The objective of this study is to develop a quantified method for determining the mental workload imposed on train control officers (TCOs) and to express this mental workload by means of an index that is objective and can stand up to the tests of validity and reliability. The method addresses an existing operational shortcoming in Spoornet train control operations and could be used as a tool for predicting the mental workload imposed on operators at particular train control centres. The method could be applied to manage and improve operational safety in the rail transport environment. A participative systems approach was followed in the development of the measuring methodology. A work group comprising expert users of the specific train control system was involved in identifying task factors and assigning weights for task and moderating factors. The newly developed Mental Workload Index (MWLI) consists of three task factors and eleven moderating factors, each with a different weight in terms of its contribution to overall mental workload. The work group performed several iterations to reach final consensus on the following task factors and their respective contributions to the MWLI: the number of data transactions, the number of authorisations, and the number of communications via telephone and radio. The systems approach used in the development process is discussed, and the final index with the task and moderating factors is presented. In conclusion, the value and possible application of the MWLI are discussed. The MWLI is shown to provide an objective method for the assessment and prediction of mental workload in the train control environment. / Thesis (PhD)--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / unrestricted

Multiple devices such as desktops, laptops, and cell phones are often used to manage users' personal information, such as files, calendars, contacts, emails, and bookmarks. This dissertation presents the results of two studies that examined users' mental workload in this context, especially when transitioning tasks from one device to another. In a survey of 220 knowledge workers, users reported high frustration with current devices' support for task migration, e.g. making files available on multiple machines. To investigate further, I conducted a controlled experiment with 18 participants. While they performed PIM tasks, I measured their mental workload using subjective measures and physiological measures. Some systems provide support for transitioning users' work between devices, or for using multiple devices together; I explored the impact of such support on mental workload and task performance. Participants performed three tasks (Files, Calendar, Contacts) with two treatment conditions each (lower and higher support for migrating tasks between devices.) This dissertation discusses my findings: workload measures obtained using the subjective NASA TLX scale were able to discriminate between tasks, but not between the two conditions in each task. Task-Evoked Pupillary Response, a continuous measure, was sensitive to changes within each task. For the Files task, a significant increase in workload was noted in the steps before and after task migration. Participants entered events faster into paper calendars than into an electronic calendar, though there was no observable difference in workload. For the Contacts task, task performance was equal, but mental workload was higher when no synchronization support was available between their cell phone and their laptop. Little to no correlation was observed between task performance and both workload measures, except in isolated instances. This suggests that neither task performance metrics nor workload assessments alone offer a complete picture of device usability in multi-device personal information ecosystems. Traditional usability metrics that focus on efficiency and effectiveness are necessary, but not sufficient, to evaluate such designs. Given participants' varying subjective perceptions of these systems and differences in task-evoked pupillary response, aspects of hot cognition such as emotion, pleasure, and likability show promise as important parameters in system evaluation. / Ph. D.

Workers experience combined physical and mental demands in their daily jobs, yet the contribution of these concurrent demands in the development of work-related musculoskeletal disorders (WMSDs) is not clearly understood. There is a need to understand how concurrent demands interact with different work parameters, such as force levels, muscles employed, and types of exertion, to influence physiological responses. Furthermore, whether muscle capacity is altered with these concurrent demands remains unclear. The current research was conducted to address these needs through three experimental studies that evaluated changes in physiological, performance, and subjective measures. The first study investigated muscle-specific responses to concurrent physical and mental demands during intermittent static work. Mental demands adversely affected physiological responses with increasing physical demand. Furthermore, greater motor and mental performance impairment was observed at either end of the physical demand spectrum. Finally, these interactions were muscle-dependent, with postural (shoulder and torso) muscles indicating a greater propensity to interference due to concurrent demands than executive (wrist) muscles. The aim of the second study was to evaluate differential effects of exertion type (static and dynamic) during concurrent physical and mental work. Concurrent physical and mental demands adversely affected physiological responses during static exertions compared to dynamic exertions. Furthermore, static exertions were more susceptible to decrements in muscle output and mental task performance than dynamic exertions, specifically at higher force levels. The last study quantified the effects of concurrent physical and mental demands on muscle capacity (endurance, fatigue, and recovery) during intermittent static work. Additional mental processing was associated with shorter endurance times, greater strength decline, increased fatigability, and slower cardiovascular recovery. Concurrent demand conditions were also associated with higher levels of perceived fatigue, and rapid increases in rates of perceived exertion, time pressure, mental load, and stress. Overall, the current research provides a comprehensive understanding of the interactive effects of physical and mental demands on physiological responses and task performance. These findings may facilitate the development of task design strategies to help reduce the risk of workplace injuries and to increase worker performance. Finally, outcomes from this research can contribute towards the revision of current ergonomic guidelines to incorporate concurrent assessment of physical and mental demands. / Ph. D.

