A tool for measuring mental workload during prosthesis use: The Prosthesis Task Load Index (PROS-TLX)

When using a prosthesis, a high level of mental, emotional, and physical effort is experienced. These have been linked to high rates of device dissatisfaction and rejection. Therefore, understanding and quantifying the complex nature of mental workload experienced when using, or learning to use, a prosthesis has practical and clinical importance for researchers and applied professionals. The aim of this paper was to design and validate a self-report measure of mental workload specific to prosthesis use (The Prosthesis Task Load Index; PROS-TLX) that encapsulates the array of mental, physical and emotional demands often experienced by users of these devices. We first surveyed prosthetic limb users who confirmed the importance of eight workload constructs taken from published literature and previous workload measures. These constructs were mental demands, physical demands, visual demands, conscious processing, frustration, situational stress, time pressure and device uncertainty. Able-bodied participants wearing eye tracking equipment completed a task requiring them to pick up coins and place them into a jar first using their anatomical hand and then using a myoelectric prosthetic hand simulator with and without time pressure. Performance times were slower, more coins were dropped and there were more hand-focused fixations when using the prosthesis with and without added time pressure, compared to when participants used their anatomical hand. These changes in performance were reflected in significant increases in PROS-TLX workload subscales as predicted. The scale was also found to have good convergent and divergent validity. Overall, the PROS-TLX captures the multidimensional nature of the cognitive, physical and emotional workload experienced by prosthesis users and provides a practical tool for use in both future research and clinical practice.