: This report reviews research on physiological metrics of mental workload performed in the last decade. The focus of the review is on measurement techniques that have potential for fundamental explanation of mental workload and for use in operational environments. The techniques are examined within a framework of measurement criteria. These criteria include: sensitivity, diagnosticity, intrusiveness, reliability, and generality of application. Over 200 articles are covered by the review. Measures reviewed include: electroencephalograms, event-related potentials, magnetoencephalograms, positron emission tomography, electro-oculograms, cardiovascular measures, pupillometry, respiratory measures, and electrodetmal measures. Keywords: Mental workload, Physiological metrics, Electroencephalogram, Magnetoencephalogram, Cardiovascular function, Pupillometry, Respiration, Electrodermal responses.

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Physiological metrics of mental workload: A review of recent progress

A theory is presented to identify sources that produce dissociations between performance and subjective measures of workload. The theory states that performance is determined by (1) amount of resources invested, (2) resource efficiency, and (3) degree of competition for common resources in a multidimensional space described in the multiple-resources model. Subjective perception of workload, multidimensional in nature, increases with greater amounts of resource investment and with greater demands on working memory. Performance and subjective workload measures dissociate when greater resources are invested to improve performance of a resource-limited task; when demands on working memory are increased by time-sharing between concurrent tasks or between display elements; and when performance is sensitive to resource competition and subjective measures are more sensitive to total investment. These dissociation findings and their implications are discussed and directions for future research are suggested.

Dissociation of performance and subjective measures of workload

Previous studies of dual-task coordination in working memory have shown a lack of dual-task interference when a verbal memory task is combined with concurrent perceptuomotor tracking. Two experiments are reported in which participants were required to perform pairwise combinations of (1) a verbal memory task, a visual memory task, and perceptuomotor tracking (Experiment 1), and (2) pairwise combinations of the two memory tasks and articulatory suppression (Experiment 2). Tracking resulted in no disruption of the verbal memory preload over and above the impact of a delay in recall and showed only minimal disruption of the retention of the visual memory load. Performing an ongoing verbal memory task had virtually no impact on retention of a visual memory preload or vice versa, indicating that performing two demanding memory tasks results in little mutual interference. Experiment 2 also showed minimal disruption when the two memory tasks were combined, although verbal memory (but not visual memory) was clearly disrupted by articulatory suppression interpolated between presentation and recall. These data suggest that a multiple-component working memory model provides a better account for performance in concurrent immediate memory tasks than do theories that assume a single processing and storage system or a limited-capacity attentional system coupled with activated memory traces.

/pdf/concurrent-performance-of-two-memory-tasks-evidence-for-511hai8tfq.pdf

Concurrent performance of two memory tasks: evidence for domain-specific working memory systems.

The concept of mental workload has long been recognized as an important factor in individual performance within complex systems. It is documented that either overload or underload may degrade performance, and further affect the efficiency of the whole system. Therefore, systems designers need some explicit models to predict the mental workload imposed on individuals by the system at an early design phase so that alternative system designs can be evaluated. In examining mental-workload literature, it is found that few predictive mental-workload models have considered factors specific to individuals. This research aims to develop a practical framework for predicting mental workload in both single- and multi-task environments considering such individual factors. In order to describe mental workload more precisely and more completely, a framework for mentalworkload definitions, which contains instantaneous workload, average workload, accumulated workload, peak workload and overall workload, is proposed. In or...

Review and reappraisal of modelling and predicting mental workload in single- and multi-task environments

The purpose of the present study was to analyse the effects of information complexity on Pilot Mental WorkLoad (PMWL) and Pilot Performance (PP), and to analyse the structure of PMWL. Eighteen pilots performed 72 simulated low level-high speed emissions. The complexity of the Head Down Display (HDD) information varied as a function of the tactical situation. Flight data were recorded continuously. The pilots' eye movements were video taped and psychophysiological activation data, Heart Rate (HR), were obtained. The pilots rated PMWL according to the psychological content of three scales (Bedford Rating Scale, Subjective Workload Assessment Technique, NASA-Task Load indeX) and answered a questionnaire tapping aspects of performance, information load, motivation and mood. It was found that even a moderate complexity of information interfered with the flight task. Altitude and variation in altitude were increased and corrections of altitude errors were delayed, when complexity increased. Changes in informati...

Information complexity--mental workload and performance in combat aircraft.

A theory of the dissociation between subjective measures of mental workload and performance is described. The theory proposes that subjective measures are heavily driven by the number of tasks or task elements that a subject must perform concurrently. However they are relatively less sensitive to whether these tasks compete for common or separate resources, and to the difficulty of a single task, particularly if this difficulty is related to response factors. Performance, on the other hand, is particularly influenced by single task difficulty of both a perceptual and response nature and by resource competition between tasks. A set of three experiments are described to examine the dissociation between subjective difficulty measures and performance. These experiments employ different combinations of three tasks: tracking, memory search, and a simulated air traffic control problem. The results supported all forms of dissociation predicted by the theory and the implications of results to workload measurement are discussed.

The dissociation between subjective workload and performance: a multiple resource approach

This paper responds to some of the criticisms presented by Kantowitz and Weldon (1985) that have been directed toward the methodology used in a 1981 article by Wickens, Mount-ford, and Schreiner. We state here that some of their criticisms are valid: A performance operating characteristic (POC) cannot be derived from a single point in a POC space, and therefore resource competition cannot be separated from concurrence cost as a source of task interference. However, we also note that the primary issue of importance to system designers---how to compare interference between different tasks---is not answered by Kantowitz and Weldon's critique. That issue requires that some technique for standardizing performance decrements across tasks be assumed. Two alternate techniques for standardizing are described in the present paper.

POCs and performance decrements - A reply to Kantowitz and Weldon

A set of three experiments are described that examine the sources of information processing that produce a dissociation between subjective workload measures and performance. The results support a theory of the dissociation. Subjective measures are driven more by the number of tasks currently performed. Subjective measures are also less sensitive to resource competition than performance measures are. Factors that demand more resource investment improve performance, but these factors also increase subjective ratings of workload.

Why do performance and subjective workload measures dissociate

The study of operator performance in manual and automated versions of dynamic decision tasks is proposed. The two microcomputer paradigms of simple and complex, dynamic scheduling tasks are described. Error detection accuracy and latency of assignment, and fault detection and correction for the two tasks are to be analyzed.

Yei-Yu Yeh

Papers

The dissociation between subjective workload and performance: a multiple resource approach

POCs and performance decrements - A reply to Kantowitz and Weldon

Why do performance and subjective workload measures dissociate

A comparison of operator performance in manual and automated versions of a dynamic decision-making task