Mental Workload

The level of mental workload experienced by operators is a key element in the safety, reliability, and efficiency of complex sociotechnical systems (Gregoriades and Sutcliffe, 2007). Mental workload is a contentious area, and there has been great debate over how to define the concept. It is generally agreed that human operators possess a finite attentional capacity and that during task performance these atten-tional resources are allocated to component tasks. Workload is thus a function of the human operator s attentional capacity and the demand for resources imposed by the task. The level of mental workload represents the proportion of resources that are required to meet the task demands (Welford, 1978). Young and Stanton (2001) formally defined mental workload as follows The mental workload of a task represents the level of attentional resources required to meet both objective and subjective performance criteria, which may be mediated by task demands, external support, and past experience. Mental workload is therefore a multidimensional construct that is characterized by the task (e.g., complexity, demands) and the individual involved (e.g., skill, experience, training). 

When operators are faced with excessive task demands and their attentional resources are exceeded, they become overloaded. Mental overload therefore occurs when the demands of the task are so great that they are beyond the limited attentional capacity of the operator. Conversely, when operators experience excessively low task demands, they may experience a state of mental underload. Both conditions can be detrimental to task performance (Wilson and Rajan, 1995) because operators become less likely to attend to potentially important sources of information (Lehto and Buck, 2008). 

Various consequences associated with inappropriate levels of workload can potentially lead to performance decrements. These include inattention, complacency, fatigue, monotony, mental saturation, mental satiation, reduced vigilance, and stress. The Health and Safety Executive stated that for mental workload, conditions of over and under-arousal should be avoided. The duration of tasks that have an associated low or high level of mental workload should be limited. Both these extremes will increase the likelihood of human error affecting the system (HSE, 2008). 

Ostensibly, then, there is an optimal level of workload for optimal task performance, and system and procedural designers should aim to optimize operator workload to ensure efficient task performance. Many human factors practitioners have cited workload optimization as being critical to maintaining effective task performance in complex systems (e.g.. Young and Stanton, 2002 Sebok, 2000). Workload optimization involves achieving a balance between task demands and operator resources. 

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From the 1960s onward, there was a greater interest in psychological issues, dominated by the concept of the human as a single-channel processor of information. This stimulated research into a number of areas. Studies of mental workload were concerned with the ability of humans to cope with extremely high levels of information in situations such as air traffic control. Vigilance studies, which focused on the human s role in situations with very low levels of stimulation such as radar monitoring, represented the other extreme of human performance that was considered. 

Decision making may involve calculations, reference to procedures and past experience, and other demands on long-term memory. This contributes further to the overall mental workload. From the HF/E perspective, many errors are likely to arise from information processing overload, essentially from the mismatch between demands and capabilities. Information-processing demands can be reduced by the provision of information in the form of job aids such as flow charts or decision trees. 

Signal-flow graphs are particularly useful in two respects. First, they make the process designer examine in considerable detail the dynamic structure and fimctioning of the process. Second, the nature of the interface between person and machine can be seen more clearly. The variables that are displayed in a system are, of course, available for study, but workers frequently respond to derivative functions of variables or "hidden" variables that must be deduced. Given that the process variables to be displayed will influence the worker s control strategy and that the number of deductions to be made will affect the mental workload involved, a process designer can select the type and amoimt of process information which will enhance performance of the task. 

Moray, N. (Ed.) (1979). Mental Workload, Its Theory and Measurement. New York Plenum Press. 

Wierwille, W. W., Eggemeier (1993). Recommendations for Mental Workload Measurement in a Test and Evaluation Environment. Human Factors 35(2), 263-281. 

Could we provide supports that would decrease mental workload and mitigate degraded performance, and how ... 

Cook, J., and Salvendy, G. (1999), Job Enrichment and Mental Workload in Computer-Based Work Imphcation for Adaptive Job Design, International Journal of Industrial Ergonomics, Vol. 24, pp. 13-23. 

Extensions of This Approach to Simulating Crew Mental Workload... 

P3 latency Mental workload imposed by additional tasks in simulated flight Fowler (1994) S... 

HR Mental workload in real flight in command, with practice Kakimoto et al. (1988) F... 

Mental workload in pilots during abnormal situations Large changes in mental workload during simulated flight... 

Salivary cortisol Mental workload in real flight Kakimoto et al. 

Backs, R. W., Walrath, L. C. (1992). Eye movement and pupillary response indices of mental workload during visual search of symbolic displays. Applied Ergonomics, 23, 243-254. 

Boucsein, W. (1993). Psychophysiology in the computer workplace—goals and methods. In P Ullsperger (Ed.), Psychophysiology of mental workload (pp. 35-42). Berlin Schriftenreihe der Bundesanstalt fiir Arbeitsmedizin, Sonderschrifl2. 

Hankins, T C., Wilson, G. E. (1998). A comparison of heart rate, eye activity, EEG and sul ective measures ofpilot mental workload during flight vlviartow, Space, and Environmental Medicine, 69, 360-367. 

Hohnsbein, J., Falkenstein, M., Hoormann, J. (1995). Effects of attention and time-pressure on P300 subcomponents and implications for mental workload leseatch. Biological Psychology, 40, 73-81. 

Itoh, Y., (feHayashi, Y. (1990). The ergonomic evaluation ofeye movement and mental workload in aircraft pilots. 719-733. 

Kramer, A. F., Trejo, L. J., Humphrey, D. (1995). Assessment of mental workload with task-irrelevant auditory probes. Bto/ogica/Piyc/to/ogy, 40, 83-100. 

Svensson, E., Angelborg-Thanderz, M., Sjoberg, L., Olsson, S. (1997). Information complexity—mental workload and performance in combat aircraft. 

Veltman, J. A., Gaillard, A. W K. (1993). Indices of mental workload in a complex task environment. Neuropsychobiology, 28, 72-75. 

Wierwille, W. W., Rahimi, M., Casali, J. G. (1985). Evaluation of 16 measures of mental workload using a simulated flight task emphasizing mediational activity. Human Factors, 27, 489-502. 

The two research lines described here constitute the baseline for the most important approaches in engineering psychophysiology the investigation of mental workload with psychophysiological indices and the investigation of the work-health relationship in stress research. An outline of these two approaches is given in the next two sections. 

As discussed in the previous section, mental workload has been defined in terms of an interaction between the demands of the task and the ability of an individual to fulfill these demands in a accurate and timely fashion (Gopher ... 

Wilson, Swain, 1996 Stern Dunham, 1990) ate sensitive to variations in mental workload, but not diagnostic with regard to specific varieties of workload that may be involved in the person-task interaction. 

One important topic for future research is the interaction or interplay between energetical mechanisms and psychological resources that comprise the construct of mental workload. Given that psychophysiological measures appear to reflect both general and specific aspects of workload, they provide a potentially ideal methodology with which to examine the control and deployment of... 

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