Effort-based Decisions Research Articles

Perceived fatigue does not alter effort-based decision making but does undermine confidence in the ability to perform physical actions.

Fatigue may affect the decision to deploy effort (cost) for a given rewarded outcome (benefit). However, it remains unclear whether these fatigue-associated changes can be attributed to simply feeling fatigued. To investigate this question, twenty-two healthy males made a series of choices between two rewarded options: a fixed, no effort option, where no physical effort was required to obtain a set, low reward vs. a variable, effortful option, in which both the physical effort requirements (i.e. different durations of a sustained contraction performed in the lower limbs) and rewards (i.e. greater monetary incentives) was varied. Effort-based choices were made under two conditions: 1) a rested (control) state, (2) a pre-induced state of perceived fatigue, evoked through physical exertion in the upper-limbs, thus controlling for the physical manifestation of fatigue (i.e. decline in muscular force production) on the decision process. Though prior physical exertion increased the perception of fatigue, participants choice behaviour did not significantly differ between control and fatigue conditions. Across both conditions, participants demonstrated an anticipated aversion to effort, with greater effort requirements reducing the decision to engage in actions associated with higher rewards. However, in the fatigue state only, decision time was prolonged and self-reported confidence in individuals' ability to perform high effort actions was reduced. The findings suggest that a perceived state of fatigue does not necessarily alter cost/benefit comparisons within effort-based decisions, but may introduce greater uncertainty within choice and reduce self-confidence. These findings evidence altered evaluative processes during decision making under conditions of fatigue.

A computational approach to understanding effort-based decision-making in depression.

Motivational dysfunction is a core feature of depression, and can have debilitating effects on everyday function. However, it is unclear which disrupted cognitive processes underlie impaired motivation, and whether impairments persist following remission. Decision-making concerning exerting effort to collect rewards offers a promising framework for understanding motivation, especially when examined with computational tools which can offer precise quantification of latent processes. Effort-based decision-making was assessed using the Apple Gathering Task, in which participants decide whether to exert effort via a grip-force device to obtain varying levels of reward; effort levels were individually calibrated and varied parametrically. We present a comprehensive computational analysis of decision-making, initially validating our model in healthy volunteers (N=67), before applying it in a case-control study including current (N=41) and remitted (N=46) unmedicated depressed individuals, and healthy volunteers with (N=36) and without (N=57) a family history of depression. Four fundamental computational mechanisms that drive patterns of effort-based decisions, which replicated across samples, were identified: an overall bias to accept effort challenges; reward sensitivity; and linear and quadratic effort sensitivity. Traditional model-agnostic analyses showed that both depressed groups showed lower willingness to exert effort. In contrast with previous findings, computational analysis revealed that this difference was driven by lower effort acceptance bias, but not altered effort or reward sensitivity. This work provides insight into the computational mechanisms underlying motivational dysfunction in depression. Lower willingness to exert effort could represent a trait-like factor contributing to symptoms, and might represent a fruitful target for treatment and prevention.

Effort Foraging Task reveals positive correlation between individual differences in the cost of cognitive and physical effort in humans

Effort-based decisions, in which people weigh potential future rewards against effort costs required to achieve those rewards involve both cognitive and physical effort, though the mechanistic relationship between them is not yet understood. Here, we use an individual differences approach to isolate and measure the computational processes underlying effort-based decisions and test the association between cognitive and physical domains. Patch foraging is an ecologically valid reward rate maximization problem with well-developed theoretical tools. We developed the Effort Foraging Task, which embedded cognitive or physical effort into patch foraging, to quantify the cost of both cognitive and physical effort indirectly, by their effects on foraging choices. Participants chose between harvesting a depleting patch, or traveling to a new patch that was costly in time and effort. Participants’ exit thresholds (reflecting the reward they expected to receive by harvesting when they chose to travel to a new patch) were sensitive to cognitive and physical effort demands, allowing us to quantify the perceived effort cost in monetary terms. The indirect sequential choice style revealed effort-seeking behavior in a minority of participants (preferring high over low effort) that has apparently been missed by many previous approaches. Individual differences in cognitive and physical effort costs were positively correlated, suggesting that these are perceived and processed in common. We used canonical correlation analysis to probe the relationship of task measures to self-reported affect and motivation, and found correlations of cognitive effort with anxiety, cognitive function, behavioral activation, and self-efficacy, but no similar correlations with physical effort.

