Effects of Vocal Training and Phonatory Task on Voice Onset Time

OBJECTIVES/HYPOTHESIS: The purpose of this study was to examine the temporal-acoustic differences between trained singers and nonsingers during speech and singing tasks. METHODS: Thirty male participants were separated into two groups of 15 according to level of vocal training (ie, trained or untrained). The participants spoke and sang carrier phrases containing English voiced and voiceless bilabial stops, and voice onset time (VOT) was measured for the stop consonant productions. RESULTS: Mixed analyses of variance revealed a significant main effect between speech and singing for /p/ and /b/, with VOT durations longer during speech than singing for /p/, and the opposite true for /b/. Furthermore, a significant phonatory task by vocal training interaction was observed for /p/ productions. CONCLUSIONS: The results indicated that the type of phonatory task influences VOT and that these influences are most obvious in trained singers secondary to the articulatory and phonatory adjustments learned during vocal training.     

Voice Analysis of Postlingually Deaf Adults Pre- and Postcochlear Implantation

Objectives

To ascertain whether cochlear implantation (CI), without specific vocal rehabilitation, is associated with changes in perceptual and acoustic vocal parameters in adults with severe to profound postlingual deafness.

Hypothesis

Merely restoring auditory feedback could allow the individual to make necessary adjustments in vocal pattern.

Study Design

Prospective and longitudinal.

Methods

The experimental group composed of 40 postlingually deaf adults (20 males and 20 females) with no previous laryngeal or voice disorders. Participants’ voices were recorded before CI and 6–9 months after CI. To check for chance modifications between two evaluations, a control group of 12 postlingually deaf adults, six male and six female, without CI was also evaluated. All sessions composed of the recording of read sentences from Consensus Auditory-Perceptual Evaluation of Voice and sustained vowel /a/. Auditory and acoustic analyses were then conducted.

Results

We found a statistically significant reduction in overall severity, strain, loudness, and instability in auditory analysis. In vocal acoustic analysis, we found statistically significant reduction fundamental frequency (F0) values (in male participants) and F0 variability (in both genders). The control group showed no statistically significant changes in most vocal parameters assessed, apart from pitch and F0 (in female participants only). On comparing the interval of variation of results between the experimental and control groups, we found no statistically significant difference in vocal parameters between CI recipients and nonrecipients, with the exception of F0 variability in male participants.

Conclusions

The patients in our sample showed changes in overall severity, strain, loudness, and instability values, and reductions in F0 and its variability. On comparing the variation of results between the groups, we were able to prove in our study that implant recipients postlingually deaf adults (experimental group), without specific vocal rehabilitation, differed from nonrecipients (control group) in loudness and F0 variability sustained vowel /a/ in male participants.     

Vocal Tract Configurations in Male Alto Register Functions

Purpose

Professional male altos (countertenors) mostly use a register function, which is considered to be derived from falsetto. However, the sound produced differs in professional altos compared with the modal register or falsetto of untrained voices. The aim of this study was to analyze differences of the vocal tract shapes in male alto register functions.

Material and Methods

Dynamic real-time magnetic resonance imaging of eight frames per second was used to analyze the vocal tract profile in seven professional male altos who sang on the vowel /a/, an ascending and descending scale from G3 (196 Hz) to E4 (330 Hz). The scale included their register transition from modal register to stage (counter) falsetto and naïve falsetto.

Results

Register transitions from modal register to stage falsetto were associated with increased lip opening, jaw retraction, elevation and back positioning of the tongue, pharynx narrowing, uvula elevation, drop of larynx height, and tilting of the larynx. Differences between stage and naïve falsetto were found mostly with regard to lip opening and pharynx width.

Conclusions

The differences between the vocal tract configurations might have an impact on the acoustic characteristics observed in professional male alto register functions.     

