Time perception as a workload measure in simulated car driving

In experimental studies using flight simulations subjects’ duration estimates have shown to be an effective indicator of cognitive task demands. In this study we wanted to find out whether subjective time perception could serve as a measure of cognitive workload during simulated car driving. Participants drove on a round course of a driving simulator consisting of three different environments with different levels of task demands. Drivers were required to perform a time-production task while driving the vehicle. Electrodermal activity and subjective ratings of mental workload (SWAT) were recorded simultaneously. The length of produced intervals increased significantly in more complex driving situations, as did electrodermal activity and subjective ratings of mental workload. Thus, time production is a valid indicator of cognitive involvement in simulated driving and could become a valid method to measure the current mental workload of car drivers in various traffic situations.     

Effects of different physical workload parameters on mental workload and performance

The design and evaluation of an occupational task should include an assessment of mental workload, since excessive levels of mental workload can cause errors or delayed information processing. Physically demanding work that is performed concurrently with a cognitive task may impact mental workload by impairing mental processing or decreasing performance. The primary objective of this study was to determine whether there is a differential effect of various types of physical activity on both mental workload and cognitive performance. Objective and subjective assessment tools (heart rate variability and visual analog scale) were used as indicators of mental workload, while correct responses during an arithmetic task reflected levels of performance. Thirty participants (ages 18-24 years) performed a combination of tasks inducing both physical and mental workload. Type of physical effort, frequency of movement, and force exertion level were manipulated to alter the workload associated with the physical activity. Changes in subjective ratings generally corresponded to changes in both performance on the arithmetic task and objective mental workload assessment. Some discrepancies occurred at the highest physical force exertion level as participants perceived an increase in effort to maintain the same level of performance. Further research is needed to determine the force exertion threshold, beyond which the physical effort required interferes with mental workload and/or cognitive performance.

Relevance to industry

Technological advancements have increased the requirement for many workers to execute cognitive tasks concurrently with physical activity. When designing and evaluating such situations it is important to determine the interactive effects of these activities. A simple, uni-dimensional tool is suggested as a screening tool to identify situations requiring excessive or increased mental workload that many degrade performance or place additional stress on the individual.     

Assessment and monitoring of mental workload in subway train operations using physiological,subjective, and performance measures

Subway train operation is a complex, sociotechnical system that involves a variety of cognitively demanding tasks. The train operators are responsible for continuously monitoring the surrounding environment, maintaining awareness, processing information, and making decisions under risk. The resulting mental strain on operators can negatively affect their performance and the interaction of the human–machine system. The objective of this study was to evaluate if physiological, subjective, and performance measures could identify the level of mental workloads arising from routine and nonroutine operations in the subway system. A total of 11 subway train operators underwent different driving scenarios in a high‐fidelity simulator. The simulated tasks were divided into two categories: routine operations (preparing to drive and driving between stations without interruptions or emergencies) and nonroutine operation (responding to a tunnel fire, dealing with a high density of passengers, encountering a passenger/technician on the track, and responding to train failure). The mental workload was monitored and evaluated in these tasks using an electrocardiogram, subjective self‐rating scales, and driving performance. Both heart rate variability and performance measures (including reaction time and error rate) detected mental workload variations in the different operations. On the other hand, the subjective ratings (including NASA‐TLX) assessed the overall mental workload associated with a task, without explaining the mental demand variations within the task over time. Subway train drivers experienced different levels of mental workload during routine and nonroutine driving conditions. The findings of this study can be used to extract mental workload limits to optimize workload levels during train operations.     

An experimental evaluation of instantaneous self-assessment as a measure of workload

Instantaneous self-assessment (ISA) is a technique that has been developed as a measure of workload to provide immediate subjective ratings of work demands during the performance of primary work tasks such as air traffic control. This paper reports a study that compared the results of ISA with those gathered from other established workload evaluation techniques; subjective ratings collected at the end of the task, mean heart rate and heart rate variability, and error in the primary task of tracking. ISA ratings were found to be correlated significantly with the post-task ratings of workload, heart rate variability, and task performance. Generally each of the techniques was sensitive to variations in task difficulty. However, performance on the primary tracking task was found to be poorer during periods when ISA responses were required, regardless of whether they were spoken or manual responses. This finding suggests that the usefulness of the technique is limited in comparison to less intrusive measures of workload.     

