Synthesis of V-V sequences with a 2D biomechanical tongue model controlled by the Equilibrium Point Hypothesis

Yohan Payan,Pascal Perrier

doi:10.1016/s0167-6393(97)00019-8

Abstract

An assessment of a target-based control model of speech production using Feldman's Equilibrium Point Hypothesis is presented. It consists of simulations of articulatory movements during Vowel-to-Vowel sequences with a 2D biomechanical tongue model. In the model the main muscles responsible for tongue movements and tongue shaping in the mid-sagittal plane are represented. The elastic properties are accounted through a Finite-Element modeling, while force generation principles are implemented according to the non-linear force-length Invariant Characteristics proposed by Feldman. Movement is produced through control variable shifts at rates that are constant throughout each transition. The external contours of the model are adjusted to approximate X-ray data collected on a native speaker of French, and it is inserted in the vocal tract contours of the speaker. Thus, from tongue shapes generated with the model, it was possible to produce formant trajectories compatible with the speaker's acoustic space. It permitted a comparison of simulations with real data collected on the speaker in the kinematic and acoustic domains. Emphasis is put on the realism of synthesized formant trajectories, and on the potential influence of biomechanical tongue properties on to measurable kinematic features.

Highlights

Interesting insights into speech control have been provided from studies based on analyses of articula tory and/or acoustic signals (Munhall et al, 1985; Nittrouer et al, 1988; Sock and Lofqvist, 1995)
The control of the model was based on Feldman's ( 1966) Equilib rium Point Hypothesis (EPH), which proposes that limb movements are produced by centrally specified shifts of the mechanical equilibrium of the peripheral motor system
This paper presents simulations obtained with an original 2D biomechanical model of the tongue, whose control is based on the same principles

Summary

Introduction

Interesting insights into speech control have been provided from studies based on analyses of articula tory and/or acoustic signals (Munhall et al, 1985; Nittrouer et al, 1988; Sock and Lofqvist, 1995). The physical speech signals are, the consequence of the interaction between the mechanical structure of the articulatory apparatus and the forces that act on it. This interaction will be referred to as dynamics in the paper. The control of the model was based on Feldman's ( 1966) Equilib rium Point Hypothesis (EPH), which proposes that limb movements are produced by centrally specified shifts of the mechanical equilibrium of the peripheral motor system (see similar results obtained with a biomechanical jaw model in Perrier et al, 1996b)

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