Morphological variation in the adult hard palate and posterior pharyngeal wall

Morphological and acoustic modeling of the vocal tract

In speech production, the anatomical morphology forms the substrate on which the speakers build their articulatory strategy to reach specific articulatory-acoustic goals. The aim of this study is to characterize morphological inter-speaker variability by building a shape model of the full vocal tract including hard and soft structures. Static magnetic resonance imaging data from 41 speakers articulating altogether 1947 phonemes were considered, and the midsagittal articulator contours were manually outlined. A phoneme-independent average-articulation representative of morphology was calculated as the speaker mean articulation. A principal component analysis-driven shape model was derived from average-articulations, leading to five morphological components, which explained 87% of the variance. Almost three-quarters of the variance was related to independent variations of the horizontal oral and vertical pharyngeal lengths, the latter capturing male-female differences. The three additional components captured shape variations related to head tilt and palate shape. Plane wave propagation acoustic simulations were run to characterize morphological components. A lengthening of 1 cm of the vocal tract in the vertical or horizontal directions led to a decrease in formant values of 7%-8%. Further analyses are required to analyze three-dimensional variability and to understand the morphological-acoustic relationships per phoneme. Average-articulations and model code are publicly available (https://github.com/tonioser/VTMorphologicalModel).

Palatal surface development from 6 years of age to early adulthood: data modelling using 3D geometric morphometrics

OBJECTIVES

The study followed the modelling of postnatal growth of a healthy palate of the Central European (Czech) population sample based on transverse data on sex and age from 6 to 19 years.

MATERIALS AND METHODS

Digitised 3D models of 212 healthy palatal surfaces were evaluated using 3D geometric morphometrics and superimpositions. The individuals were grouped based on age (preschool, younger and older school age, younger and older adolescents, young adults) and sex (♂ n = 101, ♀ n = 111).

RESULTS

Female palatal development was non-linear and was interrupted between the 10-12 years and then proceeded intensively until the age of 15 when it ceased. In contrast, male-modelled growth was consistent throughout the follow-up and continued linearly until at least 19 years of age. The palate did not widen further with increasing age, and primarily palatal vaulting and heightening were found. The characteristics and distribution of areas with extensive modelled growth changes were comparable in females and males, as confirmed by the location of principal components (PC1 and PC2) within modal space and growth trajectories. The extent of sexual dimorphism increased from 15 years of age due to pubertal spurt combined with earlier completion of palatal development in females.

CONCLUSIONS

The study showed modelled healthy palatal development from 6 years of age to early adulthood, which might be utilised as reference standards for the Central European population sample.

CLINICAL RELEVANCE

The comparison of normal reference subjects with patients with cranio-maxillo-facial dysmorphologies represents the first step in diagnosing and establishing effective therapy.

Influence of the palatal plane cant and skeletal patterns in the hard palate thickness?

INTRODUCTION

The aim of the present study was to evaluate the thickness of the hard palate at the different angles formed by the palatal plane and the Frankfort horizontal line using computed tomography in patients with different facial patterns for planning the installation of MARPE.

MATERIALS AND METHODS

The measurements were analysed in the hard palate of 106 patients. Four regions were selected passing through the mesial face, tangent at the level of the cemento-enamel junction of the premolars and molars. The bone thickness was measured from the floor of the nasal cavity to the cortical bone of the hard palate, 02 measurements with a distance of 05 mm between them (2.5 mm on each side starting from the midsagittal line) and 2 more with a distance of 7 mm between measurements (3.5 mm on each side starting from the midsagittal line). The palatal plane cant was determined based on the palatal plane and the Frankfort horizontal plane. The sagittal skeletal pattern was determined based on the ANB angle and the vertical skeletal pattern based on the SN.Go.Gn angle.

RESULTS

Palatal bone thickness was greater in males than in females. Regarding the sagittal skeletal pattern, patients with Class II were found to have a thinner hard palate than Class I and Class III patients. No difference in the vertical skeletal pattern was observed between groups. Regarding the palatal plane cant, bone thickness was greater in patients with clockwise rotation.

CONCLUSIONS

Careful planning should be considered in the case of female patients; patients with greater angles of the palatal plane cant and Class II patients have a smaller bone thickness.

Audit and Comparison Between Radiographic Markers of Gaze Direction Using EOS Imaging - An Essential Step to Streamline Existing Methods

STUDY DESIGN

Retrospective cohort study on prospectively implemented EOS protocol.

OBJECTIVE

This study aims to audit and compare existing radiological definitions of gaze direction-chin brow vertical angle (CBVA), McGregor slope (McGS), slope of line of sight (SLS), orbital-internal occipital protuberance (OIOP) slope angle, and Tangent to the hard palate (THP) in a neutral, healthy, and asymptomatic cohort.

SUMMARY OF BACKGROUND DATA

The ability to accurately define direction of gaze is the first step when striving for horizontal gaze restoration in any affected individual with rigid sagittal deformity. Yet, the radiological definition of gaze direction remains poorly standardized.

METHODS

Hundred healthy subjects who could achieve horizontal gaze underwent whole-body standing EOS radiographs taken under a strictly standardized protocol. Radiographic measurements of global spinal sagittal parameters and surrogate measures of horizontal gaze were analyzed and compared.

RESULTS

The mean age was 45 ± 15.9 years, with a balanced male-to-female-ratio. Their C7 SVA was -7.7 mm ± 24.8 mm, PI was 51.0o ± 11.4o, PI-LL was -0.9o ± 13.0o and T1-slope was 21.2o ± 9.2o. Measured horizontal gaze parameters were as follows: CBVA (1.07o ± 5.48o), McGS (-3.23o ± 5.63o), SLS (0.45o ± 5.34o), OIOP (5.03o ± 4.66o), THP (-0.17o ± 6.27o). CBVA correlated strongly with McGS (r = 0.679, P < 0.001), SLS (r = 0.592, P < 0.001), OIOP (r = 0.697, P < 0.001), and THP (r = -0.504, P < 0.001). OIOP had the lowest variance amongst all parameters and showed less variability compared to CBVA (SD 4.66 Var 21.69 vs. SD 5.48 Var 30.08, P = .012). Multivariate analysis showed that C2-7 angle was the only parameter found to be associated with OIOP values (P = 0.006).

CONCLUSION

OIOP is the least variable, and most robust radiological method in determining gaze direction. It uses easily recognizable anatomical landmarks and an angular criterion, which makes it advantageous both with x-rays or slot scanners.Level of Evidence: 3.

Exploring directional and fluctuating asymmetry in the human palate during growth

Objectives

Palate morphology is constantly changing throughout an individual's lifespan, yet its asymmetry during growth is still little understood. In this research, