Effects of control order, augmented feedback, input device and practice on tracking performance and perceived workload

Virtual interfaces to advanced human-machine systems will present operators with a variety of perceptual-motor challenges. To inform the virtual interface design processes, the present experiments examined the effects of track order, level of knowledge of performance, type of control device, and the extent of practice on tracking performance and associated mental workload. Tracking was assessed by root mean square error. Subjective workload was measured using both the NASA Task Load Index (TLX) and the Subjective Workload Assessment Technique (SWAT), Results indicated non-linear effects, where tracking error and subjective workload both increased non-proportionally with track order. Trackball use resulted in more accurate performance and was judged to be of lower subjective workload than input using a mouse. Augmented knowledge of performance had little effect on either performance or workload. There were a number of interactions affecting performance that were replicated in perceived workload. Over acquisition trials, second-order tracking exhibited continuous improvement. This capability was retained even after a 30-day rest interval. Decrease in workload followed performance improvement in both initial acquisition and subsequent retention phases. The two subjective workload scales were essentially equivalent in terms of their sensitivity to task manipulations. These results support the direct association between workload and performance and confirms the use of workload in helping to evaluate the influence of diverse task-related demands. The implications for the design of virtual interfaces to real-world systems are examined in the light of these findings.