Psychophysiological Metrics for Workload are Demand-Sensitive but Multifactorial

Various psychophysiological indices of mental workload exhibit sensitivity to task demand factors, but the psychometrics of indices has been neglected. In particular, the extent to which different metrics converge on a common latent factor is unclear. In the present study, 150 participants performed in four task scenarios based on a simulation of unmanned vehicle operation. Scenarios required threat detection and/or change detection. Both single- and dual-task scenarios were used. Workload metrics were derived from the electroencephalogram (EEG), electrocardiogram (ECG), transcranial Doppler sonography (TCD), functional Near Infra-Red (fNIR) and eyetracking. Subjective workload was also assessed. Several metrics were appropriately sensitive to the differing levels of task load presented by the four scenarios. However, factor analysis identified multiple factors, each of which was associated with a single response system only, with no general factor. Caution should be used in assessing workload in the individual operator

Perceived Time as a Measure of Mental Workload:Effects of Time Constraints and Task Success

The mental workload imposed by systems is important to their operation and usability. Consequently, researchers and practitioners need reliable, valid, and easy-to-administer methods for measuring mental workload. The ratio of perceived time to clock time appears to be such a method, yet mental workload has multiple dimensions of which the perceived time ratio has mainly been linked to the task-related dimension. This study investigates how the perceived time ratio is affected by time constraints, which make time an explicit concern in the execution of tasks, and task success, which is a performance-related rather than task-related dimension of mental workload. A higher perceived time ratio is found for timed than untimed tasks. According to subjective workload ratings and pupil-diameter measurements, the timed tasks impose higher mental workload. This finding contradicts the prospective paradigm, which asserts that perceived time decreases with increasing mental workload. A higher perceived time ratio was also found for solved than unsolved tasks, whereas subjective workload ratings indicate lower mental workload for the solved tasks. This finding shows that the relationship between the perceived time ratio and mental workload is reversed for task success compared to time constraints. Implications for the use of perceived time as a measure of mental workload are discussed. 1

Weighing the importance of drivers’ workload measurement standardization

Workload is an inescapable topic within the context of Human-Machine Interaction (HMI). Evolution dictates that HMI systems will be all the more attractive to users the more intuitive they are. While attempting to create an optimized workload management system, the authors have encountered a difficulty in gathering a homogeneous definition of workload and a standardized manner of measuring it. In fact, some researchers even call into question the fact that maybe different things are being discussed. Could it be the underlying cause of many of the HMI failures so far recorded? Either way, the weight this concept carries is too heavy to be dealt lightly. It is very important that standardized strategies for measurement of workload are developed so that, for one, different results can be compared and contribute to a more robust understanding of the concept and that, for two, the measurement of workload is globalized and able to be adapted to all users.This work has been supported by European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project nº 039334; Funding Reference: POCI-01-0247- FEDER-039334]