Voice and Laryngeal Configuration of Men With Unilateral Vocal Fold Paralysis Before and After Medialization

Aim

To describe the laryngeal configuration and the voice of male patients diagnosed with unilateral vocal fold paralysis (UVFP) before and after medialization.

Methods

A retrospective study involving the collection of data from medical records of 142 patients diagnosed with UVFP from January 2003 to April 2009, submitted to auditory-perceptual assessment of voices and visual perception of laryngeal images before and after medialization.

Results

The study included data from 24 male patients, with an average of 60.7 years, who underwent three surgical medialization techniques (injection of hyaluronic acid, type I thyroplasty, and injection of Teflon). Before treatment, the position of the paralyzed vocal fold was seen to have a significant influence to the passing of the healthy vocal fold beyond the midline and on the overall degree of dysphonia. After treatment, the complete glottic closure; the free margin of the linear vocal fold; paralyzed vocal fold in the median position, reduction of hoarseness, roughness and breathiness (more frequently mild), and asthenia (more frequently normal and mild); tension and instability (more frequency normal); and a decrease in the overall degree of dysphonia were found to be significant.

Conclusion

The position of the paralyzed vocal fold influences the position of the healthy vocal fold in relation to the midline and the overall degree of dysphonia. All three treatments improved the glottic configuration and the voice of patients with UVFP.     

Differences in Self-Rated, Perceived, and Acoustic Voice Qualities Between High- and Low-Fatigue Groups

Objectives

The present study was performed to examine which factors among self-rated scales, perceptual evaluations, and acoustic parameters, calculated from sustained vowels, are reliable indicators of physical and mental fatigues.

Methods

A total of 73 volunteers (male:female, 52:21), aged 19–24 years, were enrolled in this study. We defined the high- and low-fatigue groups using the Chalder Fatigue Scale score. For assessment of self-rated symptoms, each subject was asked to complete Voice Handicap Index (VHI) and Voice Rating Scale (VRS). For perceptual evaluations, three clinicians assessed each subject’s vocal quality on the Grade, Roughness, Breathiness, Asthenia, Strain Scale. For acoustic analysis, each subject was asked to produce sustained vowels /a/, /e/, /i/, /o/, and /u/ for 3 seconds. Then, the habitual fundamental frequency (F₀), jitter, shimmer, F₀ tremor, mean F₀, standard deviation of F₀, maximum F₀, minimum F₀, normalized noise energy, harmonic-to-noise ratio (HNR), signal-to-noise ratio (SNR), amplitude tremor, and ratio within 2–4 kHz were calculated using Dr. Speech software.

Results

In men, VHI, VRS, F₀ tremor, shimmer, HNR, SNR, and amplitude tremor were related to mental fatigue. In women, only VHI was related to physical fatigue, and none of the acoustic parameters was related to the fatigue score. Perceptual evaluations were not related to fatigue in men or women.

Conclusions

These findings suggest that self-rated symptoms and acoustic parameters related to voice quality are indicative of mental fatigue, and these features are prominent in men.     

Allograft (Alloderm) and Autograft (Temporalis Fascia) Implantation for Glottic Insufficiency: A Novel Approach

Objective

Traditionally, glottic insufficiency because of scar, atrophy, and sulcus has been treated by injection or medialization laryngoplasty. These procedures do not reestablish the vertical height of the vocal fold margin. We propose soft tissue augmentation laryngoplasty with allograft (sheet Alloderm; LifeCell Corporation, Branchburg, NJ) or autograft (temporalis fascia) via a minithyrotomy or a transoral approach.

Study Design

A retrospective case series analysis of 21 patients treated by sheet Alloderm or temporalis fascia for correction of glottic insufficiency.

