After a pair of self-control-intensive tasks, sucrose swishing improves subsequent working memory performance

Physiological Factors Which Influence Cognitive Performance in Military Personnel

OBJECTIVE

To identify and detail physiological factors that influence cognition in military personnel.

BACKGROUND

Maintenance of cognitive and task performance is important under several scenarios, none more so than in a military context. Personnel are prepared for and trained to tolerate many of the stressors they encounter; however, consideration of stressors typically extends only as far as the physical, psychological, and environmental requirements of a given task. While considering these factors certainly characterizes the broader picture, several physiological states and traits can influence cognition and thus, should also be considered.

METHOD

A systematic review of the electronic databases Medline (PubMed), EMBASE (Scopus), PsycINFO, and Web of Science was conducted from inception up to January 2019. Eligibility criteria included current military personnel, an outcome of cognition, and the assessment of a physiological factor.

RESULTS

The search returned 60,564 records, of which 60 were included in the review. Eleven studies examined the impact of demographic factors on cognition, 16 examined fatigue, 10 investigated nutrition, and 24 the impact of biological factors on cognitive performance.

CONCLUSION

Factors identified as having a positive impact on cognition include aerobic fitness, nutritional supplementation, and visual acuity. In contrast, factors identified as having a negative impact include fatigue arising from sustained operations, dehydration, undernutrition, and an exaggerated physiological stress response to a cognitive task or a stressor. A further subset of these factors was considered modifiable.

APPLICATION

The modifiable factors identified provide avenues for training and preparation to enhance cognition in ways previously unconsidered.

Sweet Nothings

Abstract. Prior research has suggested that circulating levels of glucose in the bloodstream help to determine success at self-control. However, this idea has been challenged on multiple grounds. The current research added new evidence to the debate by testing (1) the extent to which exercising self-control reduces blood glucose levels, (2) whether consuming glucose, rinsing the mouth with glucose, or consuming aspartame (a sugar substitute) increases blood glucose levels, and (3) the extent to which measured blood glucose levels relate to emotional responding, delay discounting, and cognitive control, respectively. We found no evidence that blood glucose levels influence or are influenced by self-control.

Why has evolution not selected for perfect self-control?

Self-control refers to the ability to deliberately reject tempting options and instead select ones that produce greater long-term benefits. Although some apparent failures of self-control are, on closer inspection, reward maximizing, at least some self-control failures are clearly disadvantageous and non-strategic. The existence of poor self-control presents an important evolutionary puzzle because there is no obvious reason why good self-control should be more costly than poor self-control. After all, a rock is infinitely patient. I propose that self-control failures result from cases in which well-learned (and thus routinized) decision-making strategies yield suboptimal choices. These mappings persist in the decision-makers' repertoire because they result from learning processes that are adaptive in the broader context, either on the timescale of learning or of evolution. Self-control, then, is a form of cognitive control and the subjective feeling of effort likely reflects the true costs of cognitive control. Poor self-control, in this view, is ultimately a result of bounded optimality. This article is part of the theme issue 'Risk taking and impulsive behaviour: fundamental discoveries, theoretical perspectives and clinical implications.

Resource Signaling via Blood Glucose in Embodied Decision Making

Food, money, and time are exchangeable resources essential for survival and reproduction. Individuals live within finite budgets of these resources and make tradeoffs between money and time when making intertemporal choices between an immediate smaller reward and a delayed lager reward. In this paper, I examine signaling functions of blood glucose in regulating behaviors related to resource regulations beyond caloric metabolisms. These behavioral regulations include choices between energy expenditure and energy conservation, monetary intertemporal choices, and self-control in overcoming temptations. I begin by comparing potential embodied signals for resource forecasting and proactive decision making in terms of their pros and cons as a signal for regulating both metabolism and behavioral decision making and self-control. Based on this analysis, circulating glucose emerges as not only the designated fuel for brain metabolism but also a privileged resource forecasting signal for regulating immediate, short-term, and long-term behavioral adaptations to the resource budget of the decision maker. In the context of an on-going debate between the limited resource model and the motivation accounts of behavioral effects of blood glucose, I propose a dual functions (caloric provision and resource forecasting) and dual signaling (glucose taste and ingestion) hypothesis of circulating glucose in resource management, and provide behavioral and neurophysiological evidence of the separate effects of glucose taste to motivate effort for resource acquisition and glucose ingestion to promote resource conservation and future orientation. Accumulating evidence indicates that the body is able to detect fake signals of non-caloric sweeteners and react to such "caloric crisis" with an enhanced preference for immediate rewards over future rewards, revealing the wisdom of the body.

