Commentary/Kurzhan et al.: An opportunity cost model of subjective effort and task performance An organism diat utilizes an opportunity cost model of effort expenditure requires the ability to rapidly adjust task engagement in response to information from tlie environment and^ intemal homeostasis monitors. The locus coemleus (LC) receives input from tlie anterior cingulate cortex and orbital frontal cortex, stmctures implicated in the evaluation of cost/benefit trade-of'fs and valuation, as weU as arousal-related inputs from the autonomie nervous system (Aston-Jones & Cohen 2005). Additionally, human and animal studies demonstrate diat prefrontal networks are sensitive to norepinephrine concentration (Robbins & Amsten 2009), widi optimal levels necessary for successful task performance. This literature advocates for continuous feedback between die LC and cortical stmctures estimating die utiUty of maintaining tlie current effort-aUocation policy. CriticaUy, topdown cortical signals and peripheral autonomie input may shift •tlie activity of die LC-NE system in a temporaUy relevant manner (Aston-Jones & Cohen 2005). For example, projections from the anterior cingulate cortex may shift tlie firing rate of die noradrenergic neuron population, in tum altering tlie level of norepinephrine in tlie cortex, which decreases stability of tlie current effort policy and promotes disengagement and selection of a new action plan (Aston-Jones & Cohen 2005; Sara & Bouret 2012). A system diat adaptively shifts among action contingencies, as proposed in prominent theories of LC-NE system function, is central to an opportunity cost model of effort. Theories of LCNE function broadly conceptualize its activity as shifting the balance of ex-ploratory versus exploitative behavior or mediating a global signal to reset brain networks involved in action selection (Aston-Jones & Cohen; Sara & Bouret 2012). Examining LC-NE system activity in humans is difflcult, due to the smaU size of the nucleus, its brainstem location and die feasibility of assessing cortical levels of norepinephrine in vivo. However, several functional neuroimaging studies have described pattems of activity in LC. An early study described pattems of activation in a putative LC region and right lateralized prefrontal regions diat appear to respond parametricaUy to task difficulty (Raizada & Poldrack, 2007). Aldiough consistent witli a connection between LC and lateral prefrontal self-control networks, the study lacked die spatial specificity necessary to attribute a specific role to die LC. A subsequent study claimed to pharmacologicaUy modulate LC activity (Minzenberg et al. 2008) but faced similar scmtiny about die precision of LC localization (Astafiev et al. 2010). Recendy, a group applied improved brainstem spatial alignment to conclude tliat activity in LC correlates with unexpected uncertainty in a decision-making task (Payzan-LeNestour et al. 2013), consistent widi a dieoretical model (Yu & Dayan 2005). Assessing die LC-NE system in humans remains a chaUenge, but recent studies point to a possible altemative solution. Several groups have demonstrated the utility of peripheral neurophysiological measurements, notably changes in pupu diameter, as an index of LC-NE system activity. As classicaUy described by Kalineman (1973) and revived by Jepma and Nieuwenhuis (2011), Ncissar et al. (2012), Eldar et al. (2013) and odiers, changes in pupu size appear linked to the noradrenergic arousal system and related to decision variables such as novelty and uncertainty diat are useful for a system estimating opportunity costs to control effort-allocation policy. As Kurzban and coUeagues note, a normative account of effort wül benefit from unification of executive and self-control literature. We propose diat validation of peripheral measurements of LC-NE activity and tlieir integration widi effortful tasks constitutes a wortliwhüe approach to test Kurzban et al.'s opportunity cost model. Evaluation of LC-NE activity in effort contingency, trade-off, and performance tasks wül provide key evidence to support or refute particular mechanisms by which valuation and control systems interact to shift behavior in accordance widi an opportunity cost model. Together widi paraUel investigations of other neuromodulatory systems, this work wiU provide the quantitative framework that a normative model of effort requires.
An expanded perspective on the role of effort phenomenology in motivation and performance doi:10.1017/S0140525X13001118 Daniel C. Molden Department of Psychology, Northwestern University, Evanston, IL 60208. [email protected] http://nortiiwestern.academia.edu/DanielMoiden
Abstract: Kurzban and colleagues propose that e.xperiences of effort alter motivations to persist during goal pursuit by highlighting costs of persistence. I expand this proposal by discussing how effort e.vperiences (a) not only influence, but can be influenced by motivations to persist on a goal; and (b) not only highlight costs that undermine persistence, but can also signal progress and increase persistence.
