Mechanisms of larynx and vocal fold development and pathogenesis.

The larynx and vocal folds sit at the crossroad between digestive and respiratory tracts and fulfill multiple functions related to breathing, protection and phonation. They develop at the head and trunk interface through a sequence of morphogenetic events that require precise temporo-spatial coordination. We are beginning to understand some of the molecular and cellular mechanisms that underlie critical processes such as specification of the laryngeal field, epithelial lamina formation and recanalization as well as the development and differentiation of mesenchymal cell populations. Nevertheless, many gaps remain in our knowledge, the filling of which is essential for understanding congenital laryngeal disorders and the evaluation and treatment approaches in human patients. This review highlights recent advances in our understanding of the laryngeal embryogenesis. Proposed genes and signaling pathways that are critical for the laryngeal development have a potential to be harnessed in the field of regenerative medicine.

The development of the cricoid cartilage and its implications for the use of endotracheal tubes in the pediatric population.

BACKGROUND: The rigid cricoid cartilage is functionally the narrowest portion of the larynx. There is some controversy over the shape of the pediatric cricoid cartilage in the transverse plane. It is important to understand the development of the cricoid cartilage so that endo-traceheal tubes can be used more safely. AIM: To determine changes in the internal diameter and shape of the cricoid cartilage during development and explore the implications of those changes for the selection of ETT type and size for children. METHODS: The cervical computed tomography scans were reviewed in patients aged 1-20 years. After performing the multiplanar reconstruction and correcting the slant, the transverse and anteroposterior internal diameters of the inlet and outlet of the cricoid cartilage were measured, respectively. The angle between the arch and the lamina of the cricoid cartilage in the middle sagittal plane was measured. The ratios of transverse to anteroposterior diameter for the inlet and outlet of the cricoid cartilage were calculated, respectively. RESULTS: In females, the internal diameters of the cricoid cartilage increased linearly with age. In males, the internal diameters of the cricoid cartilage exhibited a growth spurt during adolescence. The transverse diameter of the inlet was the smallest diameter of the cricoid cartilage, and the predicting formula of the transverse diameter of the inlet for children aged 1-12 was 0.4 × age (year) + 5.1, R2  = .758. The angle between the arch and lamina of the cricoid cartilage and the ratios of transverse to anteroposterior diameter correlated weakly with age. CONCLUSION: The transverse inner diameter of the inlet is the smallest diameter of the cricoid cartilage. The "funnel shape" of the cricoid cartilage remains unchanged during development. The outer diameter should be considered when selecting an endotracheal tube.

Consideration of Cough Reflex Development When Ordering Modified Barium Swallow Studies in Infants.

Infants < 51 weeks post-menstrual age (< 51 PMA) are often referred for modified barium swallow (MBS) studies for suspected silent aspiration (SA) given a possible association between SA and aspiration pneumonia. Infants this young are unlikely to have developed a mature laryngeal cough reflex, most likely rendering SA an expected finding in those who aspirate. The aims of this retrospective review were to (1) determine if SA resolves in a significant proportion of infants around the expected emergence of the laryngeal cough reflex, (2) determine which factors or characteristics are associated with and without SA resolution in these infants, and (3) determine if SA, or any aspiration, is associated with increased rates of lower respiratory infection (including aspiration pneumonia) in these infants. Results from the chart review revealed that 79/148 (53.4%) infants had SA on MBS < 51 PMA. 16/48 (33.3%) infants assessed for SA by the time of the expected emergence of the cough reflex had resolution. SA resolution was less common in infants with obstructive sleep apnea (p = 0.037). A total of 50/70 (71.4%) infants with a follow-up MBS had eventual SA resolution. Aspiration was not significantly associated with LRI, including aspiration pneumonia. The results suggested that the laryngeal cough reflex might develop later than reported in the literature and there is no association between aspiration and LRI. These findings may indicate that age should be considered before ordering an MBS solely to assess for SA in this population. The study provides preliminary evidence for future prospective research regarding SA resolution.

The anatomy of the pediatric airway: Has our knowledge changed in 120 years? A review of historic and recent investigations of the anatomy of the pediatric larynx.

