Mental fatigue measurement using eye metrics: A systematic literature review

Acoustic scene complexity affects motion behavior during speech perception in audio-visual multi-talker virtual environments

In real-world listening situations, individuals typically utilize head and eye movements to receive and enhance sensory information while exploring acoustic scenes. However, the specific patterns of such movements have not yet been fully characterized. Here, we studied how movement behavior is influenced by scene complexity, varied in terms of reverberation and the number of concurrent talkers. Thirteen normal-hearing participants engaged in a speech comprehension and localization task, requiring them to indicate the spatial location of a spoken story in the presence of other stories in virtual audio-visual scenes. We observed delayed initial head movements when more simultaneous talkers were present in the scene. Both reverberation and a higher number of talkers extended the search period, increased the number of fixated source locations, and resulted in more gaze jumps. The period preceding the participants' responses was prolonged when more concurrent talkers were present, and listeners continued to move their eyes in the proximity of the target talker. In scenes with more reverberation, the final head position when making the decision was farther away from the target. These findings demonstrate that the complexity of the acoustic scene influences listener behavior during speech comprehension and localization in audio-visual scenes.

Oculometric biomarkers of visuomotor deficits in clinically asymptomatic patients with systemic lupus erythematosus undergoing long-term hydroxychloroquine treatment

Introduction

This study examines a set of oculomotor measurements, or "oculometric" biomarkers, as potential early indicators of visual and visuomotor deficits due to retinal toxicity in asymptomatic Systemic Lupus Erythematosus (SLE) patients on long-term hydroxychloroquine (HCQ) treatment. The aim is to identify subclinical functional impairments that are otherwise undetectable by standard clinical tests and to link them to structural retinal changes.

Methods

We measured oculomotor responses in a cohort of SLE patients on chronic HCQ therapy using a previously established behavioral task and analysis technique. We also examined the relationship between oculometrics, OCT measures of retinal thickness, and standard clinical perimetry measures of visual function in our patient group using Bivariate Pearson Correlation and a Linear Mixed-Effects Model (LMM).

Results

Significant visual and visuomotor deficits were found in 12 asymptomatic SLE patients on long-term HCQ therapy compared to a cohort of 17 age-matched healthy controls. Notably, six oculometrics were significantly different. The median initial pursuit acceleration was 22%, steady-state pursuit gain 16%, proportion smooth 7%, and target speed responsiveness 31% lower, while catch-up saccade amplitude was 46% and fixation error 46% larger. Excluding the two patients with diagnosed mild toxicity, four oculometrics, all but fixation error and proportion smooth, remained significantly impaired compared to controls. Across our population of 12 patients (24 retinae), we found that pursuit latency, initial acceleration, steady-state gain, and fixation error were linearly related to retinal thickness even when age was accounted for, while standard measures of clinical function (Mean Deviation and Pattern Standard Deviation) were not.

Discussion

Our data show that specific oculometrics are sensitive early biomarkers of functional deficits in SLE patients on HCQ that could be harnessed to assist in the early detection of HCQ-induced retinal toxicity and other visual pathologies, potentially providing early diagnostic value beyond standard visual field and OCT evaluations.

State-Dependent tACS Effects Reveal the Potential Causal Role of Prestimulus Alpha Traveling Waves in Visual Contrast Detection

The intricate relationship between prestimulus alpha oscillations and visual contrast detection variability has been the focus of numerous studies. However, the causal impact of prestimulus alpha traveling waves on visual contrast detection remains largely unexplored. In our research, we sought to discern the causal link between prestimulus alpha traveling waves and visual contrast detection across different levels of mental fatigue. Using electroencephalography alongside a visual detection task with 30 healthy adults (13 females; 17 males), we identified a robust negative correlation between prestimulus alpha forward traveling waves (FTWs) and visual contrast threshold (VCT). Inspired by this correlation, we utilized 45/-45° phase-shifted transcranial alternating current stimulation (tACS) in a sham-controlled, double-blind, within-subject experiment with 33 healthy adults (23 females; 10 males) to directly modulate these alpha traveling waves. After the application of 45° phase-shifted tACS, we observed a substantial decrease in FTW and an increase in backward traveling waves, along with a concurrent increase in VCT, compared with the sham condition. These changes were particularly pronounced under a low fatigue state. The findings of state-dependent tACS effects reveal the potential causal role of prestimulus alpha traveling waves in visual contrast detection. Moreover, our study highlights the potential of 45/-45° phase-shifted tACS in cognitive modulation and therapeutic applications.

