recursive Guide to Efficacy (I quote the most relevant bit here), where the author suggests that "self-discipline" in some domain is really about sensitivity for feedback in that domain: a novice in some task doesn't really manage to notice the small nuances that have become so significant for an expert, so they receive little feedback for their actions and it ends up being a boring vigilance task. Whereas an expert will instantly notice the effects that their actions have on the system and get feedback of their progress, which in the opportunity cost model could be interpreted as raising the worthwhileness of the task they're working on. If we go with Kurzban et al.'s notion of us acquiring further information about the expected utility of the task we're working on as we continue working on it, then getting feedback from the task could possibly be read as a sign of the task being one in which we can expect to succeed in.

Another missing piece with the model is that it doesn't really seem to explain the way that one can come home after a long day at work and then feel too exhausted to do anything at all - it can't really be about opportunity costs if you end up so tired that you can't come up with ~any activity that you'd want to do.

Comments (15)

Comment author: Viliam_Bur 06 December 2013 10:32:42AM *  13 points [-]

Possible explanations for opportunity costs of feeling too exhausted to do anything at all:

a) The best action you should be doing now is to sleep or at least to take a nap, so your brain would process the information it has now and prepare itself for new information.

b) You are censoring the best action from your thoughts because it does not fit your idea of what you should be doing now. For example you feel that you should work on your personal projects, but your brain thinks you should drink some beer with your friends. When you say you are too exhausted to do anything, you are actually lying, because you are not too exhausted to drink beer with your friends; it is merely outside of your set of acceptable answers.

c) Your brain is wrong. For reasons that might make sense living in a jungle millenia ago, your brain is convinced that you should do X, which in reality is not an option, or is a bad option. All meaningful options are penalized because your brain insists that you should do X instead.

For example, if your job made you too exhausted, your brain may think the best action is to prevent going to the same job tomorrow. Which may be not realistic, or merely not what you want to think about.

Comment author: chairbender 11 December 2013 06:42:36AM *  5 points [-]

a) The best action you should be doing now is to sleep or at least to take a nap, so your brain would process the information it has now and prepare itself for new information

I don't think this is how Kurzban's model would explain it. In Kurzban's model, the "feeling of exhaustion" stems from one or more monitoring mechanisms causing aversive states (in response to trying to decide what to do). The monitoring mechanisms aren't causing the feeling of exhaustion so that you'll feel sleepy - they are just voting by causing aversive states, and Kaj_Sotala happens to interpret that feeling of the aversive states with the word "exhaustion" (which has certain unhelpful connotations and I think should be taboo'd in favor of "aversive state feelings").

c) Your brain is wrong. For reasons that might make sense living in a jungle millenia ago, your brain is convinced that you should do X, which in reality is not an option, or is a bad option. All meaningful options are penalized because your brain insists that you should do X instead. For example, if your job made you too exhausted, your brain may think the best action is to prevent going to the same job tomorrow. Which may be not realistic, or merely not what you want to think about.

I also don't think this applies the model correctly. The feeling of exhaustion would need to stem from aversive states from monitoring mechanisms that are working at the moment you get back from work and are deciding what to do next. Returning to work the next day is a very distant action, relative to all the activities your brain would be thinking about doing at that moment.

b) You are censoring the best action from your thoughts because it does not fit your idea of what you should be doing now. For example you feel that you should work on your personal projects, but your brain thinks you should drink some beer with your friends. When you say you are too exhausted to do anything, you are actually lying, because you are not too exhausted to drink beer with your friends; it is merely outside of your set of acceptable answers.

I think this is more how Kurzban's model would explain this situation. The bad feeling (which Kaj calls "exhaustion") would need to come from multiple monitoring mechanisms returning aversive states for evaluating various possible next actions (in this case, maybe working on projects, watching tv, browsing the internet, practicing, or studying).

It could be that there is no strong winner (so Kaj ends up feeling just the aversive states but not a clear idea of what to do next and has to spend more time feeling that exhaustion before a clear winner emerges). In this model, I think it would be possible for no strong winner to emerge even when there are immediately gratifying activities due to some monitoring mechanisms paying attention to some sort of executive function-centered value system (like "I should feel bad for doing <instantly gratifying activity>"). If that were the case, I would think Kaj might feel a sort of "oscillation" between deciding to do something instantly gratifying (which is generally a quick judgement for a brain to make) but then deciding not to after the executive function/value system evaluation results are returned (which I think generally takes longer to get a result from).