Measuring Mental Workload Using ERPs Based on FIR,ICA, and MARA

Mental workload is considered to be strongly linked to human performance, and the ability to measure it accurately is key for balancing human health and work. In this study, brain signals were elicited by mental arithmetic tasks of varying difficulty to stimulate different levels of mental workload. In addition, a finite impulse response (FIR) filter, independent component analysis (ICA), and multiple artifact rejection algorithms (MARAs) were used to filter event-related potentials (ERPs). Then, the data consisting of ERPs, subjective ratings of mental workload, and task performance, were analyzed through the use of variance and Spearman’s correlation during a simulated computer task. We found that participants responded faster and performed better in the easy task condition, followed by the medium and high-difficulty conditions, which verifies the validity of the ERP filtering. Moreover, larger P2 and P3 waveforms were evoked as the task difficulty increased, and a higher task difficulty elicited a more enhanced N300. Correlation analysis revealed a negative relationship between the amplitude of P3 and the subjective ratings, and a positive relationship between the P3 amplitude and accuracy. The results presented in this paper demonstrate that a combination of FIR, ICA, and MARA methods can filter ERPs in the non-invasive real-time measurement of workload. Additionally, frontocentral P2, N3, and parietal P3 components showed differences between genders. The proposed measurement of mental workload can be useful for real-time identification of mental states and can be applied to human–computer interaction in the future.     

Mental workload and cognitive task automaticity: an evaluation of subjective and time estimation metrics

Abstract

The evaluation of mental workload is becoming increasingly important in system design and analysis. The present study examined the structure and assessment of mental workload in performing decision and monitoring tasks by focusing on two mental workload measurements: subjective assessment and time estimation. The task required the assignment of a series of incoming customers to the shortest of three parallel service lines displayed on a computer monitor. The subject was either in charge of the customer assignment (manual mode) or was monitoring an automated system performing the same task (automatic mode). In both cases, the subjects were required to detect the non-optimal assignments that they or the computer had made. Time pressure was manipulated by the experimenter to create fast and slow conditions. The results revealed a multi-dimensional structure of mental workload and a multi-step process of subjective workload assessment. The results also indicated that subjective workload was more influenced by the subject's participatory mode than by the factor of task speed. The time estimation intervals produced while performing the decision and monitoring tasks had significantly greater length and larger variability than those produced while either performing no other tasks or performing a well practised customer assignment task. This result seemed to indicate that time estimation was sensitive to the presence of perceptual/cognitive demands, but not to response related activities to which behavioural automaticity has developed.     

Cultural influences on the measurement of subjective mental workload

Cognitive ergonomics is well entrenched in North American and most European work environments, where systems and products are designed with the capabilities and limitations of the user in mind. A prominent technique for analysing task demands is subjective mental workload measurement. Subjective ratings of mental workload have been shown—in North American and European populations—to be reliable and sensitive to changes in mental workload. However, there is reason to think that cultural differences may affect subjective ratings. This study compared the performance and subjective mental workload ratings of Indonesian (n = 87) and Dutch (n = 88) students in the context of a hybrid memory/visual search task. Performance was comparable for the two groups, but the sensitivity of the subjective workload measures was better in the Dutch than in the Indonesian group. The results are interpreted in light of social axioms and cultural values.

Statement of Relevance: Now more than ever ergonomists must think beyond national borders in improving work processes. Globalisation requires that cultural differences be taken into account in developing and applying ergonomic techniques. This paper presents empirical work showing that cultural differences seriously impact the sensitivity of mental workload measures.     

Vigilance requires hard mental work and is stressful

OBJECTIVE: We describe major discoveries and developments in vigilance research. BACKGROUND: Vigilance tasks have typically been viewed as undemanding assignments requiring little mental effort. The vigilance decrement function has also been considered to result from a decline in arousal brought about by understimulation. METHODS: Recent research in vigilance is reviewed in four areas: studies of task type, perceived mental workload during vigilance, neural measures of resource demand in vigilance, and studies of task-induced stress. RESULTS: Experiments comparing successive and simultaneous vigilance tasks support an attentional resource theory of vigilance. Subjective reports also show that the workload of vigilance is high and sensitive to factors that increase processing demands. Neuroimaging studies using transcranial Doppler sonography provide strong, independent evidence for resource changes linked to performance decrement in vigilance tasks. Finally, physiological and subjective reports confirm that vigilance tasks reduce task engagement and increase distress and that these changes rise with increased task difficulty. CONCLUSIONS: Converging evidence using behavioral, neural, and subjective measures shows that vigilance requires hard mental work and is stressful. APPLICATION: This research applies to most human-machine systems that require human monitoring, particularly those involving automated subsystems.     

