Theo F. Meijman

Mental fatigue, motivation and action monitoring

In this study we examined whether the effects of mental fatigue on behaviour are due to reduced action monitoring as indexed by the error related negativity (Ne/ERN), N2 and contingent negative variation (CNV) event-related potential (ERP) components. Therefore, we had subjects perform a task, which required a high degree of action monitoring, continuously for 2h. In addition we tried to relate the observed behavioural and electrophysiological changes to motivational processes and individual differences. Changes in task performance due to fatigue were accompanied by a decrease in Ne/ERN and N2 amplitude, reflecting impaired action monitoring, as well as a decrease in CNV amplitude which reflects reduced response preparation with increasing fatigue. Increasing the motivational level of our subjects resulted in changes in behaviour and brain activity that were different for individual subjects. Subjects that increased their performance accuracy displayed an increase in Ne/ERN amplitude, while subjects that increased their response speed displayed an increase in CNV amplitude. We will discuss the effects prolonged task performance on the behavioural and physiological indices of action monitoring, as well as the relationship between fatigue, motivation and individual differences.

Error-related ERP components and individual differences in punishment and reward sensitivity

Although the focus of the discussion regarding the significance of the error related negatively (ERN/Ne) has been on the cognitive factors reflected in this component, there is now a growing body of research that describes influences of motivation, affective style and other factors of personality on ERN/Ne amplitude. The present study was conducted to further evaluate the relationship between affective style, error related ERP components and their neural basis. Therefore, we had our subjects fill out the Behavioral Activation System/Behavioral Inhibition System (BIS/BAS) scales, which are based on Grays (1987, 1989) biopsychological theory of personality. We found that subjects scoring high on the BIS scale displayed larger ERN/Ne amplitudes, while subjects scoring high on the BAS scale displayed larger error positivity (Pe) amplitudes. No correlations were found between BIS and Pe amplitude or between BAS and ERN/Ne amplitude. Results are discussed in terms of individual differences in reward and punishment sensitivity that are reflected in error related ERP components.

The relation between work-induced neuroendocrine reactivity and recovery, subjective need for recovery, and health status

OBJECTIVES The purpose of this cross-sectional study with repeated measurements was to find out to what extent neuroendocrine reactivity during work and neuroendocrine recovery from work, and work characteristics, are related to subjective need for recovery and perceived health status. METHODS Neuroendocrine reactivity and recovery were studied in 59 subjects by measuring urinary adrenaline and cortisol repeatedly during five consecutive days. Measures of work characteristics, subjective need for recovery, and health status were obtained by self-reports. Two hierarchical multiple linear regression analyses were performed. RESULTS The work characteristics alone explained 39% and 28% of the variation in subjective need for recovery and health status, respectively, while these figures rose to 49% and 53% in the full models. Significant neuroendocrine contributors were found for cortisol in reactivity during work and recovery immediately after work and recovery during the day off-work, and for adrenaline in baseline level and recovery during the day off-work. Job characteristics contributed significantly as well. CONCLUSION Both neuroendocrine measures and work characteristics were predictors for the amount of perceived need for recovery after work as well as for health status. The results are consistent with the cognitive activation theory of stress.

Motor fatigue and cognitive task performance in humans

During fatiguing submaximal contractions a constant force production can be obtained at the cost of an increasing central command intensity. Little is known about the interaction between the underlying central mechanisms driving motor behaviour and cognitive functions. To address this issue, subjects performed four tasks: an auditory choice reaction task (CRT), a CRT simultaneously with a fatiguing or a non‐fatiguing submaximal muscle contraction task, and a fatiguing submaximal contraction task alone. Results showed that performance in the single‐CRT condition was relatively stable. However, in the fatiguing dual‐task condition, performance levels in the cognitive CRT deteriorated drastically with time‐on‐task. Moreover, in the fatiguing dual‐task condition the rise in force variability was significantly larger than during the fatiguing submaximal contraction alone. Thus, our results indicate a mutual interaction between cognitive functions and the central mechanisms driving motor behaviour during fatigue. The precise nature of this interference, and at what level this interaction takes place is still unknown.

Cortisol secretion throughout the day, perceptions of the work environment, and negative affect

The effects of explanatory variables derived from a work stress model (the effort-reward imbalance model) on salivary cortisol were assessed. A multilevel analysis was used to distinguish the effects of single occasion and multiple occasion measurements of work stress and effect on cortisol. The single (or cross-sectional) factors include Effort-Reward Imbalance (ERI), need for control, negative affect, and other enduring factors (type of occupation, gender, and smoking). The multiple occasion measurements include momentary negative mood, Momentary Demand-Satisfaction Ratio (MD-SR), sleep quality, work load (workday versus day off), at work (versus not being at the workplace), and lunch. The effect of time of day on cortisol was controlled for before the effects of these variables were determined.Momentary negative mood but not trait negative affect was positively associated with ambulatory measured cortisol. The variables from the work stress model—effort, reward, need for control, and the multiple occasion measurements of demand and satisfaction—did not affect cortisol. As could be expected, time of day had an effect on cortisol, but a hypothesised interaction with momentary negative mood was not found. Additionally, the results show that the time course of cortisol differs between individuals and that the effect of sleep quality on cortisol can vary from person to person. This points to the necessity of continued efforts to single out sources of individual variability.The finding that variables derived from the effort-reward imbalance model are not related with cortisol does not support the hypothesis that ERI leads to short-term changes in cortisol, indicating no relation with hypothalamic-pituitary-adrenal (HPA) axis activity. On the other hand, the present results invite further qualification of negative affect as a potential determinant of HPA activity, at least, as far as can be deduced from cortisol measurements.