Acute combined effects of concurrent physical activities on autonomic nervous activation during cognitive tasks

Backgrounds: The validity of heart rate variability (HRV) has been substantiated in mental workload assessments. However, cognitive tasks often coincide with physical exertion in practical mental work, but their synergic effects on HRV remains insufficiently established. The study aims were to investigate the combined effects of cognitive and physical load on autonomic nerve functions. Methods: Thirty-five healthy male subjects (aged 23.5 ± 3.3 years) were eligible and enrolled in the study. The subjects engaged in n-back cognitive tasks (1-back, 2-back, and 3-back) under three distinct physical conditions, involving isotonic contraction of the left upper limb with loads of 0 kg, 3 kg, and 5 kg. Electrocardiogram signals and cognitive task performance were recorded throughout the tasks, and post-task assessment of subjective experiences were conducted using the NASA-TLX scale. Results: The execution of n-back tasks resulted in enhanced perceptions of task-load feelings and increased reaction times among subjects, accompanied by a decline in the accuracy rate (p < 0.05). These effects were synchronously intensified by the imposition of physical load. Comparative analysis with a no-physical-load scenario revealed significant alterations in the HRV of the subjects during the cognitive task under moderate and high physical conditions. The main features were a decreased power of the high frequency component (p < 0.05) and an increased low frequency component (p < 0.05), signifying an elevation in sympathetic activity. This physiological response manifested similarly at both moderate and high physical levels. In addition, a discernible linear correlation was observed between HRV and task-load feelings, as well as task performance under the influence of physical load (p < 0.05). Conclusion: HRV can serve as a viable indicator for assessing mental workload in the context of physical activities, making it suitable for real-world mental work scenarios.

Prolonged cognitive effort impairs inhibitory control and causes significant mental fatigue after an endurance session with an auditive distractor in professional soccer players

BACKGROUND

Throughout official soccer matches, the presence of cheer by the crowd could be considered a critical auditive distraction that could further impair the cognitive interference control system, multiple object tracking (MOT) skill, heart rate variability (HRV), and increase mental fatigue. As the resource is not immediately replenished, the impairment of the cognitive interference control system may be delayed following a soccer game. Then, evaluating the recovery time course of the cognitive interference control system, MOT skill, HRV, and mental fatigue after prolonged tasks combining physical, endurance, and cognitive effort are essential.

PURPOSE

We aimed to analyze the acute effect of cognitive effort and auditive distractor with 24-h follow-up throughout a prolonged endurance session on inhibitory control, subjective mental fatigue, MOT skill, and HRV in professional soccer players.

METHODS

Twenty professional male soccer players were recruited (23.56 ± 3.8 years, 78.1 ± 6.9 kg, 1.77 ± 0.06 m, and 12.5 ± 5.3% body fat). The sessions were performed in a randomized and counterbalanced crossover design, divided into four experimental conditions: endurance, endurance + MOT, endurance + MOT + AD, and endurance + AD. The soccer players completed the incongruent Stroop task utilizing an eye-tracker to assess cognitive effort. MOT task, subjective mental fatigue, and HRV were evaluated before the endurance training (60%Δ of maximal aerobic velocity during 40-min) and after 30-min and 24-h of recovery. These sessions were designed to investigate the acute effect of prolonged cognitive effort (repeated MOT throughout the endurance task) and AD (constant crowd noise and coach's voice each 15-40 s, totalizing = 80 voices) on inhibitory control, MOT skills, HRV, and subjective mental fatigue after a fixed endurance training session.

RESULTS

There was no condition × time interaction for accuracy of inhibitory control (p > 0.05, ηp2 = 0.001). There was a significant condition × time interaction for inhibitory control response time (p < 0.05, ηp2 = 0.16). A higher response time of inhibitory control was found for the endurance + MOT + AD and endurance + MOT experimental sessions (p < 0.05). There was a significant condition × time interaction for subjective mental fatigue (p < 0.05, ηp2 = 0.46). A higher subjective mental fatigue was found for the endurance + MOT + AD and endurance + MOT experimental sessions (p < 0.05). There was no condition × time interaction for HRV (p > 0.05, ηp2 = 0.02).

CONCLUSION

We concluded that cognitive effort throughout a prolonged endurance session impaired inhibitory control and increased mental fatigue without promoting greater MOT skill and HRV changes in professional soccer players.

The impact of videogames on the mood of amateur youth players during consecutive games

Introduction

Esports have experienced tremendous growth in recent years. In the scientific field, previous research has shown the determining role of psychology in competitive performance, but little is known about the factors that may be more determinant. In addition, in the amateur field, where fun and enjoyment are the most important factors, it has been observed that players can see their psychological state altered due to different factors, but it is not known if the outcome of the game (win or lose) can be influential. For this reason, the aim of the present investigation was to analyze changes in players' mood between three consecutive games as a function of the outcome of each game.