Preferences for seeking effort or reward information bias the willingness to work

Research suggests that the temporal order in which people receive information about costs and benefits whilst making decisions can influence their choices. But, do people have a preference for seeking information about costs or benefits when making effort-based decisions, and does this impact motivation? Here, participants made choices about whether to exert different levels of physical effort to obtain different magnitudes of reward, or rest for low reward. Prior to each effort-based choice, they also had to decide which information they wanted to see first: how much physical effort would be required, or how large the reward would be. We found no overall preference for seeking reward or effort information first, but motivation did change when people saw reward or effort information first. Seeking effort information first, both someone’s average tendency to do so and their choice to see effort first on a given trial, was associated with reductions in the willingness to exert higher effort. Moreover, the tendency to prefer effort information first was associated with reduced vigorous exercise and higher levels of fatigue in everyday life. These findings highlight that preferences for seeking effort information may be a bias that reduces people’s willingness to exert effort in the lab and in everyday life.

Working through negativity: The influence of affective states on effort-based decision-making

Affective states can influence a range of cognitive outcomes, such as decision-making. However, the effect of valence and arousal state inductions on effort-based decision-making is unclear. This study employed a mixed design in which all participants viewed low and high-arousal images, and participants were randomized to either a neutral, positive, or negative valence image manipulation. Participants repeatedly viewed a valenced-image and then completed a trial of the Effort Expenditure for Rewards Task (EFfRT). Results of Experiment 1 (N = 197) demonstrated that a valence induction manipulation influenced effort-based decision-making. Individuals in the negative valence condition chose fewer high-effort, difficult options than those in the neutral and positive valence conditions. Experiment 2 (N = 226) sought to explore the interplay between affective states and motivation on effort-based decision-making. Results of Experiment 2 replicated the finding that negative affective states impair willingness to engage in effortful tasks and showed that negative affect moderated the relationship between intrinsic motivation and willingness to exert effort. Self-reported arousal ratings, but not valence ratings, were also predictive of effort-based decisions. This work demonstrates that affective states may alter the cost of effort expenditure for potential rewards. Negative valence weakens one's volition to exert physical effort to obtain a monetary reward.

The Impact of Cognitive and Physical Effort Exertion on Physical Effort Decisions: A Pilot Experiment.

Research suggests that cognitive fatigue has a negative impact on physical activity participation. However, the mechanisms underlying this effect are yet unclear. Using an effort-based decision-making paradigm, we examined whether individuals weigh physical effort-costs more strongly when they are cognitively or physically fatigued. Twenty university students visited the lab on three occasions. On each visit, participants underwent a manipulation that was designed to either induce cognitive fatigue (i.e., 2-back task), physical fatigue (i.e., handgrip exercise), or served as a control condition (i.e., documentary watching). After the manipulations, participants performed an effort-based decision-making task in which they decided for 125 offers whether they accepted the offer to exert the required level of physical effort to obtain rewards that varied in value. The probability to accept offers declined with increasing effort requirements whereas the general probability to accept offers was not reduced by any of the experimental conditions. As expected, the decline in accepted offers with increasing effort requirements was stronger after prolonged exertion of physical effort compared to the control condition. Unexpectedly, this effect was not found after exerting cognitive effort, and exploratory analyses revealed that the impact of physical effort exertion on physical effort-based decisions was stronger than that of cognitive effort exertion. These findings suggest that people weight future physical effort-costs more strongly after exerting physical effort, whereas we could not find any evidence for this after exerting cognitive effort. We discuss multiple explanations for this discrepancy, and outline possibilities for future research.

