European vestibular experiments on the Spacelab-1 mission: 1. Overview.

During the flight of Spacelab-1 a series of vestibular experiments was performed on the crew by a group of European investigators. Control experiments were carried out on the same subjects pre- and postflight. The tests included caloric stimulation of the ears, threshold measurements of response to linear acceleration, motion sickness provocative stimuli, vestibulo-ocular reflexes during linear and angular stimulation, estimation of the subjective vertical (luminous line measurements) and static ocular counterrotation at various tilt angles. The caloric experiment proved the existence of a nonthermoconvective mechanism of caloric nystagmus in space. Most of the other test results point to a greater dependence on visual and somatosensory than on otolith cues in the microgravity environment. Some results, in particular the raised threshold to perception of linear acceleration in flight and the temporary reduction of ocular counterrotation at lateral tilts postflight, suggest a decreased gain of the otolith system as a possible effect of space vestibular adaptation.