Task engagement and the relationships between the error-related negativity, agreeableness, behavioral shame proneness and cortisol

Previous results suggest that both cortisol mobilization and the error-related negativity (ERN/Ne) reflect goal engagement, i.e. the mobilization and allocation of attentional and physiological resources. Personality measures of negative affectivity have been associated both to high cortisol levels and large ERN/Ne amplitudes. However, measures of positive social adaptation and agreeableness have also been related to high cortisol levels and large ERN/Ne amplitudes. We hypothesized that, as long as they relate to concerns over social evaluation and mistakes, both personality measures reflecting positive affectivity (e.g. agreeableness) and those reflecting negative affectivity (e.g. behavioral shame proneness) would be associated with an increased likelihood of high task engagement, and hence to increased cortisol mobilization and ERN/Ne amplitudes. We had female subjects perform a flanker task while EEG was recorded. Additionally, the subjects filled out questionnaires measuring mood and personality, and salivary cortisol immediately before and after task performance was measured. The overall pattern of relationships between our measures supports the hypothesis that cortisol mobilization and ERN/Ne amplitude reflect task engagement, and both relate positively to each other and to the personality traits agreeableness and behavioral shame proneness. We discuss the potential importance of engagement-disengagement and of concerns over social evaluation for research on psychopathology, stress and the ERN/Ne.

Vagal cardiac control throughout the day: the relative importance of effort-reward imbalance and within-day measurements of mood, demand and satisfaction

The effects of variables derived from a work stress theory (the effort-reward imbalance theory) on the power in the high frequency (HF_HRV) band of heart rate (0.14-0.40 Hz) throughout a work day, were determined using multilevel analysis. Explanatory variables were analysed at two levels: at the lowest level (within-day level), the effects of positive mood, negative mood, demand, satisfaction, demand-satisfaction ratio, and time of day were assessed. At the highest level (the subject level), the effects of sleep quality, effort, reward, effort-reward imbalance, need for control, type of work (profession), negative affectivity, gender and smoking on HF_HRV were assessed. Need for control has a negative effect on HF_HRV after controlling for time of day effects, i.e. subjects with a high need for control have a lower vagal control of the heart. In the long run, these subjects may be considered to be at increased health risk, because they have less of the health protective effects of vagal tone. The interaction between effort-reward imbalance and time of day has a positive effect on HF_HRV, i.e. the cardiac vagal control of subjects with a high effort-reward imbalance increases as the day progresses. It is discussed that this probably reflects reduced effort allocation, ensuing from disengagement from the work demands.

Mental fatigue and the efficiency of information processing in relation to work times

Abstract Mental fatigue was studied by analysing performance and mental effort in a memory search task in relation to the temporal structuring of preceding work periods. Performance was measured by reaction time and error rate. Mental effort was measured via spectral analysis of the 0.10 Hz component in the heart rhythm signal. It was shown that subjects protected their performance by spending more effort in the unfavorable conditions: after several hours of work and after continuous work without short rest breaks. In the most unfavorable condition, after 8 h of work combined with sleep loss, the efficiency of information processing broke down. Performance could no longer be protected by invested effort. This breakdown phenomenon is interpreted as a serious sign of mental fatigue. Relevance to industry The present study describes a method of analysing mental fatigue, based on the analysis of the performance related to the mental effort invested in a standard memory-search task. This method could be applied in the practical evaluations of work systems.

Adaptive strategy changes as a function of task demands: a study of car drivers

When drivers perform additional tasks while driving, research shows conflicting results: primary driving performance may deteriorate but adaptive changes such as reducing driving speed have also been noted. We hypothesized that the nature of the secondary task may be important: drivers may give more priority to tasks that serve goals of the driving task itself, for example route finding, than tasks not directly relevant for driving, for example tuning the radio. The main objective of the present driving simulator study was to test this hypothesis. Twenty subjects performed two different subsidiary tasks while driving through two levels of traffic density: a working memory (WM) task and a map reading (MAP) task. It was hypothesized that in high task demand situations, the WM task, irrelevant for the driving task, would be neglected more than the MAP task. The results confirmed the hypothesis: in MAP conditions, the WM task was indeed neglected, but map reading resulted in more swerving, indicating that the subjects looked at the map despite the high task demands. It is concluded that drivers will be highly motivated to get route information, and RG systems should therefore present their information in a readily understandable format.

Maintaining task set under fatigue: a study of time-on-task effects in simulated driving

An experiment was carried out in a driving simulator in order to study time-on-task effects in driving with special attention to distance keeping and hazard avoidance performance. As expected, increases of fatigue in the course of sustained performance were associated with a deterioration of perceptual-motor performance and an increase of safety margins. In general, the results indicate that performance in less central task components such as steering deteriorates in the course of time, whereas performance in high-priority sub-tasks such as hazard avoidance remains intact. Time-schedule instructions disrupted the adaptation of safety margins in prolonged driving. This study has practical implications for the design of driver impairment monitoring systems.