Rosemary A. Lester

Physiologic and acoustic patterns of essential vocal tremor.

OBJECTIVES/HYPOTHESIS This article describes a case study of physiologic and acoustic patterns of essential vocal tremor (EVT). Simulations of vocal tremor were used to test hypotheses regarding measured acoustic patterns and expected physiologic sources. STUDY DESIGN This is a case study of EVT using an analysis by synthesis approach. METHODS Oscillations of vocal tract and laryngeal structures were identified using rigid videostroboscopic examination. Acoustical analyses of sustained phonation were completed using the methods previously described in the literature and custom-written MATLAB functions. Simulations of the clients vocal tremor were created using a computational model. RESULTS The client exhibited vocal fold length changes and oscillation within the laryngeal vestibule during sustained phonation at a comfortable pitch and loudness. Despite the involvement of vocal fold length changes, a low average extent of fundamental frequency (F0) modulation (ie, 5.3%) and high average extent of intensity modulation (ie, 23.0%) were measured. Simulations of vocal tremor involving modulation of F0 demonstrated that this source of tremor contributes to frequency-induced intensity modulation, although there was a greater extent of F0 modulation than intensity modulation. CONCLUSIONS The greater extent of intensity than F0 modulation in one client with EVT exhibiting predominant vocal fold length changes contrasted with the lower extent of intensity than F0 modulation in simulated vocal tremor involving F0 modulation. These findings demonstrate that other potential sources of intensity modulation outside the larynx should be determined during the evaluation of clients with vocal tremor.

The Clinicopathologic Spectrum of Benign Mass Lesions of the Vocal Fold due to Vocal Abuse

Benign masses of the vocal fold related to phonotrauma are clinically classified into polyps, nodules, Reinke’s edema, and cysts. Despite the apparent distinctiveness of the clinical nomenclature, low inter- and intraobserver diagnostic agreement has been reported. Excepting cysts, which are epithelial lined, histologic examination of the remaining lesions has shown a variety of overlapping features insufficiently specific for the clinical diagnoses. This study reviews the clinicopathologic characteristics among these benign lesions of the vocal fold. A total of 78 nonneoplastic lesions of the vocal fold were reviewed by 2 pathologists for the presence of epithelial hyperplasia, basement membrane thickening, edema, vascular proliferation, and extracellular “amyloid-like” fibrin. In 46 cases with prebiopsy stroboscopic images, 2 otolaryngologists classified each lesion as polyp, nodule, Reinke’s edema, cyst, or other. They agreed in 43% (n = 20, 13 polyps, 5 nodules, 1 Reinke’s edema, 1 other) and disagreed in 57% (n = 26). There was no histologic feature that reliably distinguished among the lesions. In addition, reactive stromal cell atypia was present in 14 cases. Cysts were distinctive, as all were epithelial lined. The clinicopathologic classification of benign laryngeal lesions is neither clinically reproducible nor histologically unique. Treatment will continue to be individualized based on clinical judgment.

Distinguishing intrinsic from extrinsic factors underlying firing rate saturation in human motor units

During voluntary contraction, firing rates of individual motor units (MUs) increase modestly over a narrow force range beyond which little additional increase in firing rate is seen. Such saturation of MU discharge may be a consequence of extrinsic factors that limit net synaptic excitation acting on motor neurons (MNs) or may be due to intrinsic properties of the MNs. Two sets of experiments involving recording of human biceps brachii MUs were carried out to evaluate saturation. In the first set, the extent of saturation was quantified for 136 low-threshold MUs during isometric ramp contractions. Firing rate-force data were best fit by a saturating function for 90% of MUs recorded with a maximum rate of 14.8 ± 2.0 impulses/s. In the second set of experiments, to distinguish extrinsic from intrinsic factors underlying saturation, we artificially augmented descending excitatory drive to biceps MNs by activation of muscle spindle afferents through tendon vibration. We examined the change in firing rate caused by tendon vibration in 96 MUs that were voluntarily activated at rates below and at saturation. Vibration had little effect on the discharge of MUs that were firing at saturation frequencies but strongly increased firing rates of the same units when active at lower frequencies. These results indicate that saturation is likely caused by intrinsic mechanisms that prevent further increases in firing rate in the presence of increasing synaptic excitation. Possible intrinsic cellular mechanisms that limit firing rates of motor units during voluntary effort are discussed.