Mental Work Requires Physical Energy: Self-Control Is Neither Exception nor Exceptional

The brain’s reliance on glucose as a primary fuel source is well established, but psychological models of cognitive processing that take energy supply into account remain uncommon. One exception is research on self-control depletion, where debate continues over a limited-resource model. This model argues that a transient reduction in self-control after the exertion of prior self-control is caused by the depletion of brain glucose, and that self-control processes are special, perhaps unique, in this regard. This model has been argued to be physiologically implausible in several recent reviews. This paper attempts to correct some inaccuracies that have occurred during debate over the physiological plausibility of this model. We contend that not only is such limitation of cognition by constraints on glucose supply plausible, it is well established in the neuroscience literature across several cognitive domains. Conversely, we argue that there is no evidence that self-control is special in regard to its metabolic cost. Mental processes require physical energy, and the body is limited in its ability to supply the brain with sufficient energy to fuel mental processes. This article reviews current findings in brain metabolism and seeks to resolve the current conflict in the field regarding the physiological plausibility of the self-control glucose-depletion hypothesis.

A Simple, Principled Approach to Combining Evidence From Meta-Analysis and High-Quality Replications

Recent discussions of the influence of publication bias and questionable research practices on psychological science have increased researchers’ interest in both bias-correcting meta-analytic techniques and preregistered replication. Both approaches have their strengths: For example, meta-analyses can quantitatively characterize the full body of work done in the field of interest, and preregistered replications can be immune to bias. Both approaches also have clear weaknesses: Decisions about which meta-analytic estimates to interpret tend to be controversial, and replications can be discounted for failing to address important methodological heterogeneity. Using the experimental literature on ego depletion as a case study, we illustrate a principled approach to combining information from meta-analysis with information from subsequently conducted high-quality replications. This approach (a) compels researchers to explicate their beliefs in meta-analytic conclusions (and also, when controversy arises, to defend the basis for those beliefs), (b) encourages consideration of practical significance, and (c) facilitates the process of planning replications by specifying the sample sizes necessary to have a reasonable chance of changing the minds of other researchers.

Resource forecasting: Differential effects of glucose taste and ingestion on delay discounting and self-control

We tested a novel hypothesis that glucose taste acts as a signal for resource acquisition, motivating preference for immediate rewards while actual glucose ingestion prompts resource conservation, promoting future-orientated self-regulation. In Study 1, participants were engaged in a delay-discounting task and a grip-control task before and after a beverage intervention (glucose drink, water drink, or glucose mouth-rinse). Glucose ingestion decreased delay discounting, making larger-and-later rewards more attractive. In contrast, glucose rinse increased delay discounting. Water ingestion had none of the effects. In the grip-control task, only glucose ingestion improved the performance. Study 2 using fMRI revealed that glucose rinse and glucose ingestion resulted in distinct brain activational patterns. Compared to glucose rinse, glucose ingestion deactivated a few brain regions (e.g., the anterior cingulate gyrus and inferior frontal gyrus) that are previously shown to be more active when making more difficult intertemporal choices, suggesting that glucose ingestion eases the process of making intertemporal choice. In sum, our behavioral and neuroimaging findings together suggest a dual signaling role of glucose sensation and ingestion in regulating delay discounting and self-control.

High-disinhibition restrained eaters are disinhibited by self-regulatory depletion in the food-related inhibitory control

Restrained eating for weight control and loss is becoming highly prevalent in many affluent societies, while most of the restrained eaters are rather unsuccessful in the long term. According to the strength model of self-control, the disinhibition effect of restrained eaters may occur after the depletion of self-control resources. However, no work has examined the direct impact of self-control resources on inhibitory control ability of restrained eaters. This study investigated the influences of self-control resources on the food-related inhibitory control among high-restraint/low-disinhibition restrained eaters, high-restraint/high-disinhibition restrained eaters and unrestrained eaters using stop signal task. Results reveal that there's no difference of food-related inhibitory control between three groups when the self-control resources are non-depleted, while high-restraint/high-disinhibition restrained eaters showing a decrease of food-related inhibitory control after ego-depletion. This disinhibition effect only seems to occur in samples of restrained eaters with a high tendency toward overeating.

A Multilab Preregistered Replication of the Ego-Depletion Effect

Good self-control has been linked to adaptive outcomes such as better health, cohesive personal relationships, success in the workplace and at school, and less susceptibility to crime and addictions. In contrast, self-control failure is linked to maladaptive outcomes. Understanding the mechanisms by which self-control predicts behavior may assist in promoting better regulation and outcomes. A popular approach to understanding self-control is the strength or resource depletion model. Self-control is conceptualized as a limited resource that becomes depleted after a period of exertion resulting in self-control failure. The model has typically been tested using a sequential-task experimental paradigm, in which people completing an initial self-control task have reduced self-control capacity and poorer performance on a subsequent task, a state known as ego depletion Although a meta-analysis of ego-depletion experiments found a medium-sized effect, subsequent meta-analyses have questioned the size and existence of the effect and identified instances of possible bias. The analyses served as a catalyst for the current Registered Replication Report of the ego-depletion effect. Multiple laboratories (k = 23, total N = 2,141) conducted replications of a standardized ego-depletion protocol based on a sequential-task paradigm by Sripada et al. Meta-analysis of the studies revealed that the size of the ego-depletion effect was small with 95% confidence intervals (CIs) that encompassed zero (d = 0.04, 95% CI [-0.07, 0.15]. We discuss implications of the findings for the ego-depletion effect and the resource depletion model of self-control.