BACKGROUND: There is disagreement regarding the anatomy of the pediatric airway, particularly regarding the shape of the cricoid cartilage and the location of the narrowest portion of the larynx. AIMS: The aim of this review is to clarify the origin and the science behind these differing views. METHODS: We undertook a review of published literature, University Libraries, and authoritative textbooks with key search words and phrases. RESULTS: In vivo observations suggest that the narrowest portion of the airway is more proximal than the cricoid cartilage. However, in vitro studies of autopsy specimens measured with rods or calipers, confirm that the nondistensible and circular or near circular cricoid outlet is the narrowest level. These anatomic studies confirmed the classic "funnel" shape of the pediatric larynx. In vivo studies are potentially misleading as the aryepiglottic, vestibular, and true vocal folds are in constant motion with respiration. These studies also do not consider the effects of normal sleep, inhalation agents, and comorbidities such as adenoid or tonsil hypertrophy that cause some degree of pharyngeal collapse and alter the normal movement of the laryngeal tissues. Thus, the radiologic studies suggesting that the narrowest portion of the airway is not the cricoid cartilage may be the result of an artifact depending upon which phase of respiration was imaged. CONCLUSION: In vivo studies do not take into account the motion of the highly pliable laryngeal upper airway structures (aryepiglottic, vestibular, and vocal folds). Maximal abduction of these structures with tracheal tubes or bronchoscopes always demonstrates a larger opening of the glottis compared to the outlet of the cricoid ring. Injury to the larynx depends upon ease of tracheal tube or endoscope passage past the cricoid cartilage and not passage through the readily distensible more proximal structures. The infant larynx is funnel shaped with the narrowest portion the circular or near circular cricoid cartilage confirmed by multiple in vitro autopsy specimens carried out over the past century.

Experimental validation of laryngotracheal growth and recurrent laryngeal nerve preservation after partial cricotracheal resection in a growing rabbit model.

PURPOSE: The aim of this study was to confirm laryngotracheal growth and recurrent laryngeal nerve (RLN) preservation after partial cricotracheal resection (PCTR) in a growing rabbit model by performing the procedure in pediatric animals. METHODS: Six female Japanese white rabbits, 12 weeks of age, underwent PCTR. The course of the RLN was evaluated during surgery (n = 3). Endoscopic and histologic examinations were performed at 22 weeks of age (n = 6). Four non-operated rabbits, 22 weeks of age, underwent endoscopic and histologic examinations as controls. RESULTS: The RLN was preserved at the esophageal side and entered the larynx behind the cricothyroid joint after PCTR. Endoscopic examination showed normal vocal cord movements and the large reconstructed subglottis. Histologically, sufficient submucosal vessels and cartilage growth were identified at the reconstructed larynx. The median inside luminal area at the anastomotic site in the PCTR group was 24.8 mm2 (range 21.8-29.0 mm2), and that at the cricoid cartilage and trachea in the control group was 23.4 mm2 (range 20.0-26.6 mm2) and 25.6 mm2 (range 22.9-28.8 mm2), respectively. CONCLUSION: No interference with laryngotracheal growth was seen, and RLN preservation was confirmed after PCTR. Use of PCTR in the pediatric age group seems appropriate.

Age-related changes of the larynx and trachea assessed by three-dimensional computed tomography in children: Application to endotracheal intubation and bronchoscopy.

The purpose of this study was to establish normative data of laryngotracheal dimensions and shape and to evaluate differences associated with age and sex using three-dimensional (3D) imaging. A total of 120 patients (64 boys and 56 girls) were included. Subjects were divided into four groups: Group 1 (0-2 years), Group 2 (3-7 years), Group 3 (8-13 years), and Group 4 (14-20 years). Using 3D image processing software, the laryngeal volume (LV), tracheal volume (TV), anteroposterior diameter at the glottis, cross-sectional area (CSA) at the subglottis, and laryngeal angle (LA) of the thyroid laminae were measured. Parameters of laryngotracheal volume and size were positively correlated with age, whereas the LA was inversely correlated with age. The LV, TV, CSA-3 mm, and CSA-5 mm exhibited a growth spurt in Groups 2 and 3. The LA decreased at a faster rate in Group 1 (P = 0.012). In Groups 1 and 2, there were no differences between genders for each laryngotracheal segmentation or plane. However, gender differences in the TV of Group 3 were statistically significant (P = 0.030). In Group 4, gender differences of all airway parameters were evident. Volume and other dimensions of the laryngotracheal airway increase with age. There was a significant increase in the LV, TV, CSA-3 mm, and CSA-5 mm in Groups 2 and 3. The LA correlated negatively with age in the Group 1. Significant sex dimorphisms are evident in Group 4.

