Index Pupil Activity Echoing with Task Difficulty in Fitts' Law Setting

Research has found that changes in mental workload during both cognitive and motor tasks can be indicated by pupil dilation. To measure cognitive workload, researchers have developed tools such as the wavelet analysis-based index of cognitive activity (ICA) and index of pupil activity (IPA). However, it is still unclear whether these tools can accurately measure workload during motor tasks. This study aims to investigate whether the IPA can differentiate task workload during a motor task involving aiming in a tele-operation setting, where the task requirements were quantified using Fitts' index of difficulty(ID) based on target size and distance. The study found that the IPA can differentiate between different levels of motor task workload, provided the proper window is used, namely the period before the tool touches the targets. This finding is significant as it can aid in developing objective methods to evaluate task workload using pupil parameters during goal-directed movements.