The target article by Kurzban and colleagues is an intriguing and impressive attempt to integrate vast amounts of the cognitive, self-control, and neuroscience literature into an opportunity cost model of subjective effort. Here, we would like to propose that the explanatory power of the opportunity cost model could be further increased in two interrelated ways. First, rather than treating subjective mental effort solely as the output of a relative utility comparison among possible activities as proposed by Kurzban et al., subjective task effort may also enter as a cost input into the cost/benefit analysis that underlies the utility calculation of each activity involved. Second, and building on the first extension, the model might benefit from an inclusion of the idea that the judgment weights assigned to task effort as a cost may vary dynamically as a function of (a) temporary state reductions in executive functioning due to prolonged use of these capacities, (b) dispositional differences in executive functioning and related traits, and (c) meta-level theories about mental effort (e.g., theories of willpower).
In its current version, the model may have difficulties dealing with the following problems: First, because effort is treated as the result of a relative utility comparison of opportunity costs, people should go on almost infinitely (experiencing virtually no effort) pursuing a cognitively demanding option A when the value of this option is very high and no alternative option B comes close in utility. We argue, instead, that people may not only compare salient alternatives against each other in relative terms; rather, the net utility of each option, by itself, may already be the outcome of a benefit/cost consideration, with effort expenditure factoring in as a cost (see Table 1). We further assume that options with negative net utility are typically not enacted. The more demanding a given option – based on the relation between cognitive demand of the task and skill/cognitive executive capacity – the higher its perceived costs (in terms of task effort) and therefore the lower its net utility.
Table 1. Illustration of task effort as a cost input variable*
Most important, assuming that certain executive functions cannot be exerted infinitely without a state reduction in executive capacity and that people are motivated to monitor and conserve capacity (Muraven & Slessareva Reference Muraven and Slessareva2003), the weight (i.e., importance) assigned to task effort as a cost entering the utility computation may increase up to the point where the net utility of performing the task becomes negative (see Table 1, Case B). Such an extended version of the computational model would predict that people may value a given effortful activity more or less depending on the degree to which they perceive resource scarcity, even when all available alternatives are kept constant. In other words, it would account for why people may stop or choose to not engage in a demanding activity such as doing math problems in the absence of large opportunity costs associated with salient attractive alternatives. The current model tries to solve this problem by suggesting that there are more attractive alternatives (e.g., “daydreaming”) that are seen as opportunity costs in relation to the present activity, thus producing subjective feelings of effort that lead to disengagement from the present activity. A version that treats effort as a cost parameter with a dynamically varying judgment weight does not necessarily have to invoke such an alternative, because the cost-benefit ratio for the task itself may become negative (see Table 1, Case B).
The present model may also have difficulties explaining why people, in their daily lives or in lab studies, may deliberately choose alternative options at times that help to restore cognitive capacity, such as “taking a break” before returning to the focal activity at hand. In the current formulation of the model, such self-imposed periods of rest would constitute an irrational waste of processing time. We argue, instead, that, as state executive capacity is decreased over prolonged periods of task engagement, the weight assigned to effort as a cost increases. This change in the importance of effort dynamically influences the utility calculation process in a way such that the net utility of effortful activities decreases, whereas the net utility of activities instrumental for restoring capacity increases. By treating effort solely as the outcome of a relative utility comparison (rather than also as a possible input that affects computed utilities), Kurzban et al.'s model may have difficulties explaining why people would ever want to engage in an activity that has the sole purpose of restoring attentional and other capacities. For instance, drivers covering long distances should never feel motivated to take a break.
We believe that additional findings in the self-control literature can be explained (and that further predictions can be made) by considering the idea that the judgment weights assigned to effort as a cost input may vary dynamically and intra-individually. For example, people low in dispositional executive functioning, or need for cognition, or those who believe in limited willpower, may generally assign larger weights to effort as a cost than people dispositionally high in executive functioning (Kool et al. Reference Kool, McGuire, Rosen and Botvinick2010), high in need for cognition, and believing in unlimited willpower (Job et al. Reference Job, Dweck and Walton2010). Many resource-depletion findings (e.g., Muraven & Slessareva Reference Muraven and Slessareva2003) can be explained this way – as the effects of prior effortful task performance on the net utility of a subsequent effortful activity, mediated via a change in the weight assigned to task effort as a cost.
In sum, we believe that the phenomenology of effort as an output of a relative utility comparison among alternatives may need to be distinguished from the notion of task-specific effort as a potential cost input. In making everyday decisions about which courses of action to take and continue, people appear to care about the effortfulness of each of these activities in more than just a relative manner. How much they care about the effort dimension may depend on how resourceful they feel at a given point in time. When tired and faced with two effortful options that are otherwise high in benefits (e.g., exercising, doing the laundry) we may sometimes choose to not engage in such options at all.