Relationship of ventral striatum activation during effort discounting to clinical amotivation severity in schizophrenia

Motivational deficits play a central role in disability due to negative symptoms of schizophrenia (SZ), but limited pathophysiological understanding impedes critically needed therapeutic development. We applied an fMRI Effort Discounting Task (EDT) that quantifies motivation using a neuroeconomic decision-making approach, capturing the degree to which effort requirements produce reductions in the subjective value (SV) of monetary reward. An analyzed sample of 21 individuals with SZ and 23 group-matched controls performed the EDT during fMRI. We hypothesized that ventral striatum (VS) as well as extended brain motivation circuitry would encode SV, integrating reward and effort costs. We also hypothesized that VS hypoactivation during EDT decisions would demonstrate a dimensional relationship with clinical amotivation severity, reflecting greater suppression by effort costs. As hypothesized, VS as well as a broader cortico-limbic network were activated during the EDT and this activation correlated positively with SV. In SZ, activation to task decisions was reduced selectively in VS. Greater VS reductions correlated with more severe clinical amotivation in SZ and across all participants. However, these diagnosis and amotivation effects could not be explained by the response to parametric variation in reward, effort, or model-based SV. Our findings demonstrate that VS hypofunction in schizophrenia is manifested during effort-based decisions and reflects dimensional motivation impairment. Dysfunction of VS impacting effort-based decision-making can provide a target for biomarker development to guide novel efforts to assess and treat disabling amotivation.

Reconciling psychological and neuroscientific accounts of reduced motivation in aging.

Motivation is a hallmark of healthy aging, but the motivation to engage in effortful behavior diminishes with increasing age. Most neurobiological accounts of altered motivation in older adults assume that these deficits are caused by a gradual decline in brain tissue, while some psychological theories posit a switch from gain orientation to loss avoidance in motivational goals. Here, we contribute to reconcile the psychological and neural perspectives by providing evidence that the frontopolar cortex (FPC), a brain region involved in cost–benefit weighting, increasingly underpins effort avoidance rather than engagement with age. Using anodal transcranial direct current stimulation together with effort–reward trade-offs, we find that the FPC’s function in effort-based decisions remains focused on cost–benefit calculations but appears to switch from reward-seeking to cost avoidance with increasing age. This is further evidenced by the exploratory, independent analysis of structural brain changes, showing that the relationship between the density of the frontopolar neural tissue and the willingness to exert effort differs in young vs older adults. Our results inform aging-related models of decision-making by providing preliminary evidence that, in addition to cortical thinning, changes in goal orientation need to be considered in order to understand alterations in decision-making over the life span.

Neural and computational mechanisms of momentary fatigue and persistence in effort-based choice

From a gym workout, to deciding whether to persevere at work, many activities require us to persist in deciding that rewards are ‘worth the effort’ even as we become fatigued. However, studies examining effort-based decisions typically assume that the willingness to work is static. Here, we use computational modelling on two effort-based tasks, one behavioural and one during fMRI. We show that two hidden states of fatigue fluctuate on a moment-to-moment basis on different timescales but both reduce the willingness to exert effort for reward. The value of one state increases after effort but is ‘recoverable’ by rests, whereas a second ‘unrecoverable’ state gradually increases with work. The BOLD response in separate medial and lateral frontal sub-regions covaried with these states when making effort-based decisions, while a distinct fronto-striatal system integrated fatigue with value. These results provide a computational framework for understanding the brain mechanisms of persistence and momentary fatigue.

Causal role of lateral prefrontal cortex in mental effort and fatigue.

Dorsolateral prefrontal cortex (DLPFC) is well‐known for its role in exerting mental work, however the contribution of DLPFC for deciding whether or not to engage in effort remains unknown. Here, we assessed the causal role of DLPFC in effort‐based decision making. We disrupted functioning of DLPFC with noninvasive brain stimulation before participants repeatedly decided whether to exert mental effort in a working memory task. We found the same DLPFC subregion involved in mental effort exertion to influence also effort‐based decisions: First, it enhanced effort discounting, suggesting that DLPFC may signal the capacity to successfully deal with effort demands. Second, a novel computational model integrating the costs of enduring effort into the effort‐based decision process revealed that DLPFC disruption reduced fatigue after accumulated effort exertion, linking DLPFC activation with fatigue. Together, our findings indicate that in effort‐based decisions DLPFC represents the capacity to exert mental effort and the updating of this information with enduring time‐on‐task, informing theoretical accounts on the role of DLPFC in the motivation to exert mental effort and the fatigue arising from it.