Methods

A total of 14 amateur players participated in the research, all of them with previous experience and being regular League of Legends players. The participants completed the POMS questionnaire before the start of each game and the outcome of each game was recorded at the end.

Results

The results showed that no significant pre-game differences were found in any of the games, regardless of winning or losing. Significant differences were found in the pre-game mood between the first and second game, according to the outcome of the first game, and between the second and third game, according to the outcome of the second game. Between the first and second games, there was a significant increase in depression (p = 0.038) and anger (p = 0.003) when the first game was lost; and between the second and third games, there was a decrease in tension (p = 0.003) and anger (p = 0.022) when the second game was won. In addition, it should be noted that fatigue increased significantly after each game, regardless of the outcome, and with respect to the change in mood, this was more noticeable when the first game was lost and the second was won, as significant changes were observed in tension (p = 0.028), depression (p = 0.030) and anger (p = 0.006).

Conclusion

Pre-match mood does not influence post-match performance, but mood changes do occur between successive matches depending on the outcome of the match.

Effect of brain endurance training on maximal oxygen uptake, time-to-exhaustion, and inhibitory control in runners

We aimed to analyze the effect of brain endurance training on maximum oxygen consumption (VO2máx ), time-to-exhaustion, and inhibitory control in amateur trained runners. We employed a mixed experimental design, with the group as the between-participant factor and time as the within-participant factor. 45 participants attended 36 training sessions over 12 weeks. The cognitive training group (CT) performed the Stroop word-color task [trials of each type (congruent, incongruent, and neutral) were randomly presented during each training session], the endurance training group (ET) participated in a running training program (intensity was 60%Δ of maximal aerobic velocity and performed on a motor-driven treadmill), and the brain endurance training group (BET) make cognitive and endurance training simultaneously over 12 weeks. The total time of each session (i.e., 20-40 min) was identical in the experimental groups. VO2máx , time-to-exhaustion, and inhibitory control tests were measured before (baseline) and after (post-experiment) the 12-week intervention. A significant effect of interaction (group × time) for VO2máx (p < 0.05) was found. A post-hoc test showed an increase in VO2máx from baseline to post-experiment only for ET (Δ% = 2.98) and BET (Δ% = 3.78) groups (p < 0.05). Also, the analyses showed a significant interaction (group × time) for time-to-exhaustion (p < 0.05), and a post-hoc test revealed an improvement in time-to-exhaustion for ET (Δ% = 8.81) and BET (Δ% = 11.01) (p < 0.05). No group × time interaction was found for accuracy and response time in the inhibitory control task (p > 0.05). The results conclude that BET was not superior to ET for improving VO2máx and time-to-exhaustion. Also, the findings conclude that BET improved inhibitory control similar to CT.

Psychophysiological models of hypovigilance detection: A scoping review

Hypovigilance represents a major contributor to accidents. In operational contexts, the burden of monitoring/managing vigilance often rests on operators. Recent advances in sensing technologies allow for the development of psychophysiology-based (hypo)vigilance prediction models. Still, these models remain scarcely applied to operational situations and need better understanding. The current scoping review provides a state of knowledge regarding psychophysiological models of hypovigilance detection. Records evaluating vigilance measuring tools with gold standard comparisons and hypovigilance prediction performances were extracted from MEDLINE, PsychInfo, and Inspec. Exclusion criteria comprised aspects related to language, non-empirical papers, and sleep studies. The Quality Assessment tool for Diagnostic Accuracy Studies (QUADAS) and the Prediction model Risk Of Bias ASsessment Tool (PROBAST) were used for bias evaluation. Twenty-one records were reviewed. They were mainly characterized by participant selection and analysis biases. Papers predominantly focused on driving and employed several common psychophysiological techniques. Yet, prediction methods and gold standards varied widely. Overall, we outline the main strategies used to assess hypovigilance, their principal limitations, and we discuss applications of these models.

Head-to-head opponent mitigates mental fatigue effects during a 20-km time trial in well-trained cyclists