Declines in effort and performance foUowing sustained goal pursuit are frequendy explained in terms of people's limited resources for engaging in self-regulation (Muraven & Baumeister 2000). Aldiough many findings support such limited-resource explanations (see Hagger et al. 2010a), emerging evidence has produced a growing consensus diat changes in people's motivation, radier Öian their capacity for self-regulation, may be responsible for decreases in performance over time (Beedie & Lane 2012; Inzlicht & Schmeichel 2012; Molden et al. 2012). The target aiticle by Kuraban and coUeagues not only adds to diis consensus, but also provides a more detailed account of how such changes in motivation and performance arise. Perhaps the most novel and intriguing aspects of Kurzban et al.'s account of self-regulation is die proposed role of people's experiences of effort and fatigue on dieir motivations to persist widi a current task or goal. In this account, such experiences alter the perceived opportunity costs involved in maintaining diis goal versus pursuing an altemative goal, ajid dius shift motivations away from die present task and toward different endeavors. This opportunity cost mechanism helps to explain and integrate many findings from a variety of literatures. However, the phenomenology of effort is also connected to additional motivational processes that infiuence self-regulation and performance. Below, I review research that ülustrates these additional processes and extends Kurzban et al.'s motivational analysis. Detennining the perceived costs and benefits of particular outcomes is certairjy one of die primary routes dirough wliich motivations affect goal pursuit and perfonnance (see Molden & Higgins 2012). However, ajiotlier infiuence of motivation on goal pursuit is how it alters the experiences people have dining diis pursuit (Higgins 2006). That is, many motivational interventions diat boost perfomiance do not merely infiuence evaluations of the costs and benefits of different goals or outcomes, but instead change people's experiences of effort and engagement while puisuing diese outcomes. For example, much research has shown tliat goals involving feelings of autonomy and self-direction, radier than feelings of control and coercion, create greater engagement and enjoyment (Deci & Ryan 2000). Consistent with these general findings, people who perceive diat diey have autonomously chosen to perform vigüance-related self-control tasks (e.g., monitoring for tlie appearance of a particular stimulus) experience less fatigue and more energy, which then increases how long diey can successfuUy perform these tasks (Muraven et al. 2008; see also MoUer et al. 2006; Muraven 2008). Moreover, additional research has shown that when tlie strategies people employ during goal pursuit are motivationaUy compatible with their broader self^regulatoiy preferences, tliis creates experiences of regulatory fit (Higgins 2008). Such fit also increases engagement in and enjoyment of goal pursuit, which subsequently improves performance on self-control tasks involving vigilance (e.g., avoiding distraction) and resistance to tempting altematives (e.g., choosing fmit over chocolate as a snack; Freitas et al. 2002; Hong & Lee 2008).
BEHAVIORAL AND BRAIN SCIENCES (2013) 36:6
699
Commentary/Kurzhan et al.: An opportunity cost model of subjective effort and task performance The effects on self-regulation of experiences of engagement arising from autonomy or regulatory fit are broadly consistent with tîie centraf rofe tfiat Kurzban and coUeagues give to feeUngs' of effort and fatigue in goaf pursuit. However, these findings afso demonstrate that, just as experiences of effort can affect motivations to sustain perfonnance on current goals, so, too, can the broader motivationaf context in which a goaf is pursued affect perfonnance by influencing experiences of effort. Beyond direcdy altering experiences of effort during goaf pursuit, various motivationaf processes can afso affect seff-regufation and perfonnance by infiuencing how people interpret diese experiences (see Mofden & Dweck 2006). Tfiat is, afdiough peopfe may often attribute feeUngs of effort and fatigue to diminishing retums for the continued pursuit of a current goaf, and thus sfiift attention to other aftematives, research has afso shown that odier attributions for these feeUngs with different impUcations for seff-regufation and performance are possibfe. Indeed, some studies have even shown diat, in particufar contexts, experiences of effort are interpreted as signs of progress and sustain goaf pursuit. One cfear demonstration of how varying interpretations of effort experiences can dramaticaffy influence the effect these experiences have on subsequent seff-regufation and performance was provided by Gfarkson et af. (2010). When peopfe were fed to attribute feeUngs of effort to a superficiaf source unrefated to the pursuit of their primary goaf (e.g., the cofor of the paper on which their task instructions were printed), they no fonger showed subsequent decUnes in persistence or perfonnance. Furthermore, wfien they view effort as an instrumentaf part of achieving dieir desired goafs, peopfe dien interpret experiences of effort as