Chemogenetic Modulation and Single-Photon Calcium Imaging in Anterior Cingulate Cortex Reveal a Mechanism for Effort-Based Decisions.

The ACC is implicated in effort exertion and choices based on effort cost, but it is still unclear how it mediates this cost-benefit evaluation. Here, male rats were trained to exert effort for a high-value reward (sucrose pellets) in a progressive ratio lever-pressing task. Trained rats were then tested in two conditions: a no-choice condition where lever-pressing for sucrose was the only available food option, and a choice condition where a low-value reward (lab chow) was freely available as an alternative to pressing for sucrose. Disruption of ACC, via either chemogenetic inhibition or excitation, reduced lever-pressing in the choice, but not in the no-choice, condition. We next looked for value coding cells in ACC during effortful behavior and reward consumption phases during choice and no-choice conditions. For this, we used in vivo miniaturized fluorescence microscopy to reliably track responses of the same cells and compare how ACC neurons respond during the same effortful behavior where there was a choice versus when there was no-choice. We found that lever-press and sucrose-evoked responses were significantly weaker during choice compared with no-choice sessions, which may have rendered them more susceptible to chemogenetic disruption. Together, findings from our interference experiments and neural recordings suggest that a mechanism by which ACC mediates effortful decisions is in the discrimination of the utility of available options. ACC regulates these choices by providing a stable population code for the relative value of different options.SIGNIFICANCE STATEMENT The ACC is implicated in effort-based decision-making. Here, we used chemogenetics and in vivo calcium imaging to explore its mechanism. Rats were trained to lever press for a high-value reward and tested in two conditions: a no-choice condition where lever-pressing for the high-value reward was the only option, and a choice condition where a low-value reward was also available. Inhibition or excitation of ACC reduced effort toward the high-value option, but only in the choice condition. Neural responses in ACC were weaker in the choice compared with the no-choice condition. A mechanism by which ACC regulates effortful decisions is in providing a stable population code for the discrimination of the utility of available options.

Redefining the relationship between effort and reward: Choice-execution model of effort-based decisions

Neuroscientific studies reliably demonstrate that rewards play a crucial role in guiding our choices when confronted with different effortful actions we could make. At the same time, psychological and economic research shows that effort we exert is not reliably predicted by the rewards we end up receiving. Why the mismatch between the two lines of evidence? Inspired by neuroscientific literature, we argue that value-based models of decision-making expose the complexity of the relationship between effort and reward, which changes between two crucial stages of the effort-based decision making process: Choice (i.e. action selection) and Execution (i.e. action execution involving actual effort exertion). To test this assumption, in the present study we set up two experiments (E1: N = 72, E2: N = 87), using a typical neuroscientific effort-based decision-making task. The findings of these experiments reveal that when making prospective choices, rewards do guide the level of effort people are prepared to exert, consistent with typical findings from Neuroscience. At a later stage, during execution of effortful actions, performance is determined by the actual amount of effort that needs to be exerted, consistent with psychological and behavioral economic research. We use the model we tested and the findings we generated to highlight critical new insights into effort-reward relationship, bringing different literatures together in the context of questions regarding what effort its, and the role that values play.

Effort-based decision making varies by smoking status.