We aimed to analyze the effect of a head-to-head virtual race on 20-km time trial performance in well-trained mentally fatigued cyclists. A total of 24 male professional cyclists participated in the present study, which was conducted in a within-factors design [four experimental conditions × four times (throughout 20-km time trial cycling)]. An avatar representing the participant on the racecourse was visible during the time trials. Then, a second virtual avatar representing the opponent was projected onto the screen in the mental fatigue head-to-head and control head-to-head experimental conditions. Measurements [rating of perceived exertion, heart rate, and eye-tracking measures (i.e., pupil diameter)] were performed every 5-km throughout the 20-km time trial. As a result, impaired total time, power output, and cadence throughout the 20-km cycling time trial were found for mental fatigue compared to mental fatigue head-to-head, control head-to-head, and control conditions (p < 0.05). Also, impaired 20-km time trial performance (total time, power output, and cadence) was found for mental fatigue head-to-head compared to control head-to-head (p < 0.05). Moreover, lower RPE was found for the control and control head-to-head conditions than mental fatigue head-to-head and mental fatigue experimental conditions (p < 0.05). Higher pupil diameter was also found for mental fatigue head-to-head, control head-to-head, and control than the mental fatigue experimental condition (p < 0.05). In summary, the overall performance throughout the 20-km cycling time trial was improved by the presence of a virtual opponent for the mentally fatigued cyclists.

Psychological states affecting initial pupil size changes after olfactory stimulation in healthy participants

Odor perception affects physiological and psychological states. Pupillary light reflex (PLR) parameters can be affected by olfactory stimulation and psychological states, although it remains unclear whether the olfactory stimulation-induced psychological changes can associate with PLR parameter changes. This study aimed to investigate effects of olfactory stimulation-induced psychological changes on PLR parameter changes with repeated measurements. We collected data on six mood subscales of the profile of mood states, and on five PLR parameter measurements from 28 healthy participants. Participants underwent a 10-min olfactory stimulation on different days with six odorants available with the T&T olfactometer. As obtained data were clustered, we used linear mixed-effects models for statistical analyses. The olfactory stimulation using the no-odor liquid did not affect mood states and the initial pupil size (INIT). The sweat odorant worsened all mood subscales including fatigue-inertia (Fatigue)/Vigor-Activity (Vigor), and decreased INIT compared to the no-odor liquid. When comparing INIT responses related to changes in mood subscales between the no-odor liquid and the sweat odorant, worsened states of Fatigue/Vigor were associated with decreased INIT in the sweat odorant. Fatigue/Vigor can be used as mental fatigue indicators. Thus, mental fatigue can be associated with decreased INIT in the olfactory stimulation.

Beyond the symptom: the biology of fatigue

A workshop titled "Beyond the Symptom: The Biology of Fatigue" was held virtually September 27-28, 2021. It was jointly organized by the Sleep Research Society and the Neurobiology of Fatigue Working Group of the NIH Blueprint Neuroscience Research Program. For access to the presentations and video recordings, see: https://neuroscienceblueprint.nih.gov/about/event/beyond-symptom-biology-fatigue. The goals of this workshop were to bring together clinicians and scientists who use a variety of research approaches to understand fatigue in multiple conditions and to identify key gaps in our understanding of the biology of fatigue. This workshop summary distills key issues discussed in this workshop and provides a list of promising directions for future research on this topic. We do not attempt to provide a comprehensive review of the state of our understanding of fatigue, nor to provide a comprehensive reprise of the many excellent presentations. Rather, our goal is to highlight key advances and to focus on questions and future approaches to answering them.

Understanding mental fatigue and its detection: a comparative analysis of assessments and tools

Mental fatigue has shown to be one of the root causes of decreased productivity and overall cognitive performance, by decreasing an individual's ability to inhibit responses, process information and concentrate. The effects of mental fatigue have led to occupational errors and motorway accidents. Early detection of mental fatigue can prevent the escalation of symptoms that may lead to chronic fatigue syndrome and other disorders. To date, in clinical settings, the assessment of mental fatigue and stress is done through self-reported questionnaires. The validity of these questionnaires is questionable, as they are highly subjective measurement tools and are not immune to response biases. This review examines the wider presence of mental fatigue in the general population and critically compares its various detection techniques (i.e., self-reporting questionnaires, heart rate variability, salivary cortisol levels, electroencephalogram, and saccadic eye movements). The ability of these detection tools to assess inhibition responses (which are sensitive enough to be manifested in a fatigue state) is specifically evaluated for a reliable marker in identifying mentally fatigued individuals. In laboratory settings, antisaccade tasks have been long used to assess inhibitory control and this technique can potentially serve as the most promising assessment tool to objectively detect mental fatigue. However, more studies need to be conducted in the future to validate and correlate this assessment with other existing measures of mental fatigue detection. This review is intended for, but not limited to, mental health professionals, digital health scientists, vision researchers, and behavioral scientists.