signaUng progress toward goaf compfetion, and these experiences hefp sustain rather than undermine self-regufation and perfonnance (Labroo & Kim 2009; Miefe et af. 2011; Miefe & Mofden 2010). Thus, instead of highlighting growing opportunity costs, effort experiences can afso at times indicate that continued goaf pursuit is fikefy to yiefd benefits. The effects on seff-regufation of attributions for effort experiences are afso broadly consistent widi the important role that Kurzban and coHeagues give to effort phenomenology in explaining the maintenance of or disengagement from goaf pursuit. However, these findings afso demonstrate that effects of such phenomenology are not Umited to static considerations of opportunity costs but are instead aftered by peopfe's dynamic interpretations of their experiences of effort, engagement, or fatigue during seff-regufation. To summarize, Kurzban et af. have made a substantiaf contribution to the Uterature on seff-regufation and performance with tfieir anafysis of how peopfe's experiences of effort during goaf pursuit affect their Ukefihood of sustaining tfiis pursuit. Here, I expand tfiis contribution by noting that: (1) Experiences of effort are not simpfy determined by bottom-up evafuations of goaf progress, but can afso be influenced by top-down orientations that detennine the broader motivationaf context witliin wfiich tfie goaf is pureued. (2) Effort experiences can afford many other attributions beyond die rising opportunity costs associated widi continued pursuit of tfie same goaf, and, within mindsets where effort is direcdy Unked to progress, such experiences can even increase goaf commitment. These expansions broaden die scope of the model proposed by Kurzban et af. and make it appUcabfe to an even wider range of pfienomena.
Willpower is not synonymous with "executive function" doi:10.1017/S0140525X1300112X John Monterosso and Shan Luo Department of Psychology, University of Southern California, Los Angeles, CA 90089. [email protected] [email protected] http://dornsife.usc.edu/iabs/monterosso/
700
BEHAVIORAL AND BRAIN SCIENCES (2013) 36:6
Abstract: Kurzban et af. make a convincing case against the idea that wiflpower is a depfeting resource. However, they do not advance a positive account of wiffpower. Rather tfian treating "wilfpower" as a synonym of "executive function," we argue that tlie term willpower • should be designated for mechanisms individuals deploy to reduce dynamic inconsistency in theix behavior.
The typicaf effect-size of depletion experiments {~d = .6; Hagger et af. 2010a) is not the rigfit order of magnitude to go with the idea that diere is a Uteraf store of wilfpower that is being "used up." Nor is the fact that post-depletion, self-controf can be restored by receipt of a gift, or by a seff-affirmation (Schmeichef & Vohs 2009). Gompare seff-controf depfetion effects widi die actuaf muscfe fatigue from repeatedly Ufting a heavy weight-here total muscle faifure can easify and reUabfy be produced, and any effect of seff-affirmation is Ukefy to be modest. Afthough it remains to be seen whether Kurzban et af.'s modef has it just right, it is on its face a more pfausibfe account. However, we tfünk neither Baumeister et af. (2008) nor Kurzban and coUeagues characterize willpower usefuUy (afthough in faimess, onfy Baumeister and coUeagues seem to want to use this term). The phenomenon diat both deaf with is variousfy referred to as "executive function," "conscious processing," and as the output of "System 2" (Baumeister et af. 2008). The incongment condition of the Stroop fits weU, and is a standard depfetion paradigm. The task requires cofor naming, which competes with the automatic tendency to read fexicaf items. Tfiere is no question tfiat the Stroop Task is an interesting exampfe of an important category of mentaf functioning. But die term "wiffpower" has a more specific meaning-it is not a synonym for "executive function". In particufar, we believe tfiat the mecfianisms of wüfpower are directed at reducing the otherwise marked tendency most peopfe fiave to systematicaUy change their preferences over time. The case of addiction is Ufustrative. The criteria used in the United States for "substance dependence" and for "substance use disorder" incfude (parapfirasing from the Diagnostic and Statistical Manual of Mental Disorders TV-R) "faifed attempts to quit or moderate use" and "repeated episodes in which the individuaf uses more than she originaUy pfanned." In everyday use of the terms, these centraf features of addiction are considered stmggfes of "wiflpower" and of "seff-controf." What does the seff-controf stmggfe of die addict have in common widi an executive function task such as the Stroop? This is a point of some disagreement, but we suspect that tfie answer is not very much. First, peak performance on executive control tasks is observed in early adufdiood; performance decUnes dramatically with aging. If diis type of functioning were synonymous with "wiffpower," one woufd have reason to expect addiction to be a rare probfem among young adufts, but to increase in prevafence as peopfe age. But tfie opposite is observed, with prevafence higfiest in earfy adufdiood, and with a farge percentage