Ephrin-B reverse signaling controls septation events at the embryonic midline through separate tyrosine phosphorylation-independent signaling avenues.

We report that the disruption of bidirectional signaling between ephrin-B2 and EphB receptors impairs morphogenetic cell-cell septation and closure events during development of the embryonic midline. A novel role for reverse signaling is identified in tracheoesophageal foregut septation, as animals lacking the cytoplasmic domain of ephrin-B2 present with laryngotracheoesophageal cleft (LTEC), while both EphB2/EphB3 forward signaling and ephrin-B2 reverse signaling are shown to be required for midline fusion of the palate. In a third midline event, EphB2/EphB3 are shown to mediate ventral abdominal wall closure by acting principally as ligands to stimulate ephrin-B reverse signaling. Analysis of new ephrin-B2(6YFΔV) and ephrin-B2(ΔV) mutants that specifically ablate ephrin-B2 tyrosine phosphorylation- and/or PDZ domain-mediated signaling indicates there are at least two distinct phosphorylation-independent components of reverse signaling. These involve both PDZ domain interactions and a non-canonical SH2/PDZ-independent form of reverse signaling that may utilize associations with claudin family tetraspan molecules, as EphB2 and activated ephrin-B2 molecules are specifically co-localized with claudins in epithelia at the point of septation. Finally, the developmental phenotypes described here mirror common human midline birth defects found with the VACTERL association, suggesting a molecular link to bidirectional signaling through B-subclass Ephs and ephrins.

Age-dependent structural and radiological changes in the larynx.

AIM: To define radiological physiological changes in the larynx by establishing an age-related scale. MATERIALS AND METHODS: The present retrospective study used radiological records of patients that had undergone lateral cervical imaging. Three hundred patients were included. Thyroid cartilage was divided into anatomical regions. The hyoid bone was evaluated as the body and greater horns. Cases were compared by grouping by age and gender. RESULTS: Thyroid tissue and cricoid cartilage only became visible after the second decade. Ossification in the thyroid cartilage began in the posterior inferior horn and progressed to the superior horn and central lamina. It also began in the posterior part of the cricoid cartilage and moved forward with age. In the first decade, the body and greater horn parts of the hyoid bone could be seen more distinctly, and after the third decade the hyoid bone appeared as a single bone. The hyoid bone was the only structure ossified in the laryngeal region below the age of 20 and formed an image on direct imaging. CONCLUSIONS: Age-related changes to the laryngeal tissues are evident on radiographs. Clinicians should bear this in mind when evaluating neck radiographs.

Structural and functional development in airways throughout childhood: Children are not small adults.

Children are not small adults and this fact is particularly true when we consider the respiratory tract. The anatomic peculiarities of the upper airway make infants preferential nasal breathers between 2 and 6 months of life. The pediatric larynx has a more complex shape than previously believed, with the narrowest point located anatomically at the subglottic level and functionally at the cricoid cartilage. Alveolarization of the distal airways starts conventionally at 36-37 weeks of gestation, but occurs mainly after birth, continuing until adolescence. The pediatric chest wall has unique features that are particularly pronounced in infants. Neonates, infants, and toddlers have a higher metabolic rate, and consequently, their oxygen consumption at rest is more than double that of adults. The main anatomical and functional differences between pediatric and adult airways contribute to the understanding of various respiratory symptoms and disease conditions in childhood. Knowing the peculiarities of pediatric airways is helpful in the prevention, management, and treatment of acute and chronic diseases of the respiratory tract. Developmental modifications in the structure of the respiratory tract, in addition to immunological and neurological maturation, should be taken into consideration during childhood.

Development of Excised Larynx.

The larynx is a complex organ which has a role in a variety of functions such as phonation, breathing, and swallowing. To research these functions, it is widely accepted that in vivo studies provide more anatomically and physiologically relevant findings. However, invasive procedures are generally needed to measure variables such a subglottal pressure, vocal fold tension and stiffness, and cricothyroid muscle stretch. Performing studies using excised larynges is a useful technique which makes it possible to not only measure phonation parameters but control them as well. Early studies using excised larynges mainly focused on controlling specific parameters and mathematical modeling simulations. The use of these studies has helped further research in laryngeal anatomy, imaging techniques, as well as aerodynamic, acoustic, and biomechanical properties. Here, we describe the progress of this research over the past 5 years. The number of accepted animal models has increased and ideas from excised larynx studies are starting to be applied to treatment methods for laryngeal disorders. These experiments are only valid for an excised situation and must continue to be combined with animal experimentation and clinical observations.

