MENTAL WORKLOAD AND COGNITIVE TASK AUTOMATICITY - AN EVALUATION OF SUBJECTIVE AND TIME-ESTIMATION METRICS

The evaluation of mental workload is becoming increasingly important i n system design and analysis. The present study examined the structure and assessment of mental workload in performing decision and monitori ng tasks by focusing on two mental workload measurements: subjective a ssessment and time estimation. The task required the assignment of a s eries of incoming customers to the shortest of three parallel service lines displayed on a computer monitor. The subject was either in charg e of the customer assignment (manual mode) or was monitoring an automa ted system performing the same task (automatic mode). In both cases, t he subjects were required to detect the non-optimal assignments that t hey or the computer had made. Time pressure was manipulated by the exp erimenter to create fast and slow conditions. The results revealed a m ulti-dimensional structure of mental workload and a multi-step process of subjective workload assessment. The results also indicated that su bjective workload was more influenced by the subject's participatory m ode than by the factor of task speed. The time estimation intervals pr oduced while performing the decision and monitoring tasks had signific antly greater length and larger variability than those produced while either performing no other tasks or performing a well practised custom er assignment task. This result seemed to indicate that time estimatio n was sensitive to the presence of perceptual/cognitive demands, but n ot to response related activities to which behavioural automaticity ha s developed.