State of science: mental workload in ergonomics

Young, Mark S.; Brookhuis, Karel; Wickens, Christopher D.; Hancock, Peter A. · 2014 · Ergonomics

DOI: 10.1080/00140139.2014.956151

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Summary

This paper reviews the state of science regarding mental workload (MWL) in ergonomics, addressing its definition, measurement, and application over the last three decades. The authors highlight that MWL is a critical yet nebulous concept, particularly as modern technology shifts workplace demands from physical to cognitive. The review aims to synthesize contemporary knowledge to clarify how MWL impinges on performance and to identify current challenges, such as quantifying workload "redlines" and understanding the interaction between mental and physical loads. The authors analyze the evolution of MWL research through a bibliometric review of the Ergo-Abs database, noting a threefold increase in references since the 1980s. Conceptually, MWL is defined as the balance between task demands (stress) and available operator resources (strain), mediated by factors like skill, automation, and experience. The paper distinguishes between overload, which causes distraction and insufficient processing time, and underload, which leads to reduced alertness and attentional lapses. Both extremes degrade performance, suggesting an optimal range of workload for best outcomes. Measurement approaches are categorized into three types: primary and secondary task performance (e.g., peripheral detection tasks), subjective self-reports (e.g., NASA-TLX), and physiological metrics (e.g., heart rate variability, EEG, and eye movements). The authors note that these measures often dissociate, meaning they do not always correlate, which provides valuable insights into the discrepancy between perceived and objective workload. Findings from the bibliometric analysis reveal a shift in research focus from measurement techniques in the 1980s to theoretical modeling in the 1990s, and finally to real-world applications in the 2000s. Transport-related applications, particularly driving, aviation, and rail, dominate recent literature. Driving research has expanded to include studies on vehicle automation, mobile phone use, and age differences, while rail and air traffic control research focuses on automation and traffic volume impacts. The authors emphasize that MWL assessment has become influential in regulatory contexts, such as bans on handheld mobile phone use while driving. The significance of this review lies in its identification of emerging challenges for the field. The authors argue that future research must address the integration of mental and physical workload metrics and the development of neuroergonomic techniques, such as brain-computer interfaces and near-infrared spectroscopy, to monitor operators in real-time. A primary goal is to define precise performance thresholds or "redlines" that indicate when operators are approaching overload or underload. By clarifying the multidimensional nature of MWL and advancing measurement technologies, the field can better design complex, safety-critical systems that maintain operator performance within optimal limits.

Key finding

Mental workload research has shifted from theoretical and measurement-focused studies in the 1980s and 1990s to applied research in the 2000s, with transport applications, especially driving, becoming the dominant area of study.

Methodology

review

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Topics

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• mental demand
• capacity resource theory
• workload measurement

Information type

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• Methodological Resource: metric or index
• Theoretical Contribution: theory or model