Egocentric references and human spatial orientation in microgravity

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Abstract
This article describes the results of the “ellipses” experiment conducted during the second French-Soviet spaceflight (project Aragatz). The realization of oriented motor tasks, on the basis of internal body representation and without visual feedback, was chosen as a paradigm for studying the determinants of spatial orientation under weightlessness. The process of drawing ellipses in the air, using arm movements with axes parallel or perpendicular to the longitudinal body axis, was studied under normal gravity and in weightlessness, and recorded using a video computer motion-analyzing system (Kinesigraph). On Earth, the experiments were performed in standing and lying positions, and in flight, in the erect position with the feet fixed to the floor. In general, performance of the task in microgravity was not disturbed. Under conditions of spaceflight, the longitudinal ellipse was inclined forward in accordance with the inclination of the whole body relative to the fixed feet. On Earth, the angle between the long axes of longitudinal and transverse ellipses deviated from 90° by 20–30°. The same deviation persisted under microgravity conditions. The distinctive features of ellipses traced by individual subjects were also preserved. It is concluded that an egocentric reference system ensures normal performance of sensorimotor tasks in the absence of a gravitational reference.