Methods

Twenty-one patients with glottic insufficiency secondary to scar, atrophy, or sulcus were treated. Ten failed prior techniques. Seventeen had minithyrotomy by a small fenestration in the thyroid cartilage. Exploration of scar or lamina propria through the fenestration allowed for the creation of a pocket for Alloderm implantation within the intermediate layer of the lamina propria. Four patients underwent a transoral approach by cordotomy with either Alloderm or temporalis fascia implantation, which also allowed for exploration of scar but required repair using sutures. These implantation approaches allowed for both restoration of the layered structure and augmentation of the middle third of the musculomembranous vocal fold. Preoperative and postoperative videostroboscopic examinations were reviewed with review of clinical outcome.

Results

With a median follow-up time of 12 months, patients demonstrated excellent long-term vocal fold augmentation and minimal absorption of the implant in 19 out of 21 patients. There is improved pliability of the vocal fold with good oscillation in scar patients.

Conclusion

Minithyrotomy with soft tissue augmentation is a novel approach for soft tissue augmentation of glottic insufficiency. It has the advantage of augmentation of the medial edge of the vocal fold with a soft tissue implant that has long-term viability. Its role should be explored further in patients with atrophy and scar.     

Characteristics of Phonatory Function in Singers and Nonsingers With Vocal Fold Nodules

Purpose

The goals of this study were to determine if there were significant differences between singers and nonsingers in the morphology of vocal nodules and the associated impact on vocal function.

Method

Participants were 10 professionally trained singers with nodules, eight nonsingers with nodules, and 10 individuals with healthy normal voice (controls). Surface electromyography (sEMG) from three anterior neck locations and acoustic rise times for vowels /a/ and /i/ were measured in all the participants. In individuals with nodules, dB SPL/cm H₂O, glottal airflow, and nodule location and size were also measured.

Results

There were no significant differences between singers and nonsingers with nodules in terms of airflow, dB SPL/cm H₂O, nodule size, or nodule location. In nonsingers with nodules, airflow and nodule size were significantly correlated, but were not significantly correlated in singers. Vowel rise times and sEMG during vocal tasks did not differentiate among nodule and control groups. Sternocleidomastoid sEMG during initiation of the vowel /a/ was statistically significantly stronger in nonsingers with nodules relative to singers with nodules and controls.

Conclusions

Nodule morphology did not differ between singers and nonsingers, although some behavioral aspects of phonation differed between the groups.     

Vowel Harmonic Amplitude Differences in Persons With Vocal Nodules

Background

Spectrum is a fast Fourier transform-generated power spectrum extracted from the speech sample. It is reported to provide a quantitative acoustic index of the degree of glottal abduction and adduction in voices perceived to be breathy or pressed. In the present study, it was hypothesized that there would be abnormal reduction of higher harmonic amplitudes relative to the amplitude of the first harmonics in the subjects with vocal nodules and hence the present study was carried out.

Method

One hundred twenty participants were divided into clinical group and control group. They were instructed to phonate /a/ at their most comfortable pitch and loudness. Fourier transformation of the recorded acoustic signal was first performed to create a spectrum. Amplitudes were measured for the first and second harmonics (H1 and H2) as well as the harmonics at the first, second, and third formants (A1, A2, and A3) using the Computerized Speech Science Lab (Kay Pentax, Lincoln, NJ).

Results

There was a significant difference between the means of two groups for all the parameters, such as H1-H2, H1-A1, H1-A2, and H1-A3 at P < 0.05. The obtained results are discussed with respect to the underlying pathophysiology.

Conclusions

The present study investigated the vowel harmonic amplitude differences in persons with vocal nodules. The results revealed a significant difference between the two groups for the vowel harmonic amplitude differences. This particular measure could be used to track the changes following the vocal treatment.     

