Rapid adaptation to Coriolis force perturbations of arm trajectory

Abstract

1. Forward reaching movements made during body rotation generate tangential Coriolis forces that are proportional to the cross product of the angular velocity of rotation and the linear velocity of the arm. Coriolis forces are inertial forces that do not involve mechanical contact. Virtually no constant centrifugal forces will be present in the background when motion of the arm generates transient Coriolis forces if the radius of body rotation is small. 2. 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 prerotation, during rotation at 10 rpm in a fully enclosed rotating room, and postrotation. During testing the subject was seated at the center of the room and pointed radially. Neither visual nor tactile feedback about movement accuracy was present. 3. In experiment 1, subjects reached at a fast or slow rate and their hands made contact with a horizontal surface at the end of the reach. Their initial perrotary movements were highly significantly deviated relative to prerotation in both trajectories and end-points 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. Postrotation, 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. All subjects showed significant initial perrotation 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 postrotary movements. 5. These observations fail to support current equilibrium point models, both alpha and lambda, of movement control. Such theories would not predict endpoint errors under our experimental conditions, in which the Coriolis force is absent at the beginning and end of a movement. Our results indicate that detailed aspects of movement trajectory are 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 error. Moreover, movement trajectory and end-point can be remapped independently.(ABSTRACT TRUNCATED AT 400 WORDS)

Control of velocity and position in single joint movements

“…The idea that movement trajectory and final position are differentially controlled is also consistent with studies that have examined adaptation to novel forces (DiZio & Lackner, 1995;Lackner & DiZio, 1994) and visuomotor rotations (Sainburg & Wang, 2002;Wang & Sainburg, 2003. In the studies by Lackner and DiZio (DiZio & Lackner, 1995;Lackner & DiZio, 1994), participants reached to a target when adapting to Coriolis force fields, without any visual feedback.…”

“…In the studies by Lackner and DiZio (DiZio & Lackner, 1995;Lackner & DiZio, 1994), participants reached to a target when adapting to Coriolis force fields, without any visual feedback. When participants first experienced these forces, their handpaths were curved and inaccurate.…”

Motor learning through the combination of primitives

“…The cause of the discrepancy between these results and those of Lackner & Dizio (1994) has yet to be determined.…”

“…Another challenge to the equilibrium-point hypothesis comes from the work of Lackner & Dizio (1994) who asked subjects to execute reaching hand movements while sitting at the centre of a slowly rotating room. Because of this rotation, a Coriolis force proportional to the speed of the hand p erturbs the subject's arm.…”

Motions or muscles? Some behavioral factors underlying robotic assistance of motor recovery

“…The form of these movements is competently described as though they were chosen to be maximally smooth [44] in visually relevant coordinates: the path of the hand is straight and the speed profile has a single peak. Exposure to mechanical perturbations (such as motion-dependent force fields) that perturb this kinematic pattern evokes a spontaneous adaptation that restores the original pattern [45][46]. Conversely, exposure to visual displays that distort the appearance of the motion also evokes adaptation, again restoring the original kinematic pattern, even though that may require substantially different patterns of actual limb motion and muscle force [47][48].…”