Motor adaptation to Coriolis force perturbations of reaching movements: endpoint but not trajectory adaptation transfers to the nonexposed arm

Abstract

1. Reaching movements made in a rotating room generate Coriolis forces that are directly proportional to the cross product of the room's angular velocity and the arm's linear velocity. Such Coriolis forces are inertial forces not involving mechanical contact with the arm. 2. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished at the onset of each reach. Prerotation subjects pointed with both the right and left arms in alternating sets of eight movements. During rotation at 10 rpm, the subjects reached only with the right arm. Postrotation, the subjects pointed with the left and right arms, starting with the left, in alternating sets of eight movements. 3. The initial perrotary reaching movements of the right arm were highly deviated both in movement path and endpoint relative to the prerotation reaches of the right arm. With additional movements, subjects rapidly regained straight movement paths and accurate endpoints despite the absence of visual or tactile feedback about reaching accuracy. The initial postrotation reaches of the left arm followed straight paths to the wrong endpoint. The initial postrotation reaches of the right arm had paths with mirror image curvature to the initial perrotation reaches of the right arm but went to the correct endpoint. 4. These observations are inconsistent with current equilibrium point models of movement control. Such theories predict accurate reaches under our experimental conditions. Our observations further show independent implementation of movement and posture, as evidenced by transfer of endpoint adaptation to the nonexposed arm without transfer of path adaptation. Endpoint control may occur at a relatively central stage that represents general constraints such as gravitoinertial force background or egocentric direction relative to both arms, and control of path may occur at a more peripheral stage that represents moments of inertia and muscle dynamics unique to each limb. 5. Endpoint and path adaptation occur despite the absence both of mechanical contact cues about the perturbing force and visual or tactile cues about movement accuracy. These findings point to the importance of muscle spindle signals, monitoring of motor commands, and possibly joint and tendon receptors in a detailed trajectory monitoring process. Muscle spindle primary and secondary afferent signals may differentially influence adaptation of movement shape and endpoint, respectively.

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.…”

“…However, when no haptic information was available, movements became straighter but were still inaccurate. In a subsequent study of interlimb transfer, DiZio and Lackner (1995) demonstrated that only final position information transferred to the nonexposed limb. This clearly suggests that trajectory and position seem to be differentially controlled.…”

“…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.…”

The role of kinematic redundancy in adaptation of reaching

“…Factors such as joint torques (or muscle force; Scheidt et al 2000), limb impedance (Takahashi et al 2001;Burdet et al 2001), and the relative contribution of feedforward and feedback mechanisms (Dizio and Lackner 1995;see also Bagesteiro and Sainburg 2005) likely play an important role in the adaptation process. Thus, our focus on the control of the hand trajectory will need to be extended in future work to account for the role of such factors in the adaptation process.…”

Specificity of Speech Motor Learning

“…The capacity for broad generalization seems to depend on multiple instances of local learning and a process of interpolation between individual examples (Atkeson, 1989;Gandolfo et al, 1996;Ghahramani and Wolpert, 1997;Malfait et al 2005;Mattar and Ostry, 2007a,b). Instances of generalization of dynamics learning have been described for interlimb movements, typically when movements, equivalent to those in the training condition, are repeated with the contralateral limb (Dizio and Lackner, 1995;CriscimagnaHemminger et al, 2003;Malfait and Ostry, 2004;Wang and Sainburg, 2004). Generalization for dynamics learning is also observed to movements that differ in amplitude and duration, but this is in the context of movements in a single direction (Goodbody and Wolpert, 1998).…”