Novel strategies in feedforward adaptation to a position-dependent perturbation

Hinder, MR and Milner, TE (2005) Novel strategies in feedforward adaptation to a position-dependent perturbation. Experimental Brain Research, 165 2: 239-249. doi:10.1007/s00221-005-2294-x

Author Hinder, MR
Milner, TE
Title Novel strategies in feedforward adaptation to a position-dependent perturbation
Journal name Experimental Brain Research   Check publisher's open access policy
ISSN 0014-4819
Publication date 2005
Sub-type Article (original research)
DOI 10.1007/s00221-005-2294-x
Volume 165
Issue 2
Start page 239
End page 249
Total pages 11
Editor R.F. Schmidt
V.J. Wilson
Place of publication New York
Publisher Springer
Collection year 2005
Language eng
Subject C1
321403 Motor Control
780108 Behavioural and cognitive sciences
1109 Neurosciences
1702 Cognitive Sciences
Abstract To investigate the control mechanisms used in adapting to position-dependent forces, subjects performed 150 horizontal reaching movements over 25 cm in the presence of a position-dependent parabolic force field (PF). The PF acted only over the first 10 cm of the movement. On every fifth trial, a virtual mechanical guide (double wall) constrained subjects to move along a straight-line path between the start and target positions. Its purpose was to register lateral force to track formation of an internal model of the force field, and to look for evidence of possible alternative adaptive strategies. The force field produced a force to the right, which initially caused subjects to deviate in that direction. They reacted by producing deviations to the left, into the force field, as early as the second trial. Further adaptation resulted in rapid exponential reduction of kinematic error in the latter portion of the movement, where the greatest perturbation to the handpath was initially observed, whereas there was little modification of the handpath in the region where the PF was active. Significant force directed to counteract the PF was measured on the first guided trial, and was modified during the first half of the learning set. The total force impulse in the region of the PF increased throughout the learning trials, but it always remained less than that produced by the PF. The force profile did not resemble a mirror image of the PF in that it tended to be more trapezoidal than parabolic in shape. As in previous studies of force-field adaptation, we found that changes in muscle activation involved a general increase in the activity of all muscles, which increased arm stiffness, and selectively-greater increases in the activation of muscles which counteracted the PF. With training, activation was exponentially reduced, albeit more slowly than kinematic error. Progressive changes in kinematics and EMG occurred predominantly in the region of the workspace beyond the force field. We suggest that constraints on muscle mechanics limit the ability of the central nervous system to employ an inverse dynamics model to nullify impulse-like forces by generating mirror-image forces. Consequently, subjects adopted a strategy of slightly overcompensating for the first half of the force field, then allowing the force field to push them in the opposite direction. Muscle activity patterns in the region beyond the boundary of the force field were subsequently adjusted because of the relatively-slow response of the second-order mechanics of muscle impedance to the force impulse.
Keyword Neurosciences
Motor Learning
Internal Dynamics Model
Human Arm Stiffness
Unstable Dynamics
Impedance Control
Multijoint Movement
Muscle Activation
Motor Adaptation
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2006 Higher Education Research Data Collection
School of Human Movement and Nutrition Sciences Publications
Version Filter Type
Citation counts: TR Web of Science Citation Count  Cited 8 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 9 times in Scopus Article | Citations
Google Scholar Search Google Scholar
Created: Wed, 15 Aug 2007, 05:57:18 EST