Does the motor control system use multiple models and context switching to cope with a variable environment?

Abstract

Studies of arm movements have shown that subjects learn to compensate predictable mechanical perturbations by developing a representation of the relation between the state of motion of the arm and the perturbing forces. Here, we tested the hypothesis that subjects construct internal representations of two different force fields and switch between them when presented with an alternating sequence of these fields. Our results do not support this hypothesis. Subjects performed reaching movements in four sessions over 4 days. On the 1st day the robotic manipulandum perturbed the movement by perpendicular force that alternated its direction after each movement. Subjects were unable to construct the two underlying models and switch between them. On the 2nd day only one field was applied and well learned. On the 3rd day only the other field was applied and well learned. Then the experiment of the 1st day was repeated on the 4th day. Even after this extensive training subjects showed no signs of improved performance with alternating fields. This result combined with previous studies suggests that the central nervous system has a strong tendency to employ a single internal model when dealing with a sequence of perturbations.

Visual Cues Signaling Object Grasp Reduce Interference in Motor Learning

“…How interference occurs is not entirely clear, although previous studies have put forward a number of ideas (Bock 2003;Brashers-Krug et al 1996;Caithness et al 2004;Gandolfo et al 1996;Karniel and Mussa-Ivaldi 2002;Krakauer and Shadmehr 2006;Krakauer et al 2005;Magill and Hall 1990;Mattar and Ostry 2007;Overduin et al 2006;Shadmehr and BrashersKrug 1997;Tong and Flanagan 2003;Tong et al 2002;Wada et al 2003). Motor learning entails learning to predict the consequences of movement, in this case, forming progressively more accurate predictions of how a mechanical environment like a force field affects movement (Brashers-Krug et al 1996;Conditt et al 1997;Shadmehr and Mussa-Ivaldi 1994;Thoroughman and Shadmehr 1999).…”

Generalization of Motor Learning Based on Multiple Field Exposures and Local Adaptation

“…The ability to learn and retain the properties of several different environments has been offered as evidence of a modular structure to motor learning (Doya et al 2002;Flanagan et al 1999;Ghahramani and Wolpert 1997;Haruno et al 2001;Karniel and Mussa-Ivaldi 2002;Kawato 1999;. As an example, Ghahramani and Wolpert (1997) examined adaptation to opposite visual perturbations that were applied during movements from two different starting locations.…”

Visuomotor adaptation to a visual rotation is gravity dependent

“…The progressive modification of the actual horizontal temporal pattern toward a vertical pattern was not followed by any consistent aftereffects, which usually highlight an adaptation process (Karniel et al 2002;Shadmehr and Mussa-Ivaldi 1994). In other words, the spontaneous recovery when conflict was removed did not reflect the adaptation rate: the participants adapted slowly and deadapted immediately.…”