ADAPTATION IN A ROTATING ARTIFICIAL GRAVITY ENVIRONMENT

The centripetal force generated by a rotating space vehicle is a poten tial source of artificial gravity. Minimizing the cost of such a vehic le dictates using the smallest radius and highest rotation rate possib le, but head movements made at high rotation rates generate disorienti ng, nauseogenic cross-coupled semicircular canal stimulation. Early st udies suggested 3 or 4 rpm as the highest rate at which humans could a dapt to this vestibular stimulus. These studies neglected the concomit ant Coriolis force actions on the head/neck system. We assessed non-ve stibular Coriolis effects by measuring arm and leg movements made in t he center of a rotating room turning at 10 rpm and found that movement endpoints and trajectories are initially deviated; however, subjects readily adapt with 10-20 additional movements, even without seeing the ir errors. Equilibrium point theories of motor control errantly predic t that Coriolis forces will not cause movement endpoint errors so that subjects will not have to adapt their reaching movements during rotat ion. Adaptation of movement trajectory acquired during Coriolis force perturbations of one arm transfers to the unexposed arm but there is n o intermanual transfer of endpoint adaptation indicating that neuromot or representations of movement endpoint and trajectory are separable a nd can adapt independently, also contradictory to equilibrium point th eories. Touching a surface at the end of reaching movements is require d for complete endpoint adaptation in darkness but trajectory adapts c ompletely with or without terminal contact. We have also made the firs t kinematic measurements of unconstrained head movements during rotati on, these movements show rapid adaptation to Coriolis force perturbati ons. Our results point to methods for achieving full compensation for rotation up to 10 rpm. (C) 1998 Published by Elsevier Science B.V. All rights reserved.