Discriminating Simulated Vocal Tremor Source Using Amplitude Modulation Spectra

OBJECTIVES/HYPOTHESIS Sources of vocal tremor are difficult to categorize perceptually and acoustically. This article describes a preliminary attempt to discriminate vocal tremor sources through the use of spectral measures of the amplitude envelope. The hypothesis is that different vocal tremor sources are associated with distinct patterns of acoustic amplitude modulations. STUDY DESIGN Statistical categorization methods (discriminant function analysis) were used to discriminate signals from simulated vocal tremor with different sources using only acoustic measures derived from the amplitude envelopes. METHODS Simulations of vocal tremor were created by modulating parameters of a vocal fold model corresponding to oscillations of respiratory driving pressure (respiratory tremor), degree of vocal fold adduction (adductory tremor), and fundamental frequency of vocal fold vibration (F0 tremor). The acoustic measures were based on spectral analyses of the amplitude envelope computed across the entire signal and within select frequency bands. RESULTS The signals could be categorized (with accuracy well above chance) in terms of the simulated tremor source using only measures of the amplitude envelope spectrum even when multiple sources of tremor were included. CONCLUSIONS These results supply initial support for an amplitude-envelope-based approach to identify the source of vocal tremor and provide further evidence for the rich information about talker characteristics present in the temporal structure of the amplitude envelope.

Acoustical bases for the perception of simulated laryngeal vocal tremor

Vocal tremor involves atypical modulation of the fundamental frequency (F0) and intensity of the voice. Previous research on vocal tremor has focused on measuring the modulation rate and extent of the F0 and intensity without characterizing other modulations present in the acoustic signal (i.e., modulation of the harmonics). Characteristics of the voice source and vocal tract filter are known to affect the amplitude of the harmonics and could potentially be manipulated to reduce the perception of vocal tremor. The purpose of this study was to determine the adjustments that could be made to the voice source or vocal tract filter to alter the acoustic output and reduce the perception of modulation. This research was carried out using a computational model of speech production that allows for precise control and modulation of the glottal and vocal tract configurations. Results revealed that listeners perceived a higher magnitude of voice modulation when simulated samples had a higher mean F0, greater degree ...

Nasal and Oral Inspiration During Natural Speech Breathing

PURPOSE The purpose of this study was to determine the typical pattern for inspiration during speech breathing in healthy adults, as well as the factors that might influence it. METHOD Ten healthy adults, 18–45 years of age, performed a variety of speaking tasks while nasal ram pressure, audio, and video recordings were obtained. Inspirations were categorized as nasal-only, oral-only, simultaneous nasal and oral, or alternating nasal and oral inspiration. The method was validated using nasal airflow, oral airflow, audio, and video recordings for 2 participants. RESULTS The predominant pattern was simultaneous nasal and oral inspirations for all speaking tasks. This pattern was not affected either by the nature of the speaking task or by the phonetic context surrounding the inspiration. The validation procedure confirmed that nearly all inspirations during counting and paragraph reading were simultaneous nasal and oral inspirations, whereas for sentence reading, the predominant pattern was alternating nasal and oral inspirations across the 3 phonetic contexts. CONCLUSIONS Healthy adults inspire through both the nose and mouth during natural speech breathing. This pattern of inspiration is likely beneficial in reducing pathway resistance while preserving some of the benefits of nasal breathing.

Discriminating vocal tremor source from amplitude envelope modulations

Vocal tremor can have a variety of physiological sources. For example, tremors can result from involuntary oscillation of respiratory muscles (respiratory tremor), or of the muscles responsible for vocal fold adduction (adductory tremor) or lengthening (f0 tremor). While the sources of vocal tremor are distinct, they are notoriously difficult to categorize both perceptually and acoustically. In order to develop acoustic measures that can potentially distinguish sources of tremor, speech samples were synthesized using a kinematic model of the vocal folds attached to a model of the vocal tract and trachea [Titze, JASA, 75, 570-580; Story, 2005, JASA, 117, 3231-3254]. Tremors were created by modulating parameters of the vocal fold model corresponding to the three types mentioned above. The acoustic measures were related to temporal regularities in the amplitude envelope computed across the entire signal and select frequency bands. These measures could reliably categorize the samples by tremor source (as dete...