Abstract
The success of many space missions critically depends on human capabilities and performance. Yet, it is known that sensorimotor performance is degraded under conditions of weightlessness. Therefore, astronauts prepare for their missions in simulated weightlessness under water. In the present study, we investigated sensorimotor performance in simulated weightlessness (induced by shallow water immersion) and whether performance can be improved by choosing appropriate haptic settings of the human–machine interface (e.g., motion damping). Twenty-two participants performed basic aiming and tracking tasks with a force feedback joystick under water and on land and with different haptic settings of the joystick (no haptics, three spring stiffnesses, and two motion dampings). While higher resistive forces should be avoided for rapid aiming tasks in simulated weightlessness, tracking performance is best with higher motions damping in both land and water setups, although the performance losses due to water immersion cannot be compensated. The overall result pattern also provides insights into the causal mechanism behind the slowing effect during aiming motions and decreased accuracy of tracking motions in simulated weightlessness. Findings provide evidence that distorted proprioception due to altered muscle spindle activity seemingly is the main trigger of impaired sensorimotor performance in simulated weightlessness.
Highlights
During their space missions, astronauts have to perform delicate and demanding tasks reliably and precisely, under the adverse conditions of weightlessness
Consistent with research on microgravity during spaceflight, we found similar effects when performing aiming and tracking tasks during shallow water immersion
The present study provides evidence that planning complex multi-limb motions against resistive forces and the execution of highly accurate aiming and tracking motions are more demanding in simulated weightlessness
Summary
Astronauts have to perform delicate and demanding tasks reliably and precisely, under the adverse conditions of weightlessness. Repeatedly documented that human motor performance in weightlessness is degraded under certain conditions (Lackner and DiZio 2000; Manzey 2017). Three main explanations have been proposed for these sensorimotor impairments in weightlessness: (1) distorted proprioception due to altered muscle spindle activity, e.g., Bock (1998), (2) attentional deficits due to the general workload of space missions, e.g., Manzey et al (2000), and (3) altered motor control strategy to avoid instability of the weightless body during limb movements, e.g., Mechtcheriakov et al (2002). For instance, usually have a spring mechanism to stabilize deflections and support re-centering. Studies showed that moderate values of stiffness improve tracking as well as precision aiming performance
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