Consonant and vowel confusions in speech-weighted noise

This paper presents the results of a closed-set recognition task for 64 consonant-vowel sounds (16 C X 4 V, spoken by 18 talkers) in speech-weighted noise (-22,-20,-16,-10,-2 [dB]) and in quiet. The confusion matrices were generated using responses of a homogeneous set of ten listeners and the confusions were analyzed using a graphical method. In speech-weighted noise the consonants separate into three sets: a low-scoring set C1 (/f/, /theta/, /v/, /d/, /b/, /m/), a high-scoring set C2 (/t/, /s/, /z/, /S/, /Z/) and set C3 (/n/, /p/, /g/, /k/, /d/) with intermediate scores. The perceptual consonant groups are C1: {/f/-/theta/, /b/-/v/-/d/, /theta/-/d/}, C2: {/s/-/z/, /S/-/Z/}, and C3: /m/-/n/, while the perceptual vowel groups are /a/-/ae/ and /epsilon/-/iota/. The exponential articulation index (AI) model for consonant score works for 12 of the 16 consonants, using a refined expression of the AI. Finally, a comparison with past work shows that white noise masks the consonants more uniformly than speech-weighted noise, and shows that the AI, because it can account for the differences in noise spectra, is a better measure than the wideband signal-to-noise ratio for modeling and comparing the scores with different noise maskers.     

Bacterial Cellulose as Laryngeal Medialization Material: An Experimental Study

Hypothesis

The use of a material made of bacterial cellulose with the aim of obtaining vocal fold medialization has not hitherto been fully investigated. Although the material has been tested in other animal models, the evaluation did not include the larynx; hence, situations, such as tissue reaction, material absorption, and extrusion, need to be addressed to evaluate its usefulness as a material for laryngeal reconstruction.

Objective

To evaluate the medialization, tissue response, and healing of rabbit vocal folds, after the implantation of a membrane of bacterial cellulose.

Study Design

Experimental study.

Methods

A total of 32 rabbits were used, two of which were used to check out the adequacy of the implant location. The animals were followed for 4 months and grouped according to follow-up times of 2, 4, and 16 weeks. All test animals received an implant of bacterial cellulose in one vocal fold and the injection of distilled water in the other, both performed by videoendoscopic cervicotomy. At the end of the follow-up, the presence of inflammatory and medial displacement was evaluated.

Results

No statistically significant difference in the inflammatory parameters between the study and control vocal folds or among follow-up times was found. All animals receiving cellulose presented medial displacement of vocal folds, and all retained this material at the implant site up to study endpoint.

Conclusion

Bacterial cellulose is a useful material for laryngeal medialization, showing no signs of rejection or absorption.     

On the relation between the dimensions and resonance characteristics of the vocal tract: a study with MRI.

The relation between the spatial configuration of the vocal tract as determined by magnetic resonance imaging (MRI) and the acoustical signal produced was investigated. A male subject carried out a set of phonatory tasks, comprising the utterance of the sustained vowels /i/ and /a/, each in a single articulation, and the vowel /epsilon/ with his larynx positioned variously on a vertical axis. Two- and three-dimensional measurements of the vocal tract were performed. The results of these measurements were used to calculate resonance frequencies, according to predictions from acoustical theory. Finally, calculated frequencies were compared with actually measured resonance frequencies in the audio signal. We found a strong relation between the acoustical signal produced and the spatial configuration for the first resonance frequencies of the articulations of the vowel /epsilon/, and first two resonance frequencies of the vowels /a/ and /i/. The capability to determine accurately vocal tract dimensions is a major advantage of this imaging technique.     

Maximum Phonation Time in Healthy Older Adults

Objectives/Hypothesis

Maximum phonation time (MPT), a clinical measurement of the longest time one can phonate a vowel, typically /a/, is a frequently used measure of vocal function, but normative data are lacking for MPT in healthy older adults. The aim of this study was to provide data on MPT in healthy older adults and to determine the effect of advanced age, gender, and repeated measures on MPT.

Study Design

Prospective.

Methods

Sixty-nine healthy older adult volunteers participated (ie, 15, 26, and 28 in the seventh, eighth, and ninth decades of life, respectively). The effects of age, gender, and repeated measures (three trials in a single session) on MPT were assessed. Mean, standard deviation, compound symmetry covariance, analysis of variance, and analysis of covariance were used for statistical analysis.

