Spatial orientation and posture during and following weightlessness: human experiments on Spacelab Life Sciences 1.

The 4 payload crew members of the Spacelab Life Sciences 9-day space flight in 1991 were subjected to limited vestibular testing in flight as well as pre and post flight. Major differences in individual "perceptual style" appeared in their reaction to the visual-vestibular stimuli in the rotating dome experiment, and especially in the extent to which nondirectional tactile cues served to anchor the subjective vertical and body postural reactions. The ability of subjects to point to remembered target positions was degraded in space, which produced a tendency to point low in some subjects in flight. The eye movements and subjective response to sudden stops and head pitching following continuous spinning (dumping) were measured both in space and on the ground. Although subjective duration of inflight rotation for the dumping tests was shorter than that for the preflight tests, the postrotatory nystagmus, with or without head pitch, was lengthened in time constant relative to preflight. Ground tests, in addition to the flight experiments, investigated the changes following weightlessness in subjective and oculomotor reactions to whole body tilt, the ability to balance with eyes open and closed; leg muscles strength and stamina as related to posture; visual field dependence; and the perceptual and oculomotor reactions to horizontal linear acceleration. Several of these tests, as well as post-flight measures of motion sickness susceptibility, revealed subtle evidence of neurovestibular alterations that lasted a week or more following the 10-day orbital exposure.