Laboissière Rafael, Lametti Daniel R, Ostry David J
Institut National de la Santé et de la Recherche Médicale, U864, Espace et Action, Lyon, France.
J Neurophysiol. 2009 Jul;102(1):523-31. doi: 10.1152/jn.90948.2008. Epub 2009 May 6.
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.
言语产生涉及一些人类运动中最精确且时间安排最精细的模式。在此，在言语中下颌运动的背景下，我们表明言语产生中的空间精度与阻抗调节系统地相关，特别是与下颌刚度相关——下颌刚度是对位移阻力的一种度量。我们使用一个机器人设备向下颌施加短暂的力脉冲来估计运动过程中的刚度以及变异性。刚度估计是通过使用受扰位置和力轨迹以及在无负载情况下轨迹的估计值来获得的。我们使用一种基于傅里叶分析的新技术来估计这个“参考轨迹”。使用移动平均（MA）程序通过将恢复力建模为先前下颌位移的移动平均来估计刚度。刚度矩阵是从MA模型的稳态获得的。我们将此技术应用于31名受试者的数据，这些受试者在言语发声过程中下颌运动受到扰动，以及在运动学上匹配的非言语运动。我们观察到在降下颌和升下颌运动过程中刚度存在系统差异，这些差异与运动学变异性的度量相关。当下颌抬起时，运动早期和晚期下颌刚度高且变异性低。当下颌降低时，运动中间刚度低且变异性高。在言语和非言语条件下观察到类似的模式。刚度和变异性之间的系统关系表明刚度调节是口面部运动变异性控制所不可或缺的。
