SPACE-FLIGHT AND NEUROVESTIBULAR ADAPTATION

Space flight represents a form of sensory stimulus rearrangement requi ring modification of established terrestrial response patterns through central reinterpretation. Evidence of sensory reinterpretation is man ifested as postflight modifications of eye/head coordination, locomoto r patterns, postural control strategies, and illusory perceptions of s elf or surround motion in conjunction with head movements. Under norma l preflight conditions, the head is stabilized during locomotion, but immediately postflight reduced head stability, coupled with inappropri ate eye/head coordination, results in modifications of gait. Postfligh t postural control exhibits increased dependence on vision which compe nsates for inappropriate interpretation of otolith and proprioceptive inputs. Eye movements compensatory for perceived self motion, rather t han actual head movements have been observed postflight. Overall, the in-flight adaptive modification of head stabilization strategies, chan ges in head/eye coordination, illusionary motion, and postural control are maladaptive for a return to the terrestrial environment.