A reduced willingness to perform effort based on the magnitude and probability of potential rewards has been associated with diminished dopamine function and may be relevant to chronic drug use. Here, we investigated the influence of smoking status on effort-based decisions. We hypothesized that smokers would make fewer high-effort selections than ex-smokers and never-smokers. Current smokers (n = 25), ex-smokers (≥ 1year quit, n = 23), and never-smokers (n = 19) completed the Effort Expenditure for Rewards Task in which participants select between low-effort and high-effort options to receive monetary rewards at varying levels of reward magnitude, probabilityand expected value. Overall, participants selected more high-effort options as potential reward magnitude and expected value increased. Smokers did not make fewer high-effort selections overall, but smokers were less sensitive to the changes in magnitude, probability, and expected value compared to never-smokers. Smokers were also less sensitive to the changes in probability and expected value, but not magnitude, compared to ex-smokers. Among smokers and ex-smokers, less nicotine dependence was associated with an increased likelihood of high-effort selections. These results demonstrate the relevance of smoking status to effort-based decisions and suggest that smokers have diminished sensitivity to nondrug reward value. Among ex-smokers, greater pre-existing sensitivity to reward value may have been conducive to smoking cessation, or sensitivity was improved by smoking cessation. Future prospective studies can investigate whether effort-related decision making is predictive of smoking initiation or cessation success. Willingness to perform effort to achieve a goal and sensitivity to changes in reward value are important aspects of motivation. These results showed that smokers have decreased sensitivity to changes in effort-related reward probability and expected value compared to ex-smokers and never-smokers. Potentially, improved sensitivity to rewards among ex-smokers may be a cause or consequence of smoking cessation. These findings may help explain why some smokers are able to achieve long-term abstinence.

Strive to Win or Not to Lose? Age-Related Differences in Framing Effects on Effort-Based Decision-Making.

This study sought to assess how framing effects modulate age-related differences in effort-based decision-making. Consistent with the selection, optimization, and compensation (SOC) model's loss prevention account of aging, we predicted that older adults would be more willing to select high-effort options in loss contexts than gain contexts. Older and younger adults completed the effort expenditure for rewards task (EEfRT) in either a gain or loss context. The EEfRT is an effort-based decision-making paradigm in which participants choose between a low-effort, "easy" option and a high-effort, "hard" option for several trials. The probability and value of an outcome varies on a trial-by-trial basis. The results supported our prediction and the SOC model. Older adults chose more high-effort, difficult options in loss frames than gain frames. Older adults also chose more low-effort, easy options than younger adults in gain contexts, but did not differ from younger adults in loss contexts. These findings demonstrate that framing effects impact older adults' effort-based decisions. Older adults appear willing to incur a greater "cost" in the form of effort to prevent a loss than to attain a reward.

Asymmetric valuation of gains and losses in effort-based decision making.

Our decisions are often swayed by a desire to avoid losses over a desire to acquire gains. While loss aversion has been confirmed for decisions about money or commodities, it is unclear how individuals generally value gains relative to losses in effort-based decisions. For example, do individuals avoid greater work more than they seek out less work? We examined this question in the context of physical effort, using an arm-reaching task in which decreased effort was framed as a gain and increased effort was framed as a loss. Subjects performed reaching movements against different levels of resistance that increased or decreased the effort demands of the reaches. They then chose to accept or reject various lotteries, each with a possibility of performing less effortful reaches and a possibility of performing more effortful reaches, compared to the certain outcome of performing reaches against a fixed reference level of effort. Subjects avoided higher effort conditions more than they sought lower effort conditions, demonstrating asymmetric valuation of gains and losses. Using prospect theory, we explored various model formulations to determine subject-specific valuation of effort in these mixed gambles. A nonlinear model of effort valuation demonstrating increasing sensitivity to absolute effort best described the effort lottery choices. In contrast to the loss-aversion observed in financial decisions, there was no evidence of loss aversion in effort-based decisions. Rather, we observed moderate relief-seeking behavior. This model confirms that gains and losses are valued asymmetrically. This is due to the combined effects of increasing sensitivity to absolute effort and moderate relief-seeking, leading to a net effect of greater avoidance of higher effort. Asymmetric valuation was magnified on a later day of testing. In contrast, subjects were loss-averse in a comparable financial task. We suggest that consideration of nonlinear effort valuation can inform future studies of sensorimotor control and exercise motivation.