of addicts "aging out" in mid to fate Ufe (AngUn et af. 1986). Second, there is a mismatch between the timescafe of faifures on the incongment Stroop and the seff-controf failures of an addict. When a person makes a mistake on the Stroop, sfie is succumbing to a reflexive tendency to read fexicaf items. If she is given an opportunity to sfow down, she wüf ffx her error. By contrast, when the cocaine addict who has been cfean for a montfi "faUs off the wagon," she may have to go to some fengths to get cocaine. It is not a momentary "oops" that is reUabfy corrected if she is given a moment to coUect fier diougfits. UnUke the participant performing the Stroop, the individual looking for cocaine is engaged in sustained goaf-directed action, and even compfex problem sofving. Of course, the situation of the addict fafUng off die wagon is so interesting because it is goaf-directed action sfie previousfy dismissed as undesirabfe, and whicfi she Ukefy will fater regret. Indeed, sfie may even beUeve sfie wiff regret it, even as she currendy devotes herself to obtaining the dmg. And diese are the critical features that define the domain of wiffpower/seff-controf
Copyright of Behavioral & Brain Sciences is the property of Cambridge University Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
An expanded perspective on the role of effort phenomenology in motivation and performance doi:10.1017/S0140525X13001118 Daniel C. Molden Department of Psychology, Northwestern University, Evanston, IL 60208. [email protected] http://nortiiwestern.academia.edu/DanielMoiden
Abstract: Kurzban and colleagues propose that e.xperiences of effort alter motivations to persist during goal pursuit by highlighting costs of persistence. I expand this proposal by discussing how effort e.vperiences (a) not only influence, but can be influenced by motivations to persist on a goal; and (b) not only highlight costs that undermine persistence, but can also signal progress and increase persistence.
Declines in effort and performance foUowing sustained goal pursuit are frequendy explained in terms of people's limited resources for engaging in self-regulation (Muraven & Baumeister 2000). Aldiough many findings support such limited-resource explanations (see Hagger et al. 2010a), emerging evidence has produced a growing consensus diat changes in people's motivation, radier Öian their capacity for self-regulation, may be responsible for decreases in performance over time (Beedie & Lane 2012; Inzlicht & Schmeichel 2012; Molden et al. 2012). The target aiticle by Kuraban and coUeagues not only adds to diis consensus, but also provides a more detailed account of how such changes in motivation and performance arise. Perhaps the most novel and intriguing aspects of Kurzban et al.'s account of self-regulation is die proposed role of people's experiences of effort and fatigue on dieir motivations to persist widi a current task or goal. In this account, such experiences alter the perceived opportunity costs involved in maintaining diis goal versus pursuing an altemative goal, ajid dius shift motivations away from die present task and toward different endeavors. This opportunity cost mechanism helps to explain and integrate many findings from a variety of literatures. However, the phenomenology of effort is also connected to additional motivational processes that infiuence self-regulation and performance. Below, I review research that ülustrates these additional processes and extends Kurzban et al.'s motivational analysis. Detennining the perceived costs and benefits of particular outcomes is certairjy one of die primary routes dirough wliich motivations affect goal pursuit and perfonnance (see Molden & Higgins 2012). However, ajiotlier infiuence of motivation on goal pursuit is how it alters the experiences people have dining diis pursuit (Higgins 2006). That is, many motivational interventions diat boost perfomiance do not merely infiuence evaluations of the costs and benefits of different goals or outcomes, but instead change people's experiences of effort and engagement while puisuing diese outcomes. For example, much research has shown tliat goals involving feelings of autonomy and self-direction, radier than feelings of control and coercion, create greater engagement and enjoyment (Deci & Ryan 2000). Consistent with these general findings, people who perceive diat diey have autonomously chosen to perform vigüance-related self-control tasks (e.g., monitoring for tlie appearance of a particular stimulus) experience less fatigue and more energy, which then increases how long diey can successfuUy perform these tasks (Muraven et al. 2008; see also MoUer et al. 2006; Muraven 2008). Moreover, additional research has shown that when tlie strategies people employ during goal pursuit are motivationaUy compatible with their broader self^regulatoiy preferences, tliis creates experiences of regulatory fit (Higgins 2008). Such fit also increases engagement in and enjoyment of goal pursuit, which subsequently improves performance on self-control tasks involving vigilance (e.g., avoiding distraction) and resistance to tempting altematives (e.g., choosing fmit over chocolate as a snack; Freitas et al. 2002; Hong & Lee 2008).