Evaluating the effect of perceived mental workload on work body postures

Mental workload is a multidimensional construct that involves the characteristics of the task, individual factors, and the environment where the task is performed. Responses to tasks that are perceived as mentally demanding can exacerbate ergonomics risk factors affecting employee behavior and attitude, leading to risky actions such as awkward body postures, and consequently increasing physiological susceptibility to work-related musculoskeletal disorders. The present study looked to establish if the perception of mental workload can be affected by psychosocial work factors that generate changes in the environment in which humans must perform the tasks. The study also looked to determine if changes in perceived mental workload generated changes in the body postures undertaken to perform an activity to lay the foundation for future exploration into the influence of perceived mental workload over physical demands. The results of this study indicate, that an increase in the perception of mental workload is associated with worse body postures. This study is novel and contributes to overcoming an important shortcoming in the field of mental workload by considering the influence of psychosocial factors, keeping the physical load constant, on the perception of mental workload and its influence on body postures. This interaction between perceived mental workload and its effects on physical risk should be considered in occupational settings since often, employees are exposed to concurrent physical and mental demands that increase the likelihood of developing WMSDs.     

Measuring pilot workload in a motion base trainer. A comparison of four techniques

Various techniques have been developed to predict and measure pilot workload. This simulation was conducted in order to compare four widely used methods: a visual two-and four-choice reaction time task, time production, retrospective multi-dimensional subjective ratings and in-flight verbal workload estimates. Two scenarios with different levels of difficulty determined by preliminary research were designed to test these techniques. The insertion of the secondary tasks did not significantly affect flight performance. All four techniques were able to distinguish between the overall levels of scenario complexity. In addition, the three secondary tasks and workload ratings obtained in-flight were generally able to distinguish among levels of difficulty for different segments within the scenarios.     

Assessing mental workload in virtual reality based EOT crane operations: A multi-measure approach

BackgroundEye-movement metrics and subjective workload measures are extensively used to determine mental workload of participants. The aim of this study was to assess Electric overhead travelling (EOT) crane operators’ mental workload variability based on eye movement metrics such as fixation frequency, fixation duration, saccade duration, saccade amplitude, and fixation/saccade ratio during EOT crane operations in virtual reality (VR) based EOT crane simulator.MethodsA 2^k (k = 3) factorial experiment with factors namely, hazardous scenario, activity level, and trial was designed and conducted to demonstrate the proposed assessment approach. Throughout the experiment, we recorded the eye movements of 12 EOT crane operators of a steel industry of authors’ country. Post experiment, the National Aeronautics and Space Administration task load index (NASA-TLX) was adopted as a subjective workload measure and run time of task completion was recorded. Eye-movement metrics, subjective workload measure, run time were tested with multivariate analysis of variance (MANOVA), and three way repeated measure analysis of variance (ANOVA).ResultsAt the level of α = 0.05, the experimental factors significantly influence the means of eye movement metrics, subjective ratings and run time. There was also significant influence among their interactions. A positive correlation was also found for eye movements metrics with NASA-TLX and run time.ConclusionsEye movement metrics help in understanding the mental workload of participants unobtrusively and continuously. Analysis of subjective workload measure and run time along with eye-gaze analysis provide a deeper understanding on the pattern of mental workload.     

An analysis of relational complexity in an air traffic control conflict detection task

Theoretical analyses of air traffic complexity were carried out using the Method for the Analysis of Relational Complexity. Twenty-two air traffic controllers examined static air traffic displays and were required to detect and resolve conflicts. Objective measures of performance included conflict detection time and accuracy. Subjective perceptions of mental workload were assessed by a complexity-sorting task and subjective ratings of the difficulty of different aspects of the task. A metric quantifying the complexity of pair-wise relations among aircraft was able to account for a substantial portion of the variance in the perceived complexity and difficulty of conflict detection problems, as well as reaction time. Other variables that influenced performance included the mean minimum separation between aircraft pairs and the amount of time that aircraft spent in conflict.     