Repeated stroboscopic vision training improves anticipation skill without changing perceptual-cognitive skills in soccer players

In this study we aimed to analyze the repeated effect of stroboscopic vision training on perceptual-cognitive skills in soccer players. A total of 28 male soccer players participated in this experimental and randomized study with parallel groups. The soccer players were pair-matched according to perceptual-cognitive skills and randomized into two groups: Stroboscopic vision training and Control. Multiple object tracking, anticipation, and decision-making skills were measured before and after the 8-week intervention. An increase in multiple object tracking (p < 0.05) and decision-making skills (p < 0.05) from baseline to post-experiment was found in both groups without main group effect (p > 0.05). The findings showed an increase in anticipation skill from baseline to post-experiment in both groups (p < 0.05), with higher anticipation skill for the stroboscopic group than in the control group post-experiment (p < 0.05). Thus, we conclude that repeated stroboscopic vision training could improve anticipation skill in soccer athletes.

Eye movement characteristics are not significantly influenced by psychiatric comorbidities in people with visual snow syndrome

Visual snow syndrome (VSS) is a neurological disorder primarily affecting the processing of visual information. Using ocular motor (OM) tasks, we previously demonstrated that participants with VSS exhibit altered saccade profiles consistent with visual attention impairments. We subsequently proposed that OM assessments may provide an objective measure of dysfunction in these individuals. However, VSS participants also frequently report significant psychiatric symptoms. Given that that these symptoms have been shown previously to influence performance on OM tasks, the objective of this study was to investigate whether psychiatric symptoms (specifically: depression, anxiety, fatigue, sleep difficulties, and depersonalization) influence the OM metrics found to differ in VSS. Sixty-one VSS participants completed a battery of four OM tasks and a series of online questionnaires assessing psychiatric symptomology. We revealed no significant relationship between psychiatric symptoms and OM metrics on any of the tasks, demonstrating that in participants with VSS, differences in OM behaviour are a feature of the disorder. This supports the utility of OM assessment in characterising deficit in VSS, whether supporting a diagnosis or monitoring future treatment efficacy.

A CNN-Based Wearable System for Driver Drowsiness Detection

Drowsiness poses a serious challenge to road safety and various in-cabin sensing technologies have been experimented with to monitor driver alertness. Cameras offer a convenient means for contactless sensing, but they may violate user privacy and require complex algorithms to accommodate user (e.g., sunglasses) and environmental (e.g., lighting conditions) constraints. This paper presents a lightweight convolution neural network that measures eye closure based on eye images captured by a wearable glass prototype, which features a hot mirror-based design that allows the camera to be installed on the glass temples. The experimental results showed that the wearable glass prototype, with the neural network in its core, was highly effective in detecting eye blinks. The blink rate derived from the glass output was highly consistent with an industrial gold standard EyeLink eye-tracker. As eye blink characteristics are sensitive measures of driver drowsiness, the glass prototype and the lightweight neural network presented in this paper would provide a computationally efficient yet viable solution for real-world applications.

Recommendation of using both initial pupil size and constriction latency in pupillary light reflex as objective indicators reflecting subacute pain-related mental fatigue

A previous study examining clinical subacute pain models under different methodological conditions showed that pain-induced mental fatigue can be associated with decreased initial pupil size (INIT)/shortened constriction latency (LAT) in the pupillary light reflex (PLR). We aimed to investigate the potential of INIT/LAT as objective indicators reflecting mental fatigue under the same methodological conditions. We recruited 118 patients planning to undergo three types of representative otolaryngological head and neck surgery procedures. We used the numerical rating scale (NRS) to assess subjective pain intensity and two mental fatigue-related mood categories of the Profile of Mood States, as well as INIT and LAT measurements (1) in the afternoon one day before surgery (pre1-surgery), (2) in the morning of the day of surgery (pre2-surgery), and (3) in the morning of the day following surgery (post-surgery). We assessed time point-dependent changes using one- or two-way analysis of variance, as well as responses of PLR parameters to mental fatigue using linear mixed-effects models (LMMs). As a result, NRS scores, the two mood categories, as well as LAT and INIT, showed significant time point-dependent changes. In post-hoc analyses, only INIT showed significant changes between the two pre-surgery time points. Thus, INIT values fluctuated even under pain-free conditions due to differences in the time of the day. LMMs demonstrated decreased INIT/shortened LAT related to mental fatigue. All surgical groups showed similar associations between mental fatigue and INIT/LAT findings. As each parameter has advantages and disadvantages, it is recommended to use both INIT and LAT as the indicators.