How to Make Nothing Out of Something: Analyses of the Impact of Study Sampling and Statistical Interpretation in Misleading Meta-Analytic Conclusions

The limited resource model states that self-control is governed by a relatively finite set of inner resources on which people draw when exerting willpower. Once self-control resources have been used up or depleted, they are less available for other self-control tasks, leading to a decrement in subsequent self-control success. The depletion effect has been studied for over 20 years, tested or extended in more than 600 studies, and supported in an independent meta-analysis (Hagger et al., 2010). Meta-analyses are supposed to reduce bias in literature reviews. Carter et al.’s (2015) meta-analysis, by contrast, included a series of questionable decisions involving sampling, methods, and data analysis. We provide quantitative analyses of key sampling issues: exclusion of many of the best depletion studies based on idiosyncratic criteria and the emphasis on mini meta-analyses with low statistical power as opposed to the overall depletion effect. We discuss two key methodological issues: failure to code for research quality, and the quantitative impact of weak studies by novice researchers. We discuss two key data analysis issues: questionable interpretation of the results of trim and fill and Funnel Plot Asymmetry test procedures, and the use and misinterpretation of the untested Precision Effect Test and Precision Effect Estimate with Standard Error (PEESE) procedures. Despite these serious problems, the Carter et al. (2015) meta-analysis results actually indicate that there is a real depletion effect – contrary to their title.

No Evidence of the Ego-Depletion Effect across Task Characteristics and Individual Differences: A Pre-Registered Study

Ego-depletion, a psychological phenomenon in which participants are less able to engage in self-control after prior exertion of self-control, has become widely popular in the scientific community as well as in the media. However, considerable debate exists among researchers as to the nature of the ego-depletion effect, and growing evidence suggests the effect may not be as strong or robust as the extant literature suggests. We examined the robustness of the ego-depletion effect and aimed to maximize the likelihood of detecting the effect by using one of the most widely used depletion tasks (video-viewing attention control task) and by considering task characteristics and individual differences that potentially moderate the effect. We also sought to make our research plan transparent by pre-registering our hypotheses, procedure, and planned analyses prior to data collection. Contrary to the ego-depletion hypothesis, participants in the depletion condition did not perform worse than control participants on the subsequent self-control task, even after considering moderator variables. These findings add to a growing body of evidence suggesting ego-depletion is not a reliable phenomenon, though more research is needed that uses large sample sizes, considers moderator variables, and pre-registers prior to data collection.

Carbohydrate ingestion but not mouth rinse maintains sustained attention when fasted

Carbohydrate (CHO) receptors in the mouth signal brain areas involved in cognitive tasks relying upon motivation and task persistence; however, the minimal CHO dose that improves mental activity is unclear.

PURPOSE

To determine if CHO (via ingestion or oral rinse) influences sustained attention without eliciting glycemic responses when in a fasted state.

METHODS

Study A: Six healthy adults completed five treatment trials, ingesting 0-6% CHO solutions to evaluate glycemic response. Peak blood glucose for 6% and 1.5% CHO was greater (p<0.05) than 0% and 0.4% CHO; thus, the low 0.4% CHO was evaluated further. Study B: Following an overnight fast, ten healthy adults completed three trials in a crossover design: 1) 400 ml 0.4% CHO ingested serially via 25 ml boluses, 2) 375 ml 0% CHO control (CON) ingested followed by one 25 ml 6% CHO isocaloric (1.5 g CHO) mouth rinse, and 3) CON ingest followed by CON rinse. Following treatments, a 20 min Continuous Performance Task (CPT) was performed to assess accuracy and precision.

RESULTS

Accuracy and precision were not different during the first 5 min of CPT. However, accuracy was maintained with CHO ingest (p=1.0) but decreased over 20 min (p<0.05) with both CHO and CON rinse treatments. Precision tended to decline over 20 min CPT with CON (p=0.06) and CHO rinse (p=0.05) but were maintained with CHO ingest (p=1.0). No differences in glycemic responses were observed between treatments.

CONCLUSIONS

Compared to mouth rinsing CON or CHO (1.5 g in 6% CHO), ingestion of an isocaloric low-CHO drink maintained sustained attention over a mentally fatiguing task and appears effective after fasting without eliciting a glycemic response.

