[Abstract Title]. - Society for Neuroscience

Program#/Poster#: 275.22/KK3
Topic: D.16.d. Kinematics and Muscle Activity
Support: The Wellcome Trust
The Whitaker Foundation
The European SENSOPAC Project (IST-2005-028056)
Title: Generalization of dynamic learning for posture and movement
Authors: *A. A. AHMED, D. M. WOLPERT;
Engin., Univ. Cambridge, Cambridge, United Kingdom
Abstract: Skillful movement depends upon our ability to predict the consequences that our
actions have on our bodies and environment. It is widely accepted that this predictive control
relies on a central representation (internal model) of the internal and external dynamics.
However, it is not known whether learning novel dynamics of the arm in a seated position will
generalize to the same movement performed while standing. In addition, will the postural system
be able to generalize to standing and predict and compensate for the destabilizing consequences
of these dynamics on posture?
Initially, seated subjects made reaching movements to targets in the horizontal plane while
grasping the handle of a robotic, force-generating, manipulandum. Their reaching movements
were perturbed with a force proportional to their movement velocity, but perpendicular in
direction. Following the seated trials, subjects stood on a force plate and performed another set
of reaching movements in the presence of the force perturbations. Handle position, robotgenerated
forces, and forceplate forces were recorded at 500 Hz. To assess learning of the
dynamics in both the seated and standing conditions, we examined movement error on each trial.
Quality of learning was assessed with random catch trials, where hand movement was restricted
to a path along the target vector, using a force channel. Feedforward control of posture in the
standing position was measured as the position and velocity of the center of pressure at the onset
of hand movement. Movement of the center of pressure in the direction of the impending
perturbing force indicates anticipatory control.
All participants learned to make relatively accurate reaching movements to the target while
seated, and significantly reduced their movement error. Upon switching to a standing posture,
hand error remained reduced. Similarly, by the end of the sitting phase, participants generated
significant anticipatory forces on catch trials and this performance was maintained upon
changing to a standing posture. However, on standing subjects did not initially compensate for
the postural perturbation in an anticipatory manner and generated similar postural responses as
found when reaching in the absence of a force field. Over the course of several trials,
anticipatory postural responses developed. These findings indicate that learned dynamics of the
arm generalizes from sitting to standing but that the postural system does not generalize
anticipatory mechanisms between body postures.
Disclosures: A.A. Ahmed, None; D.M. Wolpert, None.