Clear Aligners and Smart Eye Tracking Technology as a New Communication Strategy between Ethical and Legal Issues

Smart eye-tracking technology (SEET) that determines visual attention using smartphones can be used to determine the aesthetic perception of different types of clear aligners. Its value as a communication and comprehension tool, in addition to the ethical and legal concerns which it entails, can be assessed. One hundred subjects (50 F, 50 M; age range 15-70) were equally distributed in non-orthodontic (A) and orthodontic (B) groups. A smartphone-based SEET app assessed their knowledge of and opinions on aligners. Subjects evaluated images of smiles not wearing aligners, with/without attachments and with straight/scalloped gingival margins, as a guided calibration step which formed the image control group. Subsequently, the subjects rated the same smiles, this time wearing aligners (experimental images group). Questionnaire data and average values for each group of patients, and images relating to fixation times and overall star scores, were analyzed using these tests: chi-square, t-test, Mann-Whitney U, Spearman's rho, and Wilcoxon (p < 0.05). One-way ANOVA and related post-hoc tests were also applied. Orthodontic patients were found to be better informed than non-orthodontic patients. Aesthetic perception could be swayed by several factors. Attachments scored lower in aesthetic evaluation. Lips distracted attention from attachments and improved evaluations. Attachment-free aligners were better rated overall. A more thorough understanding as to the opinions, expectations and aesthetic perception of aligners can improve communication with patients. Mobile SEET is remarkably promising, although it does require a careful medicolegal risk-benefit assessments for responsible and professional use.

Fatigue and Human Performance: An Updated Framework

Fatigue has been defined differently in the literature depending on the field of research. The inconsistent use of the term fatigue complicated scientific communication, thereby limiting progress towards a more in-depth understanding of the phenomenon. Therefore, Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) proposed a fatigue framework that distinguishes between trait fatigue (i.e., fatigue experienced by an individual over a longer period of time) and motor or cognitive task-induced state fatigue (i.e., self-reported disabling symptom derived from the two interdependent attributes performance fatigability and perceived fatigability). Thereby, performance fatigability describes a decrease in an objective performance measure, while perceived fatigability refers to the sensations that regulate the integrity of the performer. Although this framework served as a good starting point to unravel the psychophysiology of fatigue, several important aspects were not included and the interdependence of the mechanisms driving performance fatigability and perceived fatigability were not comprehensively discussed. Therefore, the present narrative review aimed to (1) update the fatigue framework suggested by Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) pertaining the taxonomy (i.e., cognitive performance fatigue and perceived cognitive fatigue were added) and important determinants that were not considered previously (e.g., effort perception, affective valence, self-regulation), (2) discuss the mechanisms underlying performance fatigue and perceived fatigue in response to motor and cognitive tasks as well as their interdependence, and (3) provide recommendations for future research on these interactions. We propose to define motor or cognitive task-induced state fatigue as a psychophysiological condition characterized by a decrease in motor or cognitive performance (i.e., motor or cognitive performance fatigue, respectively) and/or an increased perception of fatigue (i.e., perceived motor or cognitive fatigue). These dimensions are interdependent, hinge on different determinants, and depend on body homeostasis (e.g., wakefulness, core temperature) as well as several modulating factors (e.g., age, sex, diseases, characteristics of the motor or cognitive task). Consequently, there is no single factor primarily determining performance fatigue and perceived fatigue in response to motor or cognitive tasks. Instead, the relative weight of each determinant and their interaction are modulated by several factors.

Previous Mental Load and Incentives Influence Anticipatory Arousal as Indexed by the Baseline Pupil Diameter in a Speech-in-Noise Task

Listening effort and fatigue are common experiences when conversing in noisy environments. Much research has investigated listening effort in relation to listening demand using the speech-in-noise paradigm. Recent conceptualizations of listening effort postulate that mental fatigue should result in decreased arousal and a reluctance to invest further effort, particularly when the effort is not worthwhile. The aim of the study was to investigate the influence of fatigue on listening effort, in interaction with listening demands and motivation. To induce fatigue 30 adults with normal hearing completed a 40-minute long speech-in-noise task ("load sequence"). Pre- and post-load sequence listening effort was probed in easy and hard listening demands (individually adjusted signal-to-noise ratios); with high and low motivation (manipulated with monetary incentives). Subjective effort, estimated performance, and tendency to quit listening were collected using rating scales. Baseline pupil diameter and mean pupil dilation were recorded as indices of anticipatory arousal and objective effort. Self-reported effort and mean pupil dilation were overall larger during hard SNR as compared to easy SNR. Baseline pupil diameter declined from pre- to post-load sequence, suggesting an overall decrease in arousal. Monetary incentives had no influence on the baseline pupil diameter for the easy SNR condition, but for the hard SNR condition larger incentives led to larger baseline pupil diameter. These results suggest that anticipatory arousal may be influenced by fatigue and motivation effects. Models of listening effort should account for the independent influence of motivation and previous load on anticipatory arousal and effort in distinct parameters.

