Exploring Normative Eye Movement Patterns in Functional Tasks

Abstract

When interacting with an object, humans are quite effective at navigating their hand to an object, grasping it, and acting on it. The level of ease with which we do this masks the complex interplay of sensory modalities that is occurring. This study utilizes a head-mounted eye-tracker and upper-limb motion capture markers to reveal how one of these sensory modalities, vision, enables efficient object interaction. Participants completed several trials of two tasks mimicking real-world demands. The first task involved turning and grasping a pasta box from an original position outside the participant’s field of view and placing it onto two shelves before returning it to its starting location. The second task had participants move cups filled with beads four times over a partition. Both tasks show participants spend nearly the full duration of the trial fixating on objects relevant to the task, well in advance of their hand arriving at an object. As well, participants spend little time fixating on their own hand when reaching towards an object, and slightly more time, although still very little, fixating on the object in their hand when transporting it. Instead, during a grasp, participants make a saccade from the object to its drop-off location, and hold this fixation until the object is being released by the hand. Other sensory systems, likely proprioception and haptic feedback, allow participants to behave this way. When interacting with an object outside the field of view, slight changes in this behavior occur. Specifically, participants are unable to fixate on the object as far in advance of their hand, move slightly slower, and increase their maximum grip aperture. A possible explanation for these behaviours is a predictable interaction between covert and overt attention, Dorsal and Ventral Streams of visual processing, and proprioceptive and haptic feedback that allow individuals to carry out object interactions in a smooth, cyclical manner with the eyes leading the hand.