Understanding the cognitive miser: Cue-utilization in effort-based decision making

The notion that individuals adapt their behaviors in ways that are sensitive to the effortfulness of cognitive processing is pervasive in psychology. In the current set of experiments, we provide a test of a cue-utilization account of how individuals decide which course of action is more or less effortful. In particular, we contrast the influences of time costs and demands on executive control with the influence of an available effort cue. Using a variant of the demand selection task (DST) that specifically focused on making effort-based decisions, we provide evidence that effort-based decisions can be dissociated from both time costs and demands on executive control in a manner predicted by a cue-utilization account.

Methylphenidate increases willingness to perform effort in adults with ADHD

BackgroundA reduced willingness to perform effort based on the magnitude and probability of potential rewards has been associated with diminished dopamine function and may be relevant to attention-deficit/hyperactivity disorder (ADHD). Here, we investigated the influence of ADHD status and methylphenidate on effort-based decisions. We hypothesized that ADHD participants would make fewer high-effort selections than non-ADHD subjects, and that methylphenidate would increase the number of high-effort selections. Furthermore, we hypothesized there would be associations among ADHD severity and methylphenidate-related changes in effort-based and attentional performance across all participants. Methods and participantsADHD (n = 23) and non-ADHD (n = 23) adults completed the Effort Expenditure for Rewards Task in which participants select between low-effort and high-effort options to receive monetary rewards at varying levels of reward magnitude and probability. A test of attentional performance was also completed. ResultsOverall, participants made more high-effort selections as potential reward magnitude and probability increased. ADHD participants did not make fewer high-effort selections than non-ADHD participants, but ADHD participants showed greater methylphenidate-related increases in high-effort selections. ADHD participants had worse attentional performance than non-ADHD participants. ADHD severity was associated with methylphenidate-related changes in high-effort selections, but not changes in attentional performance. ConclusionsThese results indicate that methylphenidate increases the willingness to perform effort in individuals with ADHD, possibly due to disorder-related motivational deficits. This provides support for theories of insufficient effort allocation among individuals with ADHD.Trial registration: Clinicaltrials.gov Identifier, NCT02630017.

Computational modelling reveals distinct patterns of cognitive and physical motivation in elite athletes

Effort can be perceived both cognitively and physically, but the computational mechanisms underlying the motivation to invest effort in each domain remain unclear. In particular, it is unknown whether intensive physical training is associated with higher motivation specific to that domain, or whether it is accompanied by corresponding changes in cognitive motivation. Here, we tested a group of elite Oxford University rowers, and compared their behaviour to matched non-athletic controls. We trained participants on two tasks involving cognitive or physical effort. They then decided between a baseline low level of effort for low reward, versus higher levels of effort for higher rewards. Separate choices were made for the cognitive and physical tasks, which allowed us to computationally model motivation in each domain independently. As expected, athletes were willing to exert greater amounts of physical effort than non-athletes. Critically, however, the nature of cognitive effort-based decisions was different between groups, with a concave pattern of effort discounting for athletes but a convex pattern for non-athletes. These data suggest that the greater physical drive in athletes is accompanied by fundamentally different patterns of cognitive effort discounting, and suggests a complex relationship between motivation in the two domains.

Exposure to bright light biases effort-based decisions.

Secreted in the evening and the night, melatonin suppresses activity of the mesolimbic dopamine pathway, a brain pathway involved in reward processing. However, exposure to bright light diminishes-or even prevents-melatonin secretion. Thus, we hypothesized that reward processing, in the evening, is more pronounced in bright light (vs. dim light). Healthy human participants carried out three tasks that tapped into various aspects of reward processing (effort expenditure for rewards task [EEfRT]; two-armed bandit task [2ABT]; balloon analogue risk task [BART). Brightness was manipulated within-subjects (bright vs. dim light), in separate evening sessions. During the EEfRT, participants used reward-value information more strongly when they were exposed to bright light (vs. dim light). This finding supported our hypothesis. However, exposure to bright light did not significantly affect task behavior on the 2ABT and the BART. While future research is necessary (e.g., to zoom in on working mechanisms), these findings have potential implications for the design of physical work environments. (PsycINFO Database Record

Supplemental Material for Exposure to Bright Light Biases Effort-Based Decisions

Supplemental Material for Exposure to Bright Light Biases Effort-Based Decisions