The target article by Kurzban and colleagues is an intriguing and impressive attempt to integrate vast amounts of the cognitive, self-control, and neuroscience literature into an opportunity cost model of subjective effort. Here, we would like to propose that the explanatory power of the opportunity cost model could be further increased in two interrelated ways. First, rather than treating subjective mental effort solely as the output of a relative utility comparison among possible activities as proposed by Kurzban et al., subjective task effort may also enter as a cost input into the cost/benefit analysis that underlies the utility calculation of each activity involved. Second, and building on the first extension, the model might benefit from an inclusion of the idea that the judgment weights assigned to task effort as a cost may vary dynamically as a function of (a) temporary state reductions in executive functioning due to prolonged use of these capacities, (b) dispositional differences in executive functioning and related traits, and (c) meta-level theories about mental effort (e.g., theories of willpower).
In its current version, the model may have difficulties dealing with the following problems: First, because effort is treated as the result of a relative utility comparison of opportunity costs, people should go on almost infinitely (experiencing virtually no effort) pursuing a cognitively demanding option A when the value of this option is very high and no alternative option B comes close in utility. We argue, instead, that people may not only compare salient alternatives against each other in relative terms; rather, the net utility of each option, by itself, may already be the outcome of a benefit/cost consideration, with effort expenditure factoring in as a cost (see Table 1). We further assume that options with negative net utility are typically not enacted. The more demanding a given option – based on the relation between cognitive demand of the task and skill/cognitive executive capacity – the higher its perceived costs (in terms of task effort) and therefore the lower its net utility.
Table 1. Illustration of task effort as a cost input variable*
* The “cost” of effort varies dynamically as a function of situational and dispositional boundary conditions such as prior engagement in effortful activity, low executive functioning (i.e., low ability), or varying beliefs in willpower. Changes in the importance of effort are modeled as a change in the judgment weight assigned to effort as a cost.
Most important, assuming that certain executive functions cannot be exerted infinitely without a state reduction in executive capacity and that people are motivated to monitor and conserve capacity (Muraven & Slessareva Reference Muraven and Slessareva2003), the weight (i.e., importance) assigned to task effort as a cost entering the utility computation may increase up to the point where the net utility of performing the task becomes negative (see Table 1, Case B). Such an extended version of the computational model would predict that people may value a given effortful activity more or less depending on the degree to which they perceive resource scarcity, even when all available alternatives are kept constant. In other words, it would account for why people may stop or choose to not engage in a demanding activity such as doing math problems in the absence of large opportunity costs associated with salient attractive alternatives. The current model tries to solve this problem by suggesting that there are more attractive alternatives (e.g., “daydreaming”) that are seen as opportunity costs in relation to the present activity, thus producing subjective feelings of effort that lead to disengagement from the present activity. A version that treats effort as a cost parameter with a dynamically varying judgment weight does not necessarily have to invoke such an alternative, because the cost-benefit ratio for the task itself may become negative (see Table 1, Case B).
The present model may also have difficulties explaining why people, in their daily lives or in lab studies, may deliberately choose alternative options at times that help to restore cognitive capacity, such as “taking a break” before returning to the focal activity at hand. In the current formulation of the model, such self-imposed periods of rest would constitute an irrational waste of processing time. We argue, instead, that, as state executive capacity is decreased over prolonged periods of task engagement, the weight assigned to effort as a cost increases. This change in the importance of effort dynamically influences the utility calculation process in a way such that the net utility of effortful activities decreases, whereas the net utility of activities instrumental for restoring capacity increases. By treating effort solely as the outcome of a relative utility comparison (rather than also as a possible input that affects computed utilities), Kurzban et al.'s model may have difficulties explaining why people would ever want to engage in an activity that has the sole purpose of restoring attentional and other capacities. For instance, drivers covering long distances should never feel motivated to take a break.
We believe that additional findings in the self-control literature can be explained (and that further predictions can be made) by considering the idea that the judgment weights assigned to effort as a cost input may vary dynamically and intra-individually. For example, people low in dispositional executive functioning, or need for cognition, or those who believe in limited willpower, may generally assign larger weights to effort as a cost than people dispositionally high in executive functioning (Kool et al. Reference Kool, McGuire, Rosen and Botvinick2010), high in need for cognition, and believing in unlimited willpower (Job et al. Reference Job, Dweck and Walton2010). Many resource-depletion findings (e.g., Muraven & Slessareva Reference Muraven and Slessareva2003) can be explained this way – as the effects of prior effortful task performance on the net utility of a subsequent effortful activity, mediated via a change in the weight assigned to task effort as a cost.
In sum, we believe that the phenomenology of effort as an output of a relative utility comparison among alternatives may need to be distinguished from the notion of task-specific effort as a potential cost input. In making everyday decisions about which courses of action to take and continue, people appear to care about the effortfulness of each of these activities in more than just a relative manner. How much they care about the effort dimension may depend on how resourceful they feel at a given point in time. When tired and faced with two effortful options that are otherwise high in benefits (e.g., exercising, doing the laundry) we may sometimes choose to not engage in such options at all.