Eric Muller

Strain gauge transduction of lip and jaw motion in the midsagittal plane: Refinement of a prototype system

This paper describes the design refinements made in an earlier prototype system for transducing lip and jaw movements in the midsagittal plane. Major improvements over the prototype system included: reduced transducer loading, improved two-dimensional separation and resolution, elimination of possible artifacts due to lateral-medial or rotational movement, electrical isolation of the subject from the transducer, increased capability to transduce movements of children as well as adults, and an accessory instrument for orienting the transducers with reference to defined anatomical planes.

Perioral biomechanics and its relation to labial motor control

Data summarizing the biomechanical nature of the labial system will be presented. The following topics will be discussed: the transfer function of the perioral tissue; spectral analysis of muscle fatigue; isometric and isotonic analysis of the contractal properties of muscle Obicularis Oris (mOO); and the describing function relating EMG and the contractile dynamics of mOO. The data will be discussed with regard to their implications for motor control of the labial system of speech production. [Research supported by NINCDS grant.]

Higher-order oligomerization of Spc110p drives γ-tubulin ring complex assembly

Assembly of the microtubule-nucleating γ-tubulin ring complex (γTuRC) requires higher-order oligomerization of Spc110p, which connects γTuRC to the yeast spindle pole body (SPB). Because Spc110p is highly concentrated at the SPB, spatial regulation of microtubule nucleation is thus achieved by exclusive assembly of γTuRCs proximal to the SPB.

Spc110 N-Terminal Domains Act Independently to Mediate Stable γ-Tubulin Small Complex Binding and γ-Tubulin Ring Complex Assembly

Microtubule (MT) nucleation in vivo is regulated by the γ-tubulin ring complex (γTuRC), an approximately 2-megadalton complex conserved from yeast to humans. In Saccharomyces cerevisiae, γTuRC assembly is a key point of regulation over the MT cytoskeleton. Budding yeast γTuRC is composed of seven γ-tubulin small complex (γTuSC) subassemblies which associate helically to form a template from which microtubules grow. This assembly process requires higher-order oligomers of the coiled-coil protein Spc110 to bind multiple γTuSCs, thereby stabilizing the otherwise low-affinity interface between γTuSCs. While Spc110 oligomerization is critical, its N-terminal domain (NTD) also plays a role that is poorly understood both functionally and structurally. In this work, we sought a mechanistic understanding of Spc110 NTD using a combination of structural and biochemical analyses. Through crosslinking-mass spectrometry (XL-MS), we determined that a segment of Spc110 coiled-coil is a major point of contact with γTuSC. We determined the structure of this coiled-coil segment by X-ray crystallography and used it in combination with our XL-MS dataset to generate an integrative structural model of the γTuSC-Spc110 complex. This structural model, in combination with biochemical analyses of Spc110 heterodimers lacking one NTD, suggests that the two NTDs within an Spc110 dimer act independently, one stabilizing association between Spc110 and γTuSC and the other stabilizing the interface between adjacent γTuSCs.

Vocal tract area functions from autoregressive analysis of two‐point acoustic data

It is well known that the frequencies of the low‐order driving point impedance poles and zeros of the vocal tract can be used to determine a smoothed representation of the vocal tract area function. The impedance poles are congruent with the vocal tract formants; the pole frequencies are specified by the location of peaks in the speech spectrogram. The impedance zero frequencies are indirectly related to formant bandwidths. The bandwidths, however, are difficult to accurately measure from speech. A method is presented for estimating vocal tract impedance zero frequencies directly as the peaks of the transfer function relating the acoustic speech signal to the acceleration signal from a transducer taped to the skin of the neck at the thyroid notch. This transfer function is estimated from pressure and acceleration signals using an autoregressive technique. Area function reconstructions derived from estimated pole and zero frequencies from human speech are presented. [Work supported by NIH.]

Analytic methods in the articulatory interpretation of the aero‐dynamic events accompanying consonant production

The utility of a biophysically based model of consonant aerodynamics has been shown to be a considerable heuristic tool in the articulatory interpretation of the oral pressure and air flow events accompanying consonant production. Our current modeling work in this area has expanded into a number of diverse, though complementary, directions. Topics to be discussed include sensitivity analysis, the inclusion of stochastic processes in the model, hypotheses concerning an optimal adaptive controller, and the application of the model to the evaluation of dysarthric speech. While these avenues of inquiry may represent significant analytic inroads for understanding speech production, they are at best limited, as the nature of the speech motor control process cannot be elucidated by analysis of a limited aspect of the “speech chain” and without regard to performance criteria. Thus we conclude that systems modeling, on a global level will become an increasingly important aspect of speech research. [Research suppor...

Magnitude of perioral reflexes as a function of stimulus velocity and isometric lip force

A quantitative description of peripheral nervous‐system function may enhance our ability to analyze speech motor control. With respect to lip motor control, recent evidence [R. Netsell and J. Abbs, J. Acoust. Soc. Am. 58, S41 (1975)] suggests that perioral reflexes may be actively modulated throughout lip movement for speech. In the present study, factors explored to clarify the manner in which these reflexes may be modulated during control of lip movement. Previous studies of perioral reflexes have been handicapped by the inability to systematically vary the characteristics of the mechanical simulus. The present investigation utilized an electromagnet under displacement sensitive servo control, coupled to a force transduction system, which delivered mechanical stimuli of different velocities against the lip of normal adult subjects. Reflexes were recorded from hooked‐wire EMG electrodes inserted into the orbicularis oris muscle while the lip was either passive or exerting an isometric force. Perioral ref...