Abstract
Most object manipulation tasks involve a series of actions demarcated by mechanical contact events, and gaze is usually directed to the locations of these events as the task unfolds. Typically, gaze foveates the target 200 ms in advance of the contact. This strategy improves manual accuracy through visual feedback and the use of gaze-related signals to guide the hand/object. Many studies have investigated eye-hand coordination in experimental and natural tasks; most of them highlighted a strong link between eye movements and hand or object kinematics. In this experiment, we analyzed gaze strategies in a collision task but in a very challenging dynamical context. Participants performed collisions while they were exposed to alternating episodes of microgravity, hypergravity and normal gravity. First, by isolating the effects of inertia in microgravity, we found that peak hand acceleration marked the transition between two modes of grip force control. Participants exerted grip forces that paralleled load force profiles, and then increased grip up to a maximum shifted after the collision. Second, we found that the oculomotor strategy adapted visual feedback of the controlled object around the collision, as demonstrated by longer durations of fixation after collision in new gravitational environments. Finally, despite large variability of arm dynamics in altered gravity, we found that saccades were remarkably time-locked to the peak hand acceleration in all conditions. In conclusion, altered gravity allowed light to be shed on predictive mechanisms used by the central nervous system to coordinate gaze, hand and grip motor actions during a mixed task that involved transport of an object and high impact loads.
Highlights
It is well established that eyes and hand are not independently controlled by the central nervous system in experimental contexts like pointing to targets [1,2], tracking [3], catching a real object [4] or intercepting a virtual ball [5,6]
There is an invariant relationship between the spatiotemporal characteristics of eye movements and limb kinematics in goaldirected movements: the end of a saccade toward a target corresponds temporally to the peak acceleration of the hand
We showed that the central nervous system does not try to predict the exact load force profile that occurs after impact; rather, it applies another predictive strategy consisting in gripping harder about 60 ms after the impact independently of the level of load force resulting from the collision [18]
Summary
It is well established that eyes and hand are not independently controlled by the central nervous system in experimental contexts like pointing to targets [1,2], tracking [3], catching a real object [4] or intercepting a virtual ball [5,6]. Pelz and collaborators explored the temporal coordination of eye, hand and head movements while subjects made a sequence of reaching movements to pick up and place blocks in the same configuration as a nearby model [15] They found that fixations gathered information about the patterns to be reproduced for subsequently guiding hand movements to pick up and place blocks. There is a growing body of work on eye-hand coordination, little is known about the role of gaze to control a hand-held object that contacts a stationary target
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