Results

Neither age group, gender, trial, nor their interactions was statistically significant (P > 0.05). Adults in the seventh, eighth, and ninth decades of life had mean MPTs of 22.27 (standard error [SE] = 1.56), 22.97 (SE = 1.11), and 21.14 (SE = 0.97) seconds, respectively. Females and males had mean MPTs of 20.96 (SE = 0.92) and 23.23 (SE = 0.96) seconds, respectively. Finally, MPTs for trials 1, 2, and 3 were 21.77 (SE = 1.09), 21.67 (SE = 1.12), and 22.80 (SE = 1.27), respectively.

Conclusions

MPTs were longer in this group of older adults than previously reported and did not vary significantly with age or gender. Additionally, across a single short sampling session, measurements were relatively stable across three trials of MPTs.     

Accuracy and variability of acoustic measures of voicing onset

Five commonly used methods for determining the onset of voicing of syllable-initial stop consonants were compared. The speech and glottal activity of 16 native speakers of Cantonese with normal voice quality were investigated during the production of consonant vowel (CV) syllables in Cantonese. Syllables consisted of the initial consonants /ph/, /th/, /kh/, /p/, /t/, and /k/ followed by the vowel /a/. All syllables had a high level tone, and were all real words in Cantonese. Measurements of voicing onset were made based on the onset of periodicity in the acoustic waveform, and on spectrographic measures of the onset of a voicing bar (f0), the onset of the first formant (F1), second formant (F2), and third formant (F3). These measurements were then compared against the onset of glottal opening as determined by electroglottography. Both accuracy and variability of each measure were calculated. Results suggest that the presence of aspiration in a syllable decreased the accuracy and increased the variability of spectrogram-based measurements, but did not strongly affect measurements made from the acoustic waveform. Overall, the acoustic waveform provided the most accurate estimate of voicing onset; measurements made from the amplitude waveform were also the least variable of the five measures. These results can be explained as a consequence of differences in spectral tilt of the voicing source in breathy versus modal phonation.     

Effects of consonant manner and vowel height on intraoral pressure and articulatory contact at voicing offset and onset for voiceless obstruents

In obstruent consonants, a major constriction in the upper vocal tract yields an increase in intraoral pressure (P(io)). Phonation requires that subglottal pressure (P(sub)) exceed P(io) by a threshold value, so as the transglottal pressure reaches the threshold, phonation will cease. This work investigates how P(io) levels at phonation offset and onset vary before and after different German voiceless obstruents (stop, fricative, affricates, clusters), and with following high vs low vowels. Articulatory contacts, measured using electropalatography, were recorded simultaneously with P(io) to clarify how supraglottal constrictions affect P(io). Effects of consonant type on phonation thresholds could be explained mainly in terms of the magnitude and timing of vocal-fold abduction. Phonation offset occurred at lower values of P(io) before fricative-initial sequences than stop-initial sequences, and onset occurred at higher levels of P(io) following the unaspirated stops of clusters compared to fricatives, affricates, and aspirated stops. The vowel effects were somewhat surprising: High vowels had an inhibitory effect at voicing offset (phonation ceasing at lower values of P(io)) in short-duration consonant sequences, but a facilitating effect on phonation onset that was consistent across consonantal contexts. The vowel influences appear to reflect a combination of vocal-fold characteristics and vocal-tract impedance.     

Multiparametric Analysis of Vocal Fold Vibrations in Healthy and Disordered Voices in High-Speed Imaging

Objectives

The aim of this study was to look for visual subjective and objective parameters of vocal fold dynamics being capable of differentiating healthy from pathologic voices in daily clinical practice applying endoscopic high-speed digital imaging (HSI).