Six Questions for the Resource Model of Control (and Some Answers)

The resource model of self-control casts self-control as a capacity that relies on some limited resource that exhausts with use. The model captured our imagination and brought much-needed attention on an important yet neglected psychological construct. Despite its success, basic issues with the model remain. Here, we ask six questions: (i) Does self-control really wane over time? (ii) Is ego depletion a form of mental fatigue? (iii) What is the resource that is depleted by ego depletion? (iv) How can changes in motivation, perception, and expectations replenish an exhausted resource? (v) Has the revised resource model unwittingly become a model about motivation? (vi) Do self-control exercises increase self-control? By providing some answers to these questions - including conducting a meta-analysis of the self-control training literature - we highlight how the resource model needs to be revised if not supplanted altogether.

Brief mindfulness induction reduces inattentional blindness

Prior research has linked mindfulness to improvements in attention, and suggested that the effects of mindfulness are particularly pronounced when individuals are cognitively depleted or stressed. Yet, no studies have tested whether mindfulness improves declarative awareness of unexpected stimuli in goal-directed tasks. Participants (N=794) were either depleted (or not) and subsequently underwent a brief mindfulness induction (or not). They then completed an inattentional blindness task during which an unexpected distractor appeared on the computer monitor. This task was used to assess declarative conscious awareness of the unexpected distractor's presence and the extent to which its perceptual properties were encoded. Mindfulness increased awareness of the unexpected distractor (i.e., reduced rates of inattentional blindness). Contrary to predictions, no mindfulness×depletion interaction emerged. Depletion however, increased perceptual encoding of the distractor. These results suggest that mindfulness may foster awareness of unexpected stimuli (i.e., reduce inattentional blindness).

Failure to replicate depletion of self-control

The limited resource or strength model of self-control posits that the use of self-regulatory resources leads to depletion and poorer performance on subsequent self-control tasks. We conducted four studies (two with community samples, two with young adult samples) utilizing a frequently used depletion procedure (crossing out letters protocol) and the two most frequently used dependent measures of self-control (handgrip perseverance and modified Stroop). In each study, participants completed a baseline self-control measure, a depletion or control task (randomized), and then the same measure of self-control a second time. There was no evidence for significant depletion effects in any of these four studies. The null results obtained in four attempts to replicate using strong methodological approaches may indicate that depletion has more limited effects than implied by prior publications. We encourage further efforts to replicate depletion (particularly among community samples) with full disclosure of positive and negative results.

Publication bias and the limited strength model of self-control: has the evidence for ego depletion been overestimated?

Few models of self-control have generated as much scientific interest as has the limited strength model. One of the entailments of this model, the depletion effect, is the expectation that acts of self-control will be less effective when they follow prior acts of self-control. Results from a previous meta-analysis concluded that the depletion effect is robust and medium in magnitude (d = 0.62). However, when we applied methods for estimating and correcting for small-study effects (such as publication bias) to the data from this previous meta-analysis effort, we found very strong signals of publication bias, along with an indication that the depletion effect is actually no different from zero. We conclude that until greater certainty about the size of the depletion effect can be established, circumspection about the existence of this phenomenon is warranted, and that rather than elaborating on the model, research efforts should focus on establishing whether the basic effect exists. We argue that the evidence for the depletion effect is a useful case study for illustrating the dangers of small-study effects as well as some of the possible tools for mitigating their influence in psychological science.

A Test of Learned Industriousness in the Physical Activity Domain

BACKGROUND

The Theory of Learned Industriousness states that durable individual differences in industriousness are due in part to differences in the extent to which individuals were rewarded for high effort at an earlier time. Individuals rewarded for high effort during training are thought to generalize greater persistence to subsequent tasks than those rewarded for low effort. This study tested whether rewarded physical and/or mental effort at different intensities generalized to greater persistence at a subsequent mental task.

METHODS

80 inactive 18-25 year-olds were randomized into four groups: Low Mental Effort, High Mental Effort, Low Physical Effort, and High Physical Effort. Each completed group-specific effort training and a mental persistence task at baseline and posttest.

RESULTS

Factorial analysis of covariance revealed a significant domain x effort interaction on persistence (F[1,75]=4.93, p=.029). High Mental Effort and Low Mental Effort groups demonstrated similar gains in persistence (d=-0.08, p>.05) and points earned (d=0.11, p>.05) following effort training. High Physical Effort and Low Physical Effort diverged on persistence (d=-0.49, p=.004) but not points earned (d =-0.12, p>.05).

CONCLUSIONS

Findings suggest either that training and test stimuli were too dissimilar to cue effects of associative learning in physical effort groups, or that effects were present but overpowered by the affective and neurocognitive consequences of an acute bout of intense aerobic physical activity. Findings do not support the Theory of Learned Industriousness nor generalization of effort across physical and mental domains.