Extending Kohonen’s Self-Organizing Mapping Algorithm to Learn Ballistic Movements

Abstract

Rapid limb movements are known to be initiated by a brief torque pulse at the joints and to proceed freely thereafter (ballistic movements). To initiate such movements with a desired starting velocity u requires knowledge of the relation between torque pulse and desired velocity of the limb. We show for a planar two-link arm model that this relationship can be learnt with the aid of a self-organizing mapping of the type proposed earlier by Kohonen. To this end we extend Kohonen’s algorithm by a suitable learning rule for the individual units and show that this approach results in a significant improvement in the convergency properties of the learning rule used.