Study Design and Methods

Four hundred ninety-six datasets containing 80 healthy and 416 pathologic subjects (232 functional dysphonia (FD), 13 bilateral, and 171 unilateral vocal fold nerve paralysis) were analyzed retrospectively. Videos at 4000 Hz (256 × 256 pixel) were recorded during sustained phonation. Subjective parameters were visually evaluated and complemented by an analysis of objective parameters. Visual subjective parameters were mucosal wave, glottal closure type, glottal closure insufficiency (GI), asymmetries of the vocal folds, and phonovibrogram (PVG) symmetry. After image segmentation, objective parameters were computed: closed quotient, perturbation measures (PMs) of glottal area, and left-right asymmetry values.

Results

HSI evaluation enabled to distinguish healthy from pathologic voices. For visual subjective parameters, GI, symmetrical behavior, and PVG symmetry exhibited statistical significant differences. For 95% of the data, objective parameters could be computed. Among objective parameters, closed quotient, jitter, shimmer, harmonic-to-noise ratio, and signal-to-noise ratio for the glottal area function differentiated statistically significant normal from pathologic voices. Applying linear discriminant analysis by combining visual subjective and objective parameters, accurate classifications were made for 63.2% of the female and 87.5% of the male group for the three-class problem (healthy, FD, and unilateral vocal fold nerve paralysis).

Conclusion

Actual acoustically applied PMs can be transferred to clinical beneficial HSI analysis. Combining visual subjective and objective basic parameters succeeds in differentiating pathologic from healthy voices. The presented evaluation can easily be included into everyday clinical practice. However, further research is needed to broaden our understanding of the variability within and across healthy and pathologic vocal fold vibrations for diagnosing voice disorders and therapy control.     

Velopharyngeal aerodynamics of /m/ and /p/ in tracheoesophageal speech

The purpose of this study was to compare oral pressure (P_o), nasal airflow (V_n), and velopharyngeal (VP) orifice area estimates from 12 tracheoesophageal (TE) and 12 laryngeal speakers as they produced /p/ and /m/ in syllable series. The findings were as follows: (1) TE speakers produced greater P_o than the laryngeal speakers; (2) for /p/, TE speakers generated V_n, and VP orifice area estimates comparable with, or less than, the laryngeal speakers; and (3) for /m/, TE speakers had V_n and VP orifice area estimates greater than the laryngeal speakers. The elevated P_o could be the result of several factors such as high source driving pressures and vocal tract volume changes postlaryngectomy. Attempts at more precise articulation, and subsequently less coarticulation, by the TE speakers may explain the V_n and VP orifice area estimates for /p/ and /m/. TE speakers may be limiting the oral-nasal cavity coupling for /p/ (smaller VP gap, less V_n) in an attempt to produce a very precise oral /p/. For /m/, TE speakers may be attempting to overtly mark the consonant as a nasal (greater V_n, larger VP gap). Further studies are needed to confirm/refute the explanations postulated here regarding the VP aerodynamic differences that were identified.     

Physiological aspects of a vocal exercise

The physiological aim of vocal exercises is mostly understood in intuitive terms only. This article presents an attempt to document the phonatory behavior induced by a vocal exercise. An elevated vertical position of the larynx is frequently associated with hyperfunctional phonatory habits, presumably because it induces an exaggerated vocal fold adduction. Using the multichannel electroglottograph (MEGG), the laryngeal position was determined in a group of subjects who performed a voice exercise that contained extremely prolonged versions of the consonant /b:/. This exercise is used by the coauthor (N.E.) as part of a standard vocal exercise program. Two of the seven subjects were dysphonic phonastenic patients, and the rest were normal trained or untrained persons. Different attempts to calibrate the MEGG confirmed a linear relationship with larynx height, provided electrode positioning was correct. The results showed that the exercise induced substantial vertical displacements of the larynx. Comparison with larynx height during voicing of other consonants showed that the /b/, in particular, tended to lower the larynx.     

Pattern of BOLD signal in auditory cortex relates acoustic response to perceptual streaming

Background

The ultrasonic vocalizations (USV) of courting male mice are known to possess a phonetic structure with a complex combination of several syllables. The genetic mechanisms underlying the syllable sequence organization were investigated.

