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Self-selected modular recurrent neural networks with postural and inertial subnetworks applied to complex movements
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Self-selected modular recurrent neural networks with postural and inertial subnetworks applied to complex movements
Jean-Philippe Draye1, Jack M. Winters2 and Guy Cheron3
| (1) |
Avaya Belgium sa/nv, Waterloo Office Park, Building K, Drève Richelle 161, 1410 Waterloo, Belgium, BE |
| (2) |
Biomedical Engineering Department, Catholic University of America, Washington, D.C., USA, US |
| (3) |
Laboratory of Biomechanics, University of Brussels, Brussels, Belgium, BE |
Abstract. It has been shown that dynamic recurrent neural networks are successful in identifying the complex mapping relationship between
full-wave-rectified electromyographic (EMG) signals and limb trajectories during complex movements. These connectionist models
include two types of adaptive parameters: the interconnection weights between the units and the time constants associated
to each neuron-like unit; they are governed by continuous-time equations. Due to their internal structure, these models are
particularly appropriate to solve dynamical tasks (with time-varying input and output signals). We show in this paper that
the introduction of a modular organization dedicated to different aspects of the dynamical mapping including privileged communication
channels can refine the architecture of these recurrent networks. We first divide the initial individual network into two
communicating subnetworks. These two modules receive the same EMG signals as input but are involved in different identification
tasks related to position and acceleration. We then show that the introduction of an artificial distance in the model (using
a Gaussian modulation factor of weights) induces a reduced modular architecture based on a self-elimination of null synaptic
weights. Moreover, this self-selected reduced model based on two subnetworks performs the identification task better than
the original single network while using fewer free parameters (better learning curve and better identification quality). We
also show that this modular network exhibits several features that can be considered as biologically plausible after the learning
process: self-selection of a specific inhibitory communicating path between both subnetworks after the learning process, appearance
of tonic and phasic neurons, and coherent distribution of the values of the time constants within each subnetwork.
Received: 17 September 2001 / Accepted in revised form: 15 January 2002
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