BEHAVIORAL AND BRAIN SCIENCES (2013) 36:6
699
Commentary/Kurzhan et al.: An opportunity cost model of subjective effort and task performance The effects on self-regulation of experiences of engagement arising from autonomy or regulatory fit are broadly consistent with tîie centraf rofe tfiat Kurzban and coUeagues give to feeUngs' of effort and fatigue in goaf pursuit. However, these findings afso demonstrate that, just as experiences of effort can affect motivations to sustain perfonnance on current goals, so, too, can the broader motivationaf context in which a goaf is pursued affect perfonnance by influencing experiences of effort. Beyond direcdy altering experiences of effort during goaf pursuit, various motivationaf processes can afso affect seff-regufation and perfonnance by infiuencing how people interpret diese experiences (see Mofden & Dweck 2006). Tfiat is, afdiough peopfe may often attribute feeUngs of effort and fatigue to diminishing retums for the continued pursuit of a current goaf, and thus sfiift attention to other aftematives, research has afso shown that odier attributions for these feeUngs with different impUcations for seff-regufation and performance are possibfe. Indeed, some studies have even shown diat, in particufar contexts, experiences of effort are interpreted as signs of progress and sustain goaf pursuit. One cfear demonstration of how varying interpretations of effort experiences can dramaticaffy influence the effect these experiences have on subsequent seff-regufation and performance was provided by Gfarkson et af. (2010). When peopfe were fed to attribute feeUngs of effort to a superficiaf source unrefated to the pursuit of their primary goaf (e.g., the cofor of the paper on which their task instructions were printed), they no fonger showed subsequent decUnes in persistence or perfonnance. Furthermore, wfien they view effort as an instrumentaf part of achieving dieir desired goafs, peopfe dien interpret experiences of effort as signaUng progress toward goaf compfetion, and these experiences hefp sustain rather than undermine self-regufation and perfonnance (Labroo & Kim 2009; Miefe et af. 2011; Miefe & Mofden 2010). Thus, instead of highlighting growing opportunity costs, effort experiences can afso at times indicate that continued goaf pursuit is fikefy to yiefd benefits. The effects on seff-regufation of attributions for effort experiences are afso broadly consistent widi the important role that Kurzban and coHeagues give to effort phenomenology in explaining the maintenance of or disengagement from goaf pursuit. However, these findings afso demonstrate that effects of such phenomenology are not Umited to static considerations of opportunity costs but are instead aftered by peopfe's dynamic interpretations of their experiences of effort, engagement, or fatigue during seff-regufation. To summarize, Kurzban et af. have made a substantiaf contribution to the Uterature on seff-regufation and performance with tfieir anafysis of how peopfe's experiences of effort during goaf pursuit affect their Ukefihood of sustaining tfiis pursuit. Here, I expand tfiis contribution by noting that: (1) Experiences of effort are not simpfy determined by bottom-up evafuations of goaf progress, but can afso be influenced by top-down orientations that detennine the broader motivationaf context witliin wfiich tfie goaf is pureued. (2) Effort experiences can afford many other attributions beyond die rising opportunity costs associated widi continued pursuit of tfie same goaf, and, within mindsets where effort is direcdy Unked to progress, such experiences can even increase goaf commitment. These expansions broaden die scope of the model proposed by Kurzban et af. and make it appUcabfe to an even wider range of pfienomena.