Results

This study compared syllable sequence organization in two inbred strains of mice, 129S4/SvJae (129) and C57BL6J (B6), and demonstrated that they possessed two mutually exclusive phenotypes. The 129S4/SvJae (129) strain frequently exhibited a "chevron-wave" USV pattern, which was characterized by the repetition of chevron-type syllables. The C57BL/6J strain produced a "staccato" USV pattern, which was characterized by the repetition of short-type syllables. An F1 strain obtained by crossing the 129S4/SvJae and C57BL/6J strains produced only the staccato phenotype. The chevron-wave and staccato phenotypes reappeared in the F2 generations, following the Mendelian law of independent assortment.

Conclusions

These results suggest that two genetic loci control the organization of syllable sequences. These loci were occupied by the staccato and chevron-wave alleles in the B6 and 129 mouse strains, respectively. Recombination of these alleles might lead to the diversity of USV patterns produced by mice.     

The Role of the Cricothyroid Joint Anatomy in Cricothyroid Approximation Surgery

Objectives/Hypothesis

Cricothyroid approximation (CTA) surgery aims at raising the voice pitch in male-to-female transsexuals. However, 30% of the patients are not satisfied with the result. The purpose of our study was to examine the cricothyroid joint (CTJ) biomechanics and to analyze if (and how) the CTJ anatomy influences the movement of the cricoid and, consequently, the elongation of the vocal fold and the voice pitch after CTA.

Methods

Twenty-four cadaver larynges were examined with high-resolution computerized tomography and MIMICS three-dimensional imaging software (Materialise Interactive Medical Image Control System, Leuven, Belgium). After superimposing the two scans taken in “neutral” and in “CTA” positions, vector geometrical analysis was used to determine the effective rotation axis of the CTJ and to calculate the elongation of the vocal folds after CTA.

Results

Our results showed that the cricoid rotates around an axis, the position of which depends on the anatomical structure of the CTJ. Based on the location of this effective rotation axis, we could distinguish three groups. In group I (N = 13), the rotation axis was located in the lower third; in group II (N = 5), it was located in the middle third; and in group III (N = 6), it was located in the upper third of the cricoid. The elongations of the vocal fold were 12%, 8%, and 3%, in groups I, II, and III, respectively.

Conclusions

The anatomical structure of the CTJ influences directly (1) the position of the effective rotation axis and (2) the elongation of the vocal folds.     

Temporal measures of anticipatory labial coarticulation for the vowel/u/: within- and cross-subject variability.

The timing of upper lip protrusion movements and accompanying acoustic events was examined for multiple repetitions of word pairs such as "lee coot" and "leaked coot" by four speakers of American English. The duration of the intervocalic consonant string was manipulated by using various combinations of /s/, /t/, /k/, /h/, and /#/. Pairwise comparisons were made of consonant string duration (acoustic /i/ offset to acoustic /u/ onset) with durations of: protrusion movement beginning to acoustic /u/ onset, maximum acceleration of the movement to acoustic /u/ onset, and acoustic /u/ onset to movement end. There were some consonant-specific protrusion effects, primarily on the movement beginning event for /s/. Inferences from measures of the maximum acceleration and movement end events for the non-/s/ subset suggested the simultaneous and variable expression of three competing constraints: (1) end the protrusion movement during the voiced part of the /u/; (2) use a preferred movement duration; and (3) begin the /u/-related protrusion movement when permitted by relaxation of the perceptually motivated constraint that the preceding /i/ be unrounded. The subjects differed in the degree of expression of each constraint, but the results generally indicate that anticipatory coarticulation of lip protrusion is influenced both by acoustic-phonetic context dependencies and dynamical properties of movements. Because of the extensive variation in the data and the small number of subjects, these ideas are tentative; additional work is needed to explore them further.