New sensor and display technologies are expected to enhance the performance of soldiers by providing them more information about the battlefield. However, there is concern that greater quantities of information and increases in mental workload might cause distraction, reduce attention to dangers in the immediate environment, and threaten soldier survival. The purpose of this laboratory investigation was to quantify the effects of increases in mental workload on one of the soldier's most basic tasks --- avoiding ground hazards while walking. The participants were 12 U.S. Army infantry soldiers. The study was conducted on a treadmill that was modified to provide the participants a view of impending ground hazards up to 5 meters forward of their walking position. The study was a 2X3 fixed factor design with two levels of terrain difficulty (No Hazards and Hazards) and three levels of mental workload (No Load, Moderate load, and High load), all as within-subject effects. Mental workload was increased from the "No Load" to a "Moderate" level by requiring the participants to perform a mental arithmetic task while walking. Mental workload was increased from the "Moderate" to the "High" level of load by increasing the difficulty of arithmetic problems. The dependent variables included time and error in the performance of the mental arithmetic task, the mean and standard deviation in step length and step rate, the number of ground hazards contacted, and subjective ratings of workload. The participants" scores on the Armed Forces Qualification Test (AFQT) and subtests of the Armed Services Vocational Aptitude Battery (ASVAB) related to arithmetic skills were also obtained. The results of the investigation indicated that when the participants were required to avoid hazards, step length decreased and step rate increased, as was expected. Both measures of gait increased in variability. Subjective ratings of physical demand and effort obtained across the three levels of mental workload increased significantly, along with perceptions of workload associated with a perceived decline in performance. Subjective ratings obtained across the two levels of terrain difficulty indicated that ratings of mental demand and effort increased with each increase in level of mental workload. When the participants were confronted with the more difficult arithmetic problems at the "High" level of mental workload, time and error in performing the mental arithmetic task increased as did ratings of temporal demand, frustration, and workload attributable to a perceived decline in performance; however, subjective ratings of physical demand decreased. Interactions found between terrain difficulty and mental workload indicated that differences in ratings of performance and overall workload scores between the two levels of terrain difficulty decreased significantly between the "No Load" and the "Moderate" level of mental workload, and converged at the "High" level of mental load. Although relationships were found between perceived workload, gait, and performance of the mental arithmetic and hazard avoidance tasks, the analysis did not reveal a significant effect of mental workload on the number of hazards contacted. Some participants tended to contact more hazards at the "High" level of mental workload than at the "No Load" or the "Moderate" levels, as expected. However, other participants tended to contact more hazards at the "Moderate" level of mental load than at either of the two extremes. Still other participants tended to contact more hazards at the "No Load" level of mental workload than at the "Moderate" or the "High" levels. Correlations were found between subjective ratings of workload, mental arithmetic performance, and scores on the AFQT and subtests of the ASVAB related to arithmetic skills, but no relationships were found between test scores and performance of the hazard avoidance task. However, when test scores were used as covariates in the analysis of mental arithmetic performance, the findings revealed that the number of correct responses to the arithmetic problems decreased when the participants were required to avoid hazards. The results of the study may support the belief that the allocation of limited resources will vary based on past experience and other individual differences, and that the amount of resources allocated to a task may be influenced by the difficulty of the task, criteria for performance, and the motivation of the individual. / Master of Science