Willpower is not synonymous with "executive function" doi:10.1017/S0140525X1300112X John Monterosso and Shan Luo Department of Psychology, University of Southern California, Los Angeles, CA 90089. [email protected] [email protected] http://dornsife.usc.edu/iabs/monterosso/
700
BEHAVIORAL AND BRAIN SCIENCES (2013) 36:6
Abstract: Kurzban et af. make a convincing case against the idea that wiflpower is a depfeting resource. However, they do not advance a positive account of wiffpower. Rather tfian treating "wilfpower" as a synonym of "executive function," we argue that tlie term willpower • should be designated for mechanisms individuals deploy to reduce dynamic inconsistency in theix behavior.
The typicaf effect-size of depletion experiments {~d = .6; Hagger et af. 2010a) is not the rigfit order of magnitude to go with the idea that diere is a Uteraf store of wilfpower that is being "used up." Nor is the fact that post-depletion, self-controf can be restored by receipt of a gift, or by a seff-affirmation (Schmeichef & Vohs 2009). Gompare seff-controf depfetion effects widi die actuaf muscfe fatigue from repeatedly Ufting a heavy weight-here total muscle faifure can easify and reUabfy be produced, and any effect of seff-affirmation is Ukefy to be modest. Afthough it remains to be seen whether Kurzban et af.'s modef has it just right, it is on its face a more pfausibfe account. However, we tfünk neither Baumeister et af. (2008) nor Kurzban and coUeagues characterize willpower usefuUy (afthough in faimess, onfy Baumeister and coUeagues seem to want to use this term). The phenomenon diat both deaf with is variousfy referred to as "executive function," "conscious processing," and as the output of "System 2" (Baumeister et af. 2008). The incongment condition of the Stroop fits weU, and is a standard depfetion paradigm. The task requires cofor naming, which competes with the automatic tendency to read fexicaf items. Tfiere is no question tfiat the Stroop Task is an interesting exampfe of an important category of mentaf functioning. But die term "wiffpower" has a more specific meaning-it is not a synonym for "executive function". In particufar, we believe tfiat the mecfianisms of wüfpower are directed at reducing the otherwise marked tendency most peopfe fiave to systematicaUy change their preferences over time. The case of addiction is Ufustrative. The criteria used in the United States for "substance dependence" and for "substance use disorder" incfude (parapfirasing from the Diagnostic and Statistical Manual of Mental Disorders TV-R) "faifed attempts to quit or moderate use" and "repeated episodes in which the individuaf uses more than she originaUy pfanned." In everyday use of the terms, these centraf features of addiction are considered stmggfes of "wiflpower" and of "seff-controf." What does the seff-controf stmggfe of die addict have in common widi an executive function task such as the Stroop? This is a point of some disagreement, but we suspect that tfie answer is not very much. First, peak performance on executive control tasks is observed in early adufdiood; performance decUnes dramatically with aging. If diis type of functioning were synonymous with "wiffpower," one woufd have reason to expect addiction to be a rare probfem among young adufts, but to increase in prevafence as peopfe age. But tfie opposite is observed, with prevafence higfiest in earfy adufdiood, and with a farge percentage of addicts "aging out" in mid to fate Ufe (AngUn et af. 1986). Second, there is a mismatch between the timescafe of faifures on the incongment Stroop and the seff-controf failures of an addict. When a person makes a mistake on the Stroop, sfie is succumbing to a reflexive tendency to read fexicaf items. If she is given an opportunity to sfow down, she wüf ffx her error. By contrast, when the cocaine addict who has been cfean for a montfi "faUs off the wagon," she may have to go to some fengths to get cocaine. It is not a momentary "oops" that is reUabfy corrected if she is given a moment to coUect fier diougfits. UnUke the participant performing the Stroop, the individual looking for cocaine is engaged in sustained goaf-directed action, and even compfex problem sofving. Of course, the situation of the addict fafUng off die wagon is so interesting because it is goaf-directed action sfie previousfy dismissed as undesirabfe, and whicfi she Ukefy will fater regret. Indeed, sfie may even beUeve sfie wiff regret it, even as she currendy devotes herself to obtaining the dmg. And diese are the critical features that define the domain of wiffpower/seff-controf
Copyright of Behavioral & Brain Sciences is the property of Cambridge University Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