Pediatric laryngeal dimensions: an age-based analysis.

BACKGROUND: In children, the cricoid is considered the narrowest portion of the "funnel-shaped" airway. Growth and development lead to a transition to the more cylindrical adult airway. A number of airway decisions in pediatric airway practice are based on this transition from the pediatric to the adult airway. Our primary aim in this study was to measure airway dimensions in children of various ages. The measures of the glottis and cricoid regions were used to determine whether a transition from the funnel-shaped pediatric airway to the cylindrical adult airway could be identified based on images obtained from video bronchoscopy. METHODS: One hundred thirty-five children (ASA physical status 1 or 2) aged 6 mo to 13 yr were enrolled for measurement of laryngeal dimensions, including cross-sectional area (G-CSA), anteroposterior and transverse diameters at the level of the glottis and the cricoid (C-CSA), using the video bronchoscopic technique under general anesthesia. RESULTS: Of the 135 children enrolled in the study, seven patients were excluded from the analysis mainly because of poor image quality. Of the 128 children studied (79 boys and 49 girls), mean values (+/-standard deviation) for the demographic data were age 5.9 (+/-3.3) yr, height 113.5 (+/-22.2) cm and weight 23.5 (+/-13) kg. Overall, the mean C-CSA was larger than the G-CSA (48.9 +/- 15.5 mm(2) vs 30 +/- 16.5 mm(2), respectively). This relationship was maintained throughout the study population starting from 6 mo of age (P < 0.001, r = 0.45, power = 1). The mean ratio for C-CSA: G-CSA was 2.1 +/- 1.2. There was a positive correlation between G- and the C-CSA versus age (r = 0.36, P < 0.001; r = 0.27, P = 0.001, respectively), height (r = 0.34, P < 0.001; r = 0.29, P < 0.001, respectively), and weight (r = 0.35, P < 0.001; r = 0.25, P = 0.003, respectively). No significant gender differences in the mean values of the studied variables were observed. CONCLUSION: In this study of infants and children, the glottis rather than cricoid was the narrowest portion of the pediatric airway. Similar to adults, the pediatric airway is more cylindrical than funnel shaped based on these video bronchoscopic images. Further studies are needed to determine whether these static airway measurements in anesthetized and paralyzed children reflect the dynamic characteristics of the glottis and cricoid in children.

A statistical, formant-pattern model for segregating vowel type and vocal-tract length in developmental formant data.

This paper investigates the theoretical basis for estimating vocal-tract length (VTL) from the formant frequencies of vowel sounds. A statistical inference model was developed to characterize the relationship between vowel type and VTL, on the one hand, and formant frequency and vocal cavity size, on the other. The model was applied to two well known developmental studies of formant frequency. The results show that VTL is the major source of variability after vowel type and that the contribution due to other factors like developmental changes in oral-pharyngeal ratio is small relative to the residual measurement noise. The results suggest that speakers adjust the shape of the vocal tract as they grow to maintain a specific pattern of formant frequencies for individual vowels. This formant-pattern hypothesis motivates development of a statistical-inference model for estimating VTL from formant-frequency data. The technique is illustrated using a third developmental study of formant frequencies. The VTLs of the speakers are estimated and used to provide a more accurate description of the complicated relationship between VTL and glottal pulse rate as children mature into adults.

Anatomic development of the oral and pharyngeal portions of the vocal tract: an imaging study.

The growth of the vocal tract (VT) is known to be non-uniform insofar as there are regional differences in anatomic maturation. This study presents quantitative anatomic data on the growth of the oral and pharyngeal portions of the VT from 605 imaging studies for individuals between birth and 19 years. The oral (horizontal) portion of the VT was segmented into lip-thickness, anterior-cavity-length, oropharyngeal-width, and VT-oral, and the pharyngeal (vertical) portion of the VT into posterior-cavity-length, and nasopharyngeal-length. The data were analyzed to determine growth trend, growth rate, and growth type (neural or somatic). Findings indicate differences in the growth trend of segments/variables analyzed, with significant sex differences for all variables except anterior-cavity-length. While the growth trend of some variables displays prepubertal sex differences at specific age ranges, the importance of such localized differences appears to be masked by overall growth rate differences between males and females. Finally, assessment of growth curve type indicates that most VT structures follow a combined/hybrid (somatic and neural) growth curve with structures in the vertical plane having a predominantly somatic growth pattern. These data on the non-uniform growth of the vocal tract reveal anatomic differences that contribute to documented acoustic differences in prepubertal speech production.