It could also be that Kaj's brain did actually reach a conclusion on what to do next, but either wasn't introspective enough to figure out what that was and put it into words or they meant the phrase "not doing anything at all" to be a catch-all for some unproductive but instantly gratifying action.

W.r.t. this seeming to occur after "a long day at work", I'm not really clear what is meant by "a long day".

Comment author: Kaj_Sotala 11 December 2013 11:47:24AM 1 point [-]

Great comment!

Comment author: Viliam_Bur 11 December 2013 10:37:11AM *  1 point [-]

The monitoring mechanisms aren't causing the feeling of exhaustion so that you'll feel sleepy - they are just voting by causing aversive states

Thank you, this distinction between "feeling sleepy as a mechanism to get more sleep" and "feeling sleepy as a crude mechanism to just stop doing whatever you are doing now" seems very useful! So I should generally treat sleepiness as a signal which means "stop doing what you are doing", without necessarily meaning "...and get some sleep".

Although a short rest or nap would probably not be harmful, because it does stop doing what I was doing, and provides me a time to reflect on my next actions. Short meditation would help too.

Comment author: chairbender 11 December 2013 05:42:20PM *  0 points [-]

Still, not quite. Basically, what Kurzban is saying is that that bad feeling that people attribute to "mental fatigue" is really just a residual feeling left over from the aversive-state votes of the monitoring mechanisms. It's not actually a way for your brain to try to communicate to you, at a conscious level, that you should do something different. You feeling that bad feeling is just a side-effect of that decision making process taking place (or, a decision that has already taken place). And, if I understand correctly, you'll feel that bad feeling more strongly when the votes from the monitoring mechanisms are more negative (which is why it generally feels harder to do things that are less immediately rewarding). If you are actually feeling like you need to sleep, though, I think that is a feeling that is actually not a part of this model.

Comment author: passive_fist 08 December 2013 11:28:04PM *  2 points [-]

I agree with your comment but it would be a lot better if you could say "Part of you thinks X and part of you thinks Y", instead of "You think X and your brain thinks Y".

Comment author: Gunnar_Zarncke 06 December 2013 11:01:43AM 1 point [-]

a) The best action you should be doing now is to sleep or at least to take a nap, so your brain would process the information it has now and prepare itself for new information.

This is actually a resource model type argument. Required sleep (or rather amount of wakeful time) is a limited resource which is depleeted by staging awake. It is not depleted or refilled linearly but a resource it is still.

Comment author: Viliam_Bur 06 December 2013 11:47:36AM *  5 points [-]

Here is an experiment with different predictions for the models:

Imagine a person doing some work for 8 hours. Based on experience from previous days, you know that if they get home, they will be "too exhausted to do anything". However, you ask them to stay and continue doing the same work for next 2 hours. As a reward, they will be allowed to leave the work 3 hours sooner tomorrow. (Let's suppose their time is fungible; i.e. they have nothing scheduled specifically for today evening).

Resource model: The person will not be able to work anymore, because their mental resources are depleted.

Opportunity cost model: The person will be able to continue to work, because this is the best option they have now.

(Keeping doing what they did would be the best choice; taking a nap and doing something else would be the next best choice; trying to switch to something completely different without taking the nap would be the worst choice.)

Comment author: Gunnar_Zarncke 06 December 2013 09:12:43PM 1 point [-]

I can tell you that I have worked definitely at my 'resource' limit a lot of times the last months and it definitely wasn't due to insufficient motivation but to plain exhaustion.

Actually when the motivation for the main task subsided I'd temporarily switch to a more rewarding intermediate task like lesswrong, thus the opportunity model itsn't wrong either.

But there comes a time when Isshoukenmei takes its toll. When you have to realize that your concentration is slipping after 14 hours and all further effort nearly ruins previous work.

But I have to agree that this amount of exhaustion is seldom nowadays and in your example of the 'exhausting' 8 hour work-day the 'exhaustion' most likely is from dissatisfaction, lack of reward or misapplication of pressure.