This research evaluated mental schema accuracy, user experience, and training methods of computer based tasks using educational software. Aims were to investigate the impact of mental schemas on individuals’ usability of technology and analyze the impact of training and user experience in terms of mental schemas and performance. Study one investigated schema accuracy as a predictor of perceived usability and mental workload; by analyzing the accuracy of users’ mental schema through task correctness. Task was found to be a significant predictor of the measures of usability, along with various demographic variables. When considering the effect of tasks, schema accuracy was a significant predictor of perceived usability and mental workload for task two (online quiz). Perceived usability showed lower values indicating higher perceptions of usability for task two and mental workload had lower values indicating reduced mental workload for task two. Significant, positive correlations were found between perceived usability and mental workload. Findings show schema accuracy as a preliminary measure of users’ subjective usability of non-problem solving tasks, based on the type of task tested and demographic data of students. Study two examined experience level (experienced and un-experienced) effects mental schema accuracy, robustness, completion time, and errors using three computer-based tasks. Experienced participants showed lower values for number of errors and robustness than un-experienced users. Significant, positive correlations were found between schema accuracy and completion time, and errors and completion time. The findings support the use of experience to analyze the impact of mental schemas and performance measures. Study three explored the change in training methods (no-training, paper, or video) on user changes in mental schema accuracy, robustness, completion times and errors. Training improved robustness, specifically paper-based training. Performance results showed that students who spent small periods of time using the software more times a week had made fewer errors and had more robust schemas. Demographic experience categories found that participants who spent more time using the software had fewer errors. Significant, positive correlations were found between schema accuracy and robustness. These results show that training improves mental schema robustness and reduces the number of errors while completing computer based tasks.

<p>  </p> <p>Some of the variability found in measures of mental workload (see e.g. Singleton et al. 1973; Wierwille and Connor 1983; Steelman-Allen et al. 2011; Casner and Gore 2010) may be due to the effort applied to the task by participants, rather than by the independent variable of interest. If true, capturing and removing the variation due to ‘applied effort’ could improve the ability of studies to detect effects of interest. </p> <p>While introducing participants to two sub-tasks derived from Multi-Attribute Task Battery II (Santiago-Espada et al. 2011), the study investigated the influence of applied effort on MATB-II performance measures of mental workload while holding other effects constant. Two groups of participants each completed easy and hard trials of MATB-II-derived sub-tasks. Treatment group of participants was offered an additional reward if they achieved a sufficiently high performance.</p> <p>The treatment group performed better by just under 4% in both easy and hard trials which provides a suggestion about the size of the effect of applied effort in this study. </p> <p>Additionally pilot error analysis was performed using Tracking task results. Error probability distributions did not fit known distributions and did not show consistent difference between treatment and control groups. Novel method of distribution “tails” comparison showed significant difference in extreme error durations, extents and delays between treatment and control groups.</p> <p>Measuring or controlling for applied effort can improve the ability of researchers to determine the effects of interventions on workload measures by reducing the amount of variability that is captured as error. Also, “tails” method seems to be a viable tool in comparing probability  </p>

The aim of the research was to develop the non-intrusive physiological measure of using human facial skin temperature change as an indicator of mental workload. The forehead and nose temperature were obtained via thermography from the participants who drove in a simulator driving environment and/or in instrumented car experiments. The NASA TLX and the Modified Cooper-Harper metrics were adopted to assess the subjective workload for the validation of the physiological measure. Three driving experiments were conducted in order to acquire the physiological response and the workload score for the performed tasks. Forehead temperature was very stable throughout the experiments. Nose temperature dropped significantly after the experimental drive for all conditions in simulator test. Experiment 1 (NASA TLX Group: N=10; MCH Group: N=14) used simulator driving with different terrains as loading tasks. Neither the significant difference of the subjective workload nor the temperature drop was detected between different terrain conditions. In experiment 2 (N=33), mental workload was increased in a controlled manner by the introduction of mental arithmetic tests to the primary simulated drive. The mental arithmetic test conditions provoked a significantly greater nose temperature drop and also a higher perceived workload than the conditions without the arithmetic test. A weak correlation between the nose temperature drop and the subjective workload metric was yielded from the experiments. In Experiment 3 (N=13), facial temperature response and subjective workload score were compared between the simulator test and on-road driving. Driving in the simulator resulted in higher subjective workload and greater nose temperature drop than in real-car driving. When participants perceived a higher workload for a task, their nose temperature exhibited a greater drop. A significant correlation between the nose temperature change and the subjective workload score was found. Actual or potential applications of this research include real-time and unobtrusive mental workload assessment for human-system interaction development.

