Pupil responses to continuous aiming movements

Pupillary response is associated with perceptual and cognitive loads in visual and cognitive tasks, but no quantitative link between pupil response and the task workload in visual-motor tasks has been confirmed. The objective of this study is to investigate how the changes of task requirement of a visual-motor task are reflected by the changes of pupil size. In the present study, a simple continuous aiming task is performed and the task requirement is manipulated and measured by Fitts' Index of Difficulty (ID), calculated for different combinations of the target size and movement distance. Pupil response is recorded using a remote eye-tracker. The results show that event-triggered pupil dilations in continuous aiming movements respect Fitts' Law, such that higher task difficulty evokes higher peak pupil dilation and longer peak duration. These findings suggest that pupil diameter can be employed as a physiological indicator to task workload evoked by the task requirement in visual-motor tasks. Pupil responses correlate to task difficulty in continuous aiming movements.Pupil size changes can indicate the mental workload evoked by physical tasks.Movement-related pupil response was detected from self-paced visual-motor tasks.The task difficulty of the motor task was quantitatively defined using Fitts' law.The pupillary measure was expanded from cognitive workload to physical workload.