Abstract
The centripetal force generated by a rotating space vehicle is a potential
source of artificial gravity. Minimizing the cost of such a vehicle
dictates using the smallest radius and highest rotation rate possible,
but head movements made at high rotation rates generate disorienting,
nauseogenic cross-coupled semicircular canal stimulation. Early studies
suggested 3 or 4 rpm as the highest rate at which humans could adapt
to this vestibular stimulus. These studies neglected the concomitant
Coriolis force actions on the headrneck system. We assessed non-vestibular
Coriolis effects by measuring arm and leg movements made in the 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 their
errors. Equilibrium point theories of motor control errantly predict
that Coriolis forces will not cause movement endpoint errors so that
subjects will not have to adapt their reaching movements during rotation.
Adaptation of movement trajectory acquired during Coriolis force
perturbations of one arm transfers to the unexposed arm but there
is no intermanual transfer of endpoint adaptation indicating that
neuromotor representations of movement endpoint and trajectory are
separable and can adapt independently, also contradictory to equilibrium
point theories. Touching a surface at the end of reaching movements
is required for complete endpoint adaptation in darkness but trajectory
adapts completely with or without terminal contact. We have also
made the first kinematic measurements of unconstrained head movements
during rotation, these movements show rapid adaptation to Coriolis
force perturbations. Our results point to methods for achieving full
compensation for rotation up to 10 rpm.
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