Article

It was proposed to investigate whether the central nervous system is able to
select the most appropriate reference frame for controlling subjects' vertical
orientation in response to severe environmental constraints such as microgravity
and support perturbations. The question addressed was whether the subjects,
regardless of their perceptual typology, might be able to use the same visual
reference frame to control their vertical orientation. Fifteen subjects were
asked to perform a sit-to-stand (STS) task under microgravity. Subjects were
seated on a chair with their feet fixed to a horizontal or forwards tilted
support (20 degrees ). When the support was tilted the subjects' ankles were
placed at an angle of 110 degrees . Two main findings emerged from this study.
First, in all the experimental conditions, the results obtained showed that the
subjects' controlled their postural orientation fairly correctly but not very
precisely, since a bias was systematically observed in their head and trunk
orientation. In other words, changes in their ankle angles and the absence of
gravity only slightly disturbed their vertical body orientation, and when these
two constraints were applied concomitantly, their effects were not cumulative.
Secondly, contrary to our initial hypothesis, the subjects' postural orientation
performances were not correlated with the perceptual typology. All the subjects
preferentially used the visual reference frame to control their vertical postural
orientation. The present findings confirm that the proprioceptive dominance of
visual independent (VI) subjects enhances their ability to select the most
appropriate reference frame to deal with inter-sensory disturbances such as those
consisting here of microgravity combined with proprioceptive perturbations
imposed at ankle level.
CI - Copyright (c) 2010 Elsevier B.V. All rights reserved.

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