HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 102/1/523    most recent 90948.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Laboissière, R. Articles by Ostry, D. J. PubMed PubMed Citation Articles by Laboissière, R. Articles by Ostry, D. J.

Impedance Control and Its Relation to Precision in Orofacial Movement

¹Institut National de la Santé et de la Recherche Médicale, U864, Espace et Action; ²Université Claude Bernard, Lyon 1, Institut Fédératif de Recherche des Neurosciences de Lyon, Institut Fédératif de Recherche sur le Handicap, Unité Mixte de Recherche S864, Bron, France; ³Max Planck Institute for Human Cognitive and Brain Sciences, Munich, Germany; ⁴Department of Psychology, McGill University, Montreal, Quebec, Canada; and ⁵Haskins Laboratories, New Haven, Connecticut

Submitted 21 August 2008; accepted in final form 4 May 2009

Speech production involves some of the most precise and finely timed patterns of human movement. Here, in the context of jaw movement in speech, we show that spatial precision in speech production is systematically associated with the regulation of impedance and in particular, with jaw stiffness—a measure of resistance to displacement. We estimated stiffness and also variability during movement using a robotic device to apply brief force pulses to the jaw. Estimates of stiffness were obtained using the perturbed position and force trajectory and an estimate of what the trajectory would be in the absence of load. We estimated this "reference trajectory" using a new technique based on Fourier analysis. A moving-average (MA) procedure was used to estimate stiffness by modeling restoring force as the moving average of previous jaw displacements. The stiffness matrix was obtained from the steady state of the MA model. We applied this technique to data from 31 subjects whose jaw movements were perturbed during speech utterances and kinematically matched nonspeech movements. We observed systematic differences in stiffness over the course of jaw-lowering and jaw-raising movements that were correlated with measures of kinematic variability. Jaw stiffness was high and variability was low early and late in the movement when the jaw was elevated. Stiffness was low and variability was high in the middle of movement when the jaw was lowered. Similar patterns were observed for speech and nonspeech conditions. The systematic relationship between stiffness and variability points to the idea that stiffness regulation is integral to the control of orofacial movement variability.