Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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BCCN Sonderseminar

Thursday, 06.09.2007 15 c.t.

A computational model for redundant human 3D pointing movements: Integration of independent spatial and temporal motor plans simplifies movement dynamics

by Dr. Armin Biess
from Weizmann Institute of Science, Rehovot, Israel

Contact person: Theo Geisel

Location

Seminarraum Haus 2, 4. Stock (Bunsenstr.)

Abstract

Few computational models have addressed the spatiotemporal features of unconstrained 3D arm motion. Empirical observations made on hand paths, speed profiles and arm postures during point-to-point movements led to the assumption that hand path and arm posture are independent of movement speed, suggesting that the geometric and temporal properties of movements are decoupled. In this talk I will present a computational model of 3D movements for a four degrees of freedom arm, based on the assumption that optimization principles are separately applied at the geometric and temporal levels of control. Geometric properties (path and posture) are defined in terms of geodesic paths in the Riemannian configuration space. Accordingly, a geodesic path can be generated with less muscular effort than on any other, non-geodesic path. The temporal properties of the movement (speed) are determined in task space by minimizing the squared-jerk along the selected end-effector path. The integration of both planning levels into a single spatiotemporal representation simplifies the control of arm dynamics along geodesic paths, and results in movements with near minimal torque-change and minimal peak-value of kinetic energy. Thus, the application of Riemannian geometry allows for a reconciliation of computational models previously proposed for the description of arm movements. The theoretical analysis is completed with experiments that validated the predictions for joint trajectories, hand paths, final postures, speed profiles and driving torques. This work was performed in collaboration with Dario G. Liebermann and Tamar Flash at the Weizmann Institute of Science.

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