Human Eyes Move to the Target Earlier When Performing an Aiming Task with Increasing Difficulties

Abstract

We examined whether human operators move their eyes earlier to a target before hands when the level of task difficulty increases. We hypothesized that participants would perform less proactive eye movements in the difficult task than in the easy one, as they would need to focus more on their current hand movements. Sixteen university students were recruited to perform the aiming and touching task reciprocally on three paired targets (circles) differing in sizes and distances, while had their eye movements tracked. The movement time, the early eye engagement time (EEET), and the number of eye adjustments were recorded. The EEET was defined as the time that a subject’s eyes fix on a target to the moment that the tool reaches out for it. The movement time increased as the index of difficulty (ID) value increased, echoing with the Fitts’ Law prediction. When aiming to a target with a higher ID, participants’ EEET was longer comparing to when reaching for a target with a lower ID. Participants reduced the movement speed to give themselves a longer time in searching visually for the target information before moving their hands. In contrast to our hypothesis, results suggested a proportional relationship between the task difficulty and the early eye engagement time. Participants also performed an increasing number of eye adjustments over the course of moving from the easy to the hard target. Future research is needed to examine eye hand coordination under the regulation of Fitts’ Law.