Respiratory movement patterns during vocalizations at 7 and 11 months of age.

PURPOSE: The present investigation was designed to study the modulation of abdomen and rib cage movements during vocalization over a period of development associated with rapid decreases in the compliance of the chest wall. METHOD: Rib cage and abdominal kinematics were recorded during spontaneous vocalizations in 7- and 11-month old infants. Principal component analysis was used to represent each infant's abdomen and rib cage traces as the weighted sum of a small number of principal component (PC) waveforms. RESULTS: The fundamental periods of infants' PC waveforms in the 11-month group were significantly shorter than those in the 7-month group. In addition, the variance contributed by PCs describing unidirectional patterns of respiratory movement decreased in the 11-month group, whereas the variances contributed by PCs describing modulated patterns of movement increased. Lastly, the extent to which abdomen and rib cage movements predicted the duration of corresponding vocalizations also increased significantly in the 11-month group compared with the 7-month group. CONCLUSIONS: The findings of the present study were consistent with the hypothesis that decreases in the compliance of the chest wall result in more rapid modulation of chest wall movements and greater control of those movements by the developing neuromuscular system.

Age-related changes of the upper airway assessed by 3-dimensional computed tomography.

The purposes of this study were to establish normative data for airway size and shape and to evaluate differences associated with age and sex using 3-dimensional (3-D) imaging. Patients being evaluated by computed tomography (CT) for pathologic conditions not related to the airway were included. Using 3-D Slicer (Harvard Surgical Planning Laboratory, Brigham and Women's Hospital, Boston, MA), a software program, digital 3-D CT reconstructions were made and parameters of airway size analyzed: volume (VOL), surface area (SA), length (L), mean cross-sectional area (mean CSA), minimum retropalatal (RP), minimum retroglossal (RG), minimum cross-sectional area (min CSA), and lateral (LAT) and anteroposterior (AP) retroglossal airway dimensions. Evaluation of airway shape included LAT/AP and RP/RG ratios, uniformity (U), and sphericity, a measure of compactness (Psi). Children were stratified by stage of dentition: primary, 0 to 5 years; mixed, 6 to 11 years; permanent, 12 to 16 years; and adults, older than 16 years. Differences in airway parameters by age and sex were analyzed. Forty-six CT scans (31 males) were evaluated. Adults had larger (VOL, SA, L, mean CSA, and LAT), more elliptical (increased LAT/AP, P = 0.01), less uniform (U, P = 0.02), and less compact (decreased Psi, P = 0.001) airways than children. Among children, those in the permanent dentition demonstrated greater VOL (P < 0.01), SA (P < 0.01), L (P < 0.01), and mean CSA (P < 0.01) than those in the primary dentition. There were no gender differences in airway parameters. Understanding differences in 3-D airway size and morphology by age may serve as a basis for evaluation of patients with obstructive sleep apnea and may help to predict and to evaluate outcomes of treatment.

The influence of premature birth on laryngeal development for phonation.

INTRODUCTION: Dysphonia is a known consequence of premature birth, and is usually associated with endotracheal intubation in the neonatal period or surgical ligation of persistent patent ductus arteriosus. Recently, cases of dysphonia, in the absence of these causative factors, have been reported. OBJECTIVES: This review seeks to identify literature pertaining to those aspects of laryngeal development that may potentially be disrupted by premature birth. The purpose of the review is to determine whether there is any possible anatomical or physiological explanation for dysphonia to arose solely from premature birth. METHODS: This scoping review was conducted in accordance with the guidelines prescribed by Arskey and O'Malley (2005). Fifteen relevant papers were identified. Results were categorized into age-related categories, to identify changes in the developmental trajectory. Based on the results of the literature search, a further category of unphonated larynges was added. RESULTS: Potential differences in the laryngeal framework (e.g., the development of the cricoid cartilage and the shape of the glottis) and vocal fold histology, depending on gestational age and post-natal phonation were identified. Much literature focused on the macula flavae, however, the layers of the lamina propria were also discussed. DISCUSSION: It is unclear whether the process of differentiation of the layers of the lamina propria, which commences in the second to third months of life in term-born infants, is disrupted by prematurity. Further, development of the macula flavae continues until at least 28 weeks' gestation. Preterm children may not phonate immediately after birth, which may also affect laryngeal development.

