Clark A. Shingledecker

Application of conjoint measurement to workload scale development

Practical considerations make subjective opinion one of the most widely used methods to assess mental workload. However, the value of the data obtained by subjective methods is often limited because scales are not standardized and are not based on modern psychometric principles. This paper describes the development and validation of a Subjective Workload Assessment Technique (SWAT) which uses conjoint measurement to construct interval level workload scales from ordinal rankings of combinations of levels on three contributory dimensions. An experiment was conducted to investigate the construct validity and concurrent validity of the SWAT-1 scale. Recommendations for further development are discussed.

Subjective Workload Assessment in a Memory Update Task

Twelve subjects performed a short-term memory task under several difficulty levels and rated the workload associated with each condition using the Subjective Workload Assessment Technique (SWAT). SWAT ratings proved more sensitive than memory error to task difficulty variations in all but one of the most difficult memory conditions. Most importantly, SWAT ratings demonstrated their greatest relative sensitivity at the lowest levels of workload. The results are interpreted as supporting the applicability of SWAT as a sensitive workload index.

Workload Measurement in System Design and Evaluation

Because of its central role in system development, workload measurement has been extensively researched. These efforts have produced a variety of workload assessment techniques, many of which can be classified as either subjective, physiological, or behavioral measures. These categories of measures can vary along several dimensions that can be used as criteria in selection of a technique for a particular application. The proposed selection criteria include the sensitivity, diagnosticity, and intrusiveness associated with a technique. Different stages of system design can require techniques that differ on the noted dimensions. Since no technique is capable of meeting all of the applicable criteria, a comprehensive approach to workload assessment will require a battery of subjective, physiological, and behavioral measures. Future research dealing with comparative evaluation of the various assessment techniques along the noted dimensions will be required in order to refine workload metric selection criteria.

Standardized Tests for the Evaluation and Classification of Workload Metrics

Although a variety of metrics are available for workload assessment, little research has been conducted to construct guidelines for optimally matching them to individual workload questions or test environments. In an effort to remedy this problem, AFAMRL is currently developing a standardized methodology which will be used to evaluate candidate workload measures on several theoretical and pragmatic criteria. The central feature of this methodology is a set of representative loading tasks. This paper outlines the analyses that were conducted to screen potential components of the Criterion Task Set (CTS) and describes the tasks which were selected to produce demands on a number of functional dimensions of information processing.

Effect of workload on the auditory evoked brainstem response

The purpose of this study was to explore the effect of workload level of a grammatical reasoning task on the auditory brainstem evoked response. Ten male subjects were administered three difficulty levels of a grammatical reasoning task. Brainstem evoked responses were recorded before and after the randomly presented workload conditions, as well as during each workload condition. The results revealed a consistent increase in Wave VI latency during all workload conditions, but no apparent differentiation between workload conditions. Post-test brainstem measures revealed that latency of Wave VI did not recover to pre-test baseline levels.

Methods and Systems for Measuring Human Performance Capabilities

Human factors specialists require practical efficient data collection technologies which can be used to answer questions about the performance capabilities of the human operator. This paper considers several factors which contribute to the interpretability, sensitivity, and practical utility of standardized task batteries designed to assess the effects on human performance of work environments, stressors, biochemically active agents and performance enhancement interventions. The procedures employed in the development of a task battery by the U.S. Air Force Aerospace Medical Research Laboratory are used to illustrate both the theoretical and pragmatic issues which are discussed.

Combined stress and human performance: a weighted digraph model

Abstract Weighted directed graphs are described and offered as possible aids to the analysis of the interactive effects of multiple independent variables on human behavior. Examples in which weighted digraphs represent the interactions among multiple stressors and performance indices are presented, and pulse process analysis is used to derive empirical predictions from the models.