An analysis of relational complexity in an air traffic control conflict detection task

Theoretical analyses of air traffic complexity were carried out using the Method for the Analysis of Relational Complexity. Twenty-two air traffic controllers examined static air traffic displays and were required to detect and resolve conflicts. Objective measures of performance included conflict detection time and accuracy. Subjective perceptions of mental workload were assessed by a complexity-sorting task and subjective ratings of the difficulty of different aspects of the task. A metric quantifying the complexity of pair-wise relations among aircraft was able to account for a substantial portion of the variance in the perceived complexity and difficulty of conflict detection problems, as well as reaction time. Other variables that influenced performance included the mean minimum separation between aircraft pairs and the amount of time that aircraft spent in conflict.     

Perceived fatigue after mental work: an experimental evaluation of a fatigue inventory

The aim of this study was to investigate the perceived fatigue after mental work and to test the Swedish Occupational Fatigue Inventory (SOFI). Twenty male and 20 female participants worked with proof reading (2 x 90 min) and a vigilance task (2 x 60 min). After each task session, perceived fatigue was rated with the SOFI and Borg's CR10O-scale. In addition, physiological reactions were registered; blood pressure, heart rate, heart rate variability and muscle activity in corrugator supercilii, as well as measures of performance: reaction time, number of pages read and number of proof errors found, number of detected signals. As expected, the highest ratings were obtained on Lack of energy, Lack of motivation and Sleepiness, particularly after the vigilance task. High ratings after both work tasks were also found on the CR10-scale. Men and women did not differ significantly with respect to their ratings. No clear-cut physiological reactions were found to correlate with ratings of fatigue. The results indicate the validity of the mental dimension of the SOFI.     

Monitoring of mental workload levels during an everyday life office-work scenario

Personal and ubiquitous healthcare applications offer new opportunities to prevent long-term health damage due to increased mental workload by continuously monitoring physiological signs related to prolonged high workload and providing just-in-time feedback. In order to achieve a quantification of mental load, different load levels that occur during a workday have to be discriminated. In this work, we present how mental workload levels in everyday life scenarios can be discriminated with data from a mobile ECG logger by incorporating individual calibration measures. We present an experiment design to induce three different levels of mental workload in calibration sessions and to monitor mental workload levels in everyday life scenarios of seven healthy male subjects. Besides the recording of ECG data, we collect subjective ratings of the perceived workload with the NASA Task Load Index (TLX), whereas objective measures are assessed by collecting salivary cortisol. According to the subjective ratings, we show that all participants perceived the induced load levels as intended from the experiment design. The heart rate variability (HRV) features under investigation can be classified into two distinct groups. Features in the first group, representing markers associated with parasympathetic nervous system activity, show a decrease in their values with increased workload. Features in the second group, representing markers associated with sympathetic nervous system activity or predominance, show an increase in their values with increased workload. We employ multiple regression analysis to model the relationship between relevant HRV features and the subjective ratings of NASA-TLX in order to predict the mental workload levels during office-work. The resulting predictions were correct for six out of the seven subjects. In addition, we compare the performance of three classification methods to identify the mental workload level during office-work. The best results were obtained with linear discriminant analysis (LDA) that yielded a correct classification for six out of the seven subjects. The k-nearest neighbor algorithm (k-NN) and the support vector machine (SVM) resulted in a correct classification of the mental workload level during office-work for five out of the seven subjects.     

Effects of control order,augmented feedback,input device and practice on tracking performance and perceived workload

Virtual interfaces to advanced human-machine systems will present operators with a variety of perceptual-motor challenges. To inform the virtual interface design processes, the present experiments examined the effects of track order, level of knowledge of performance, type of control device, and the extent of practice on tracking performance and associated mental workload. Tracking was assessed by root mean square error. Subjective workload was measured using both the NASA Task Load Index (TLX) and the Subjective Workload Assessment Technique (SWAT). Results indicated non-linear effects, where tracking error and subjective workload both increased non-proportionally with track order. Trackball use resulted in more accurate performance and was judged to be of lower subjective workload than input using a mouse. Augmented knowledge of performance had little effect on either performance or workload. There were a number of interactions affecting performance that were replicated in perceived workload. Over acquisition trials, second-order tracking exhibited continuous improvement. This capability was retained even after a 30-day rest interval. Decrease in workload followed performance improvement in both initial acquisition and subsequent retention phases. The two subjective workload scales were essentially equivalent in terms of their sensitivity to task manipulations. These results support the direct association between workload and performance and confirms the use of workload in helping to evaluate the influence of diverse task-related demands. The implications for the design of virtual interfaces to real-world systems are examined in the light of these findings.     

