Summary and Conclusions:

1. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished as movement began. The reaching movements were made pre-rotation, during rotation at 10 rpm in a fully enclosed rotating room, and post rotation. The subject was seated at the center of the room and pointed radially.

2. Reaching movements made during rotation generate tangential Coriolis forces that were the cross product of the angular velocity of rotation and the radial velocity of the arm. Coriolis forces are inertial forces that do not involve mechanical contact.

3. In experiment 1, subjects reached at a fast or slow rate and their hands made terminal contact with a surface at the end of the reach. Their initial per-rotary movements were highly significantly deviated, relative to pre-rotation in both trajectories and endpoints in the direction of the transient Coriolis forces that had been generated during the reaches. Despite the absence of visual and tactile feedback about reaching accuracy, all subjects rapidly regained straight movement trajectories and accurate endpoints. Post-rotation transient errors of opposite sign were present for both trajectories and endpoints.

4. In a second experiment, the conditions were identical except that subjects pointed just above the location of the extinguished target so that no surface contact was involved. The subjects showed significant initial per-rotation deviations of trajectories and endpoints in the direction of the transient Coriolis forces. With repeated reaches the trajectories, as viewed from above, again became straight but there was only partial restoration of endpoint accuracy so that subjects reached in a straight line to the wrong place. Aftereffects of opposite sign were transiently present in the post-rotary movements.

5. These observations fail to support current equilibrium point models, both and , of movement control. Such theories would not predict endpoint errors under our experimental conditions. Our results point to detailed aspects of movement trajectory being continuously monitored on the basis of proprioceptive feedback in relation to motor commands. Adaptive compensations can be initiated after one perturbation despite the absence of either visual or tactile feedback about movement trajectory and endpoint errors. Movement trajectory and endpoint can be remapped independently.

6. We interpret these results as emphasizing that movement trajectory and endpoint are continuously monitored. A model showing how this might be done is presented, it shows how proprioceptive, motor, and somato-sensory factors could be used in updating movement control and compensating for changes in limb inertia and dynamics.

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