GRAVITOINERTIAL FORCE BACKGROUND LEVEL AFFECTS ADAPTATION TO CORIOLIS-FORCE PERTURBATIONS NF REACHING MOVEMENTS

We evaluated the combined effects on reaching movements of the transie nt, movement-dependent Coriolis forces and the static centrifugal forc es generated in a rotating environment. Specifically, we assessed the effects of comparable Coriolis force perturbations in different static force backgrounds. Two groups of subjects made reaching movements tow ard a just-extinguished visual target before rotation began, during 10 rpm counterclockwise rotation, and after rotation ceased. One group w as seated on the axis of rotation, the other 2.23 m away. The resultan t of gravity and centrifugal force on the hand was 1.0 g for the on-ce nter group during 10 rpm rotation, and 1.031 g for the off-center grou p because of the 0.25 g centrifugal force present. For both groups, ri ghtward Coriolis forces, approximate to 0.2 g peak, were generated dur ing voluntary arm movements. The endpoints and paths of the initial pe r-rotation movements were deviated rightward for both groups by compar able amounts. Within 10 subsequent reaches, the on-center group regain ed baseline accuracy and straight-line paths; however, even after 40 m ovements the off-center group had not resumed baseline endpoint accura cy. Mirror-image aftereffects occurred when rotation stopped. These fi ndings demonstrate that manual control is disrupted by transient Corio lis force perturbations and that adaptation can occur even in the abse nce of visual feedback. An increase, even a small one, in background f orce level above normal gravity does not affect the size of the reachi ng errors induced by Coriolis forces nor does it affect the rate of re acquiring straight reaching paths; however, it does hinder restoration of reaching accuracy.