PRINCIPAL INVESTIGATOR (S ) : Jerry L. Horaick, Millard F. Reschke, and Earl F. 



Miller 



E XPERIMENT TITLE/NUMBER : The Effects of Prolonged Exposure to Weightlessness 



on Postural Equilibrium 



PROGRAM/MISSION : Skylab 2, 3, *» 



CLASSIFICATION : Human 



DISCIPLINE(S) : Neurosensory, Behavioral science 



OBJECTIVES : To assess the postural equilibrium of the Skylab astronauts 

 following their return to a 1-g environment and to suggest possible mechanisms 

 involved in any measured changes. 



PROTOCOL : Postural equilibrium was evaluated using a modified version of a 

 quantitative ataxia test developed by Graybiel and Fregley. The test employed 

 a series of narrow metal rails of varying widths on which the crewman was 

 required to maintain an upright position with his feet tandemly aligned and 

 arms folded across his chest. Performance for this test was measured under 

 two conditions. In the first test, the crewman kept his eyes open, and in the 

 second, he tried to balance with his eyes closed. In both cases, performance 

 was scored in terms of time on the rail before losing balance. Pref light 

 baseline data were obtained on three separate occasions for each of the 

 crewmen . 



EQUIPMENT : Postural test rails. 



RESULTS : There was a moderate postflight decrement in crewmen for the eyes 

 open test. The postflight decrement was considerable for the eyes closed test 

 which was most marked at R+1. Recovery was essentially complete at R+11. 



CONCLUSIONS : The data argue for an environment-dependent memory store of 

 frequently repeated sensory inputs that is under the guidance of a combined 

 otolith, kinesthetic, and touch system. It registers the actual movement and 

 allows for anticipation and compensation of each movement as it occurs. Being 

 environmentally dependent, such a mechanism could account for the buildup of 

 postural responses in zero-g that would be inappropriate upon return to one-g 

 reference. A mechanism of this type could be applied to account for sensory 

 physiological habituation in a variety of situations. In particular, such a 

 mechanism could provide an adequate basis for change when the acquired 

 response patterns are no longer congruent with the environment. 



PUBLICATIONS : 279, 280 



39 