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The complexity and broadening of competencies have led to a number of assessment frameworks that advocate for the use of rater judgment in direct observation of clinical performance. The degree to which these assessment processes produce scores that are valid, are therefore vitally dependent on a rater’s cognitive ability. A number of theories suggest that many of the cognitive structures needed to complete rating tasks are capacity limited and may therefore become a source of difficulty when rating demands exceed resources. This thesis explores the role of rating demands on the performance and behaviour of raters in the assessment of clinical competence and asks: in what way do rating demands associated with rating clinical performance affect rater performance and behaviour? I hypothesized that as rating demands increase, rating performance declines and raters engage in cognitive avoidance strategies in order to complete the task. I tested this hypothesis by manipulating intrinsic and extraneous sources of load for raters in the assessment of clinical performance. Results consistently demonstrated that intrinsic load, specifically broadening raters’ focus by increasing the number of dimensions to be considered simultaneously, negatively affected indicators of rating quality. However, extraneous demands failed to result in the same effect in 2 of 3 experiments. When we explored the cognitive strategies raters engage under high load conditions we learned of a number of strategies to reduce cognitive work, including idiosyncratically minimizing intrinsic demands (leading to poor inter-rater reliability) and active elimination of sources of extraneous load, explaining both findings. When we induced extraneous load in manner that could not be easily minimized by raters, we also found impairments in rater performance, specifically the provision of feedback. I conclude that rating demands, whether induced intrinsically or by extraneous sources, impair rater performance affecting both the utility of scores and the opportunity for learner development. Implications for health professions education and future directions are discussed. / Dissertation / Doctor of Philosophy (PhD)

Workload is defined as the cost incurred by an individual, given their capacities, while achieving a particular level of performance on a task with specific demands. Demands of a task or combination of tasks may include maintaining postural stability, executing physical actions, and/or performing cognitive tasks. While there have been attempts to establish a physiological measure of concurrent physical and mental workload, as yet there has been no work towards developing a single subjective method of evaluation. Select subjective assessment methodologies were evaluated quantitatively during laboratory-based experiments. Concurrent execution of mental and physical activity was required at various levels, since it was desired to be able to measure mental workload, physical workload, and also evaluate their interaction. Measurements of task performance were investigated to evaluate the effects of combined mental and physical demands and establish which subjective assessments were accurate and sensitive to changes in workload. The utility of existing subjective assessment tools created for one domain appeared to be limited when evaluating multi-task situations requiring substantial mental and physical activity. Further clarification of the impact of different types of physical demand on cognitive processing, performance and subjective workload assessment of a constant mental task was addressed in the second experiment. This experiment investigated the effect of several activity types, specifically global versus localized effort, changes in load, and different task frequencies. The results provided support that the type of activity, load and frequency of task influence subjective mental workload assessment scores and performance. Not all existing assessment tools accurately represented an individual's ability to perform a task when there was a combination of physical and mental demands. A unidimensional tool is suggested as a screening tool to identify situations requiring excessive or increased mental workload. Alternative methods, possibly a new multidimensional tool, should be developed to obtain more detailed information so ratings of workload for different tasks may be compared. Effectiveness of a subjective stability assessment tool was evaluated in situations demanding mental activity while maintaining an upright posture. Tests were performed over a wide range of conditions, including various mental loads, sensory conditions, and postural stances. The purpose was to determine the effects of each task variation on the perception of postural stability. Postural sway increased with task difficulty, regardless of the source (i.e. postural stance, visual condition, mental workload). The addition of mental workload did not alter the non-linear relationship between objective measures of postural sway and perceptions of postural stability. Since decrements in balance are well perceived, subjective assessment tools may be incorporated in control strategies to minimize falls. / Ph. D.