Comment author: alexvermeer 08 December 2013 12:20:11AM *  3 points [-]

This is exciting and interesting stuff. A good one-sentence summary from the paper:

In sum, many experiences, particularly the more or less unpleasant sensations discussed here (e.g., effort, boredom, fatigue), can be profitably thought of as resulting from (1) monitoring mechanisms that tally opportunity costs, which (2) cause an aversive state that corresponds in magnitude to the cost computed, which (3) enters into decision-making, acting as a kind of "vote," influencing the decision ultimately taken.

I'm trying to get my head around ways I could use this to sustain better and longer levels of focus, reduce boredom, etc. Two questions come to mind, that as far as I can tell have not been investigated in detail yet, and to which I don't have answers:

  1. What, exactly, are the sorts of things my brain decides are more important than what I'm currently doing? Is it things like "I'm not signaling the right things to the people around me", "need food", etc.?

  2. What are good ways to "reset" my internal monitoring mechanisms and thus return to a non-aversive state? I presume the answer is some kind of reward or positive feedback?

Basically, is it possible to trick this internal cost-benefit analysis into being focused for long periods of time?

Comment author: chairbender 11 December 2013 05:24:22AM 2 points [-]

Developing mindfulness skills (via mindfulness meditation, for example) probably wouldn't be a waste of time, if you want to improve your focus and decrease impulsive task-switching (and make doing productive things less unpleasant). I suspect that, in Kurzban's model, that feeling of "boredom" stems from a monitoring mechanism giving a negative evaluation of whatever it is you're doing.

When you practice mindfulness, you're basically practicing focusing on just one thing (breathing) and learning to shrug off and silence whatever comes to conscious attention that isn't relevant to that one thing. Applying Kurzban's model to mindfulness, you could say that you are improving your ability to, at will, mute those monitoring mechanisms and the aversive states that correspond to their outputs.

With meditation, when you're first starting out, you just attempt to notice when you are distracted and then return your thoughts to breathing. When you feel emotions (like boredom, which is a common one), you are supposed to note how intense it is and how long it lasts, then return to focusing on breathing. As you do this over and over, you start to get really, really fast at doing that attention re-direction/distraction suppression to the point where the distracting thoughts and emotions don't rise to a high enough level of intensity to cause you to shift your attention from your breathing (the distraction suppression becomes a kind of intuitive process that happens almost automatically).

In my personal experience, I've felt like it's much easier to stay focused on things (and not feel horribly bored when there's less productive but instantly gratifying alternatives) when I've kept up a steady meditation habit and made an effort to be mindful throughout the day. I've been trying to be aware of my feelings and how they fit with this model as I go about my day (which involves forcing myself to do a lot of things that aren't instantly gratifying but are long-term rewarding), and I've definitely felt like the mindfulness habits I've picked up work to negate or mute that feeling of boredom (when I actually remember to use them). When I'm trying to get started on some productive task, I really feel the aversive state at first, but I can use mindfulness to help eliminate it or it fades as I start to focus more and more on what I'm doing. When I have a problem, though (like I make a mistake when playing piano or am struggling to figure out some programming bug), I start to feel those aversive states (made even stronger by frustration) if I don't continue to apply mindfulness.

At the very least, meditation seems like it has helped improve my awareness of what my brain is doing at a given moment. Having Kurzban's model in mind when applying that introspection seems like it could be very useful for debugging undesirable behavior.

Comment author: philh 06 December 2013 03:17:20PM 3 points [-]

My computer doesn't need to use any more electricity in situations where it "decides" to do something as opposed to not doing something

Doesn't it? I thought that e.g. cpu-mining bitcoins would cost you more in electricity than it earns you in bitcoins. Or am I misinterpreting you?

Comment author: Kaj_Sotala 06 December 2013 05:38:58PM 0 points [-]

Yeah, that was bad wording from me. See the bit I linked there, it explains it better.

Comment author: Stabilizer 07 December 2013 02:38:39AM 2 points [-]

In this talk, Kurzban highlights that attempts to replicate the Baumeister willpower model have failed dramatically.

Comment author: ChristianKl 31 December 2013 05:19:18PM 0 points [-]

I think there are plenty of things that can sometimes work as resources.

Take tension in your back. If you sit to long in an unergonomic position in front of your desk, parts of your back will tense up. It will take some time for relaxation to get rid of that tension.

I think similar effects happen when you suppress emotions. Just because you have finished a task doesn't mean that your brain isn't still dealing with the emotions that the task raised.