Perceived fatigue after mental work: an experimental evaluation of a fatigue inventory

The aim of this study was to investigate the perceived fatigue after mental work and to test the Swedish Occupational Fatigue Inventory (SOFI). Twenty male and 20 female participants worked with proof reading (2x90 min) and a vigilance task (2x60 min). After each task session, perceived fatigue was rated with the SOFI and Borg's CR10-scale. In addition, physiological reactions were registered; blood pressure, heart rate, heart rate variability and muscle activity in corrugator supercilii, as well as measures of performance: reaction time, number of pages read and number of proof errors found, number of detected signals. As expected, the highest ratings were obtained on Lack of energy, Lack of motivation and Sleepiness, particularly after the vigilance task. High ratings after both work tasks were also found on the CR10-scale. Men and women did not differ significantly with respect to their ratings. No clear-cut physiological reactions were found to correlate with ratings of fatigue. The results indicate the validity of the mental dimension of the SOFI.     

Human information processing during physical exercise.

This study was designed to investigate how conditions of physical exercise affect human information processing. Sixteen subjects performed two information processing tasks (perception and decision) during two exercise conditions (endurance vs interval protocols) and during two control conditions (rest vs minimal load protocols). The control conditions required subjects either to perform the information processing tasks under resting conditions or while pedalling a bicycle ergometer at a minimal workload. Workload during the exercise protocols consisted of a fixed percentage of the subject's maximal workload. Each 40 min protocol consisted of five consecutive stages: practice, baseline, warming-up, exercise, and cooling-down, during which heart rate and ratings of perceived exertion were determined. In the perception task subjects had to identify a briefly presented row of three letters. In the decision task subjects had to indicate which of the outer numbers in a row of three digits was the larger. Results indicated that the two control protocols did not influence cognitive task performance; however, in the exercise protocols, increments in physical workload improved performance on the decision task and reduced performance on the perception task, while decrements in physical workload reduced performance on the decision task and improved performance on the perception task. Changes in mental task performance were not evident within protocol stages; only after stage transitions did changes in mental performance occur. We discussed possible theoretical approaches to explain these results and concluded that models advanced in the context of dual-task methodology seem most promising.     

Effect of varying levels of mental workload on startle eyeblink modulation

Previous research using punctuate reaction time and counting tasks has found that the startle eyeblink reflex is sensitive to attentional demands. The present experiment explored whether startle eyeblink is also modulated during a complex continuous task and is sensitive to different levels of mental workload. Participants (N = 14) performed a visual horizontal tracking task either alone (single-task condition) or in combination with a visual gauge monitoring task (multiple-task condition) for three minutes. On some task trials, the startle eyeblink reflex was elicited by a noise burst. Results showed that startle eyeblink was attenuated during both tasks and that the attenuation was greater during the multiple-task condition than during the single-task condition. Subjective ratings, endogenous eyeblink rate, heart period, and heart period variability provided convergent validity of the workload manipulations. The findings suggest that the startle eyeblink is sensitive to the workload demands associated with a continuous visual task. The application of startle eyeblink modulation as a workload metric and the possibility that it may be diagnostic of workload demands in different stimulus modalities is discussed.     

Selected graph design variables in four interpretation tasks: a microcomputer-based pilot study

A pilot study was undertaken to assess the efficacy of selected graph types and information coding schemes in producing quick and accurate graph interpretation. Point-plots, line graphs, bar graphs, and three-dimensional bar graphs were constructed and displayed using an IBM-PC microcomputer with colour monitor. The effectiveness of each of these graph types, as well as the coding scheme used within each (colour versus monochrome), was investigated using 32 subjects in four separate experiments involving either point-reading, point-comparison, trend-reading, or trend-comparison tasks. Dependent measures including task completion time, graph interpretation error, subjective mental workload rating, and graph preference rating were obtained. In three of the tasks, colour-coded graphs were associated with lower task completion time, lower rated mental workload, and higher rated preference than monochrome graphs. However, there were no differences in subjects' error scores between colour and monochrome coding for any of the tasks. For the point-reading task, the three-dimensional bar graphs were less effective than the other graph types, though there were no differences among graph types for the other three tasks. Implications for graph design given specific data interpretation tasks are discussed, based on the results of the four experiments and related literature.