A Tutorial of the Effects of Sex Hormones on Laryngeal Senescence and Neuromuscular Response to Exercise.

Purpose The purpose of this tutorial is to summarize how sex hormones affect both laryngeal senescence and neuromuscular response to exercise, highlighting the importance of considering sex differences in developing treatment for the senescent voice. Conclusion Men and women's voices are sexually dimorphic throughout the life span, including during the laryngeal adaptations observed during senescence. Therefore, presbyphonia (age-related dysphonia) likely clinically manifests differently for men and women due to differences in how the male and the female larynx change in response to aging. Because sexual dimorphism is evident in both laryngeal aging and response to exercise, voice therapy programs aimed at treating the typical and disordered aged voice should consider sex differences in their design.

Vocal state change through laryngeal development.

Across vertebrates, progressive changes in vocal behavior during postnatal development are typically attributed solely to developing neural circuits. How the changing body influences vocal development remains unknown. Here we show that state changes in the contact vocalizations of infant marmoset monkeys, which transition from noisy, low frequency cries to tonal, higher pitched vocalizations in adults, are caused partially by laryngeal development. Combining analyses of natural vocalizations, motorized excised larynx experiments, tensile material tests and high-speed imaging, we show that vocal state transition occurs via a sound source switch from vocal folds to apical vocal membranes, producing louder vocalizations with higher efficiency. We show with an empirically based model of descending motor control how neural circuits could interact with changing laryngeal dynamics, leading to adaptive vocal development. Our results emphasize the importance of embodied approaches to vocal development, where exploiting biomechanical consequences of changing material properties can simplify motor control, reducing the computational load on the developing brain.

Development of the supralaryngeal vocal tract in Japanese macaques: implications for the evolution of the descent of the larynx.

The configuration of the supralaryngeal vocal tract depends on the nonuniform growth of the oral and pharyngeal portion. The human pharynx develops to form a unique configuration, with the epiglottis losing contact with the velum. This configuration develops from the great descent of the larynx relative to the palate, which is accomplished through both the descent of the laryngeal skeleton relative to the hyoid and the descent of the hyoid relative to the palate. Chimpanzees show both processes of laryngeal descent, as in humans, but the evolutionary path before the divergence of the human and chimpanzee lineages is unclear. The development of laryngeal descent in six living Japanese macaque monkeys, Macaca fuscata, was examined monthly during the first three years of life using magnetic resonance imaging, to delineate the present or absence of these two processes and their contributions to the development of the pharyngeal topology. The macaque shows descent of the hyoid relative to the palate, but lacks the descent of the laryngeal skeleton relative to the hyoid and that of the EG from the VL. We argue that the former descent is simply a morphological consequence of mandibular growth and that the latter pair of descents arose in a common ancestor of extant hominoids. Thus, the evolutionary path of the great descent of the larynx is likely to be explained by a model comprising multiple and mosaic evolutionary pathways, wherein these developmental phenomena may have contributed secondarily to the faculty of speech in the human lineage.

Patterns of acquisition of native voice onset time in English-learning children.

Learning to speak involves both mastering the requisite articulatory gestures of one's native language and learning to coordinate those gestures according to the rules of the language. Voice onset time (VOT) acquisition illustrates this point: The child must learn to produce the necessary upper vocal tract and laryngeal gestures and to coordinate them with very precise timing. This longitudinal study examined the acquisition of English VOT by audiotaping seven children at 2 month intervals from first words (around 15 months) to the appearance of three-word sentences (around 30 months) in spontaneous speech. Words with initial stops were excerpted, and (1) the numbers of words produced with intended voiced and voiceless initial stops were counted; (2) VOT was measured; and (3) within-child standard deviations of VOT were measured. Results showed that children (1) initially avoided saying words with voiceless initial stops, (2) initially did not delay the onset of the laryngeal adduction relative to the release of closure as long as adults do for voiceless stops, and (3) were more variable in VOT for voiceless than for voiced stops. Overall these results support a model of acquisition that focuses on the mastery of gestural coordination as opposed to the acquisition of segmental contrasts.