Neural mechanisms underlying state mental fatigue: a systematic review and activation likelihood estimation meta-analysis

Sustained performance of cognitive tasks could lead to the development of state mental fatigue characterized by subjective sensation of mental weariness and decrease in cognitive performance. In addition to the occupational hazards associated with mental fatigue, it can also affect physical performance reducing endurance, balance, and sport-specific technical skills. Similarly, mental fatigue is a common symptom in certain chronic health conditions such as multiple sclerosis affecting quality of life of the patients. Despite its widely acknowledged negative impact, the neural mechanisms underlining this phenomenon are still not fully understood. We conducted a systematic review and activation likelihood estimation (ALE) meta-analysis of functional neuroimaging studies investigating the effect of mental fatigue due to time-on-task (TOT) on brain activity to elucidate the possible underlying mechanisms. Studies were included if they examined change in brain activity induced by experimental mental fatigue (TOT effect) or investigated the relationship between brain activity and subjective mental fatigue due to TOT. A total of 33 studies met the review's inclusion criteria, 13 of which were included in meta-analyses. Results of the meta-analyses revealed a decrease in activity with TOT in brain areas that constitute the cognitive control network. Additionally, an increased activity with TOT, as well as negative relationship with subjective mental fatigue was found in parts of the default mode network of the brain. The changes in cognitive control and the default mode networks of the brain due to state mental fatigue observed in this study were discussed in relation to the existing theories of mental fatigue.

Decreased initial pupil size and shortened constriction latency due to negative mood states and mental fatigue in clinical subacute pain models

Previous clinical studies on pupillary light reflex parameters showed shortened constriction latency (LAT) and decreased initial pupil size (INIT) due to increased numeric rating scale (NRS) scores, reflecting subjective pain intensity, in subacute pain models. As noxious stimulation causes pupil dilation, decreased INIT (pupil constriction) was an unexpected finding. Pain-related negative moods and mental fatigue might have caused this finding. We aimed to investigate how psychological states affect LAT/INIT in two subacute pain models. For psychological assessment, we used the Profile of Mood States (POMS) and calculated the total mood disturbance (TMD) score using six mood categories. We collected data on NRS scores, POMS-related scores, LAT, and INIT through a longitudinal study. Using linear mixed-effects models, we evaluated the association of TMD scores with NRS scores, LAT, and INIT. Furthermore, we performed subanalyses targeting two mood categories that represent mental fatigue: Fatigue-Inertia (Fatigue) and Vigor-Activity (Vigor). We investigated whether obtained results can be identical in both models. In total, 141 patients were enrolled. Increased NRS scores were associated with increased TMD/Fatigue scores and decreased Vigor scores, being associated with shortened LAT/decreased INIT in both models. Score changes in NRS, TMD, Fatigue, and Vigor indicated that increased subjective pain intensity can be associated with negative mood states, especially mental fatigue. This study revealed that negative moods and mental fatigue induced by acute pain can be associated with shortened LAT/decreased INIT in both models, indicating clinical potential of LAT/INIT as objective indicators reflecting the psychological states for pain assessment.

Brain Stimulation Over the Motion-Sensitive Midtemporal Area Reduces Deleterious Effects of Mental Fatigue on Perceptual-Cognitive Skills in Basketball Players

The objective of this study was to analyze the effect of anodal transcranial direct current stimulation (a-tDCS) over the motion-sensitive midtemporal area on perceptual-cognitive skills (visuomotor and basketball decision-making skills) in mentally fatigued basketball players. A total of 20 male basketball players were recruited. This was a randomized, double-blinded, and counterbalanced crossover study with two experimental conditions: a-tDCS and Sham. The participants completed the basketball decision-making task and visuomotor skill after performing a 60-min sport-based videogame task with anodal (i.e., a-tDCS) or placebo (Sham) stimulation over the motion-sensitive middle temporal area. Worse response time was observed in visuomotor skill for Sham than a-tDCS postexperiment (p < .05). There was no main condition effect for accuracy of visuomotor skill (p > .05). There was more impairment in accuracy and response time in basketball decision-making skills for the Sham condition than a-tDCS (p < .05). Notably, a-tDCS over the motion-sensitive middle temporal area removed the negative effects of mental fatigue on perceptual-cognitive skills.

Publication guidelines and recommendations for pupillary measurement in psychophysiological studies

A variety of psychological and physical phenomena elicit variations in the diameter of pupil of the eye. Changes in pupil size are mediated by the relative activation of the sphincter pupillae muscle (decrease pupil diameter) and the dilator pupillae muscle (increase pupil diameter), innervated by the parasympathetic and sympathetic branches, respectively, of the autonomic nervous system. The current guidelines are intended to inform and guide psychophysiological research involving pupil measurement by (1) summarizing important aspects concerning the physiology of the pupil, (2) providing methodological and data-analytic guidelines and recommendations, and (3) briefly reviewing psychological phenomena that modulate pupillary reactivity. Because of the increased ease and tractability of pupil measurement, the goal of these guidelines is to promote accurate recording, analysis, and reporting of pupillary data in psychophysiological research.

Let Complexity Bring Clarity: A Multidimensional Assessment of Cognitive Load Using Physiological Measures

The effects of cognitive load on driver behavior and traffic safety are unclear and in need of further investigation. Reliable measures of cognitive load for use in research and, subsequently, in the development and implementation of driver monitoring systems are therefore sought. Physiological measures are of interest since they can provide continuous recordings of driver state. Currently, however, a few issues related to their use in this context are not usually taken into consideration, despite being well-known. First, cognitive load is a multidimensional construct consisting of many mental responses (cognitive load components) to added task demand. Yet, researchers treat it as unidimensional. Second, cognitive load does not occur in isolation; rather, it is part of a complex response to task demands in a specific operational setting. Third, physiological measures typically correlate with more than one mental state, limiting the inferences that can be made from them individually. We suggest that acknowledging these issues and studying multiple mental responses using multiple physiological measures and independent variables will lead to greatly improved measurability of cognitive load. To demonstrate the potential of this approach, we used data from a driving simulator study in which a number of physiological measures (heart rate, heart rate variability, breathing rate, skin conductance, pupil diameter, eye blink rate, eye blink duration, EEG alpha power, and EEG theta power) were analyzed. Participants performed a cognitively loading n-back task at two levels of difficulty while driving through three different traffic scenarios, each repeated four times. Cognitive load components and other coinciding mental responses were assessed by considering response patterns of multiple physiological measures in relation to multiple independent variables. With this approach, the construct validity of cognitive load is improved, which is important for interpreting results accurately. Also, the use of multiple measures and independent variables makes the measurements (when analyzed jointly) more diagnostic-that is, better able to distinguish between different cognitive load components. This in turn improves the overall external validity. With more detailed, diagnostic, and valid measures of cognitive load, the effects of cognitive load on traffic safety can be better understood, and hence possibly mitigated.

Mental fatigue increases across a 16-week pre-season in elite female athletes

OBJECTIVES

To examine potential changes in mental and physical fatigue across an elite netball pre-season training phase and relationships between mental fatigue, physical fatigue, salivary cortisol (sCort) and alpha-amylase (sAA).

DESIGN

Observational with repeated measures.

METHODS

Across a 16-week pre-season, 10 elite female netballers (25.3 ± 3.7y) rated their physical fatigue, mental fatigue and readiness to perform on 100-mm visual analogue scales, and provided salivary samples for sCort and sAA analyses.

RESULTS

Linear mixed model analyses revealed elevated (p < 0.05) ratings of mental fatigue for weeks 12, 14 and 15 v 1; 12, 14 and 15 v 4 and 14 v 7. Higher (p < 0.05) ratings of physical fatigue were reported on weeks 6, 10, 11 and 12-16 compared to week 4; and 10 and 13 compared to week 7. Moderate and large ES differences were found between multiple weeks. Mental and physical fatigue demonstrated a shared variance of 14.3% (r = 0.38, p < 0.001) and an inverse relationship was observed between mental fatigue and readiness to perform (r = -0.50; p < 0.001). Changes in sCort nor sAA were not related to changes in mental or physical fatigue.

CONCLUSIONS

Mental fatigue fluctuated across the 16-week pre-season phase with elevated ratings observed in the later weeks. Whilst value remains in identifying subjective tools to assess mental fatigue; salivary biomarkers do not appear to be a suitable objective indicator of mental fatigue in the applied sporting environment. Practitioners should work to identify and manage mental fatigue with the same level of importance given to the periodisation of physical fatigue.

Fatigue in Aviation: Safety Risks, Preventive Strategies and Pharmacological Interventions

Fatigue poses an important safety risk to civil and military aviation. In addition to decreasing performance in-flight (chronic) fatigue has negative long-term health effects. Possible causes of fatigue include sleep loss, extended time awake, circadian phase irregularities and work load. Despite regulations limiting flight time and enabling optimal rostering, fatigue cannot be prevented completely. Especially in military operations, where limits may be extended due to operational necessities, it is impossible to rely solely on regulations to prevent fatigue. Fatigue management, consisting of preventive strategies and operational countermeasures, such as pre-flight naps and pharmaceuticals that either promote adequate sleep (hypnotics or chronobiotics) or enhance performance (stimulants), may be required to mitigate fatigue in challenging (military) aviation operations. This review describes the pathophysiology, epidemiology and effects of fatigue and its impact on aviation, as well as several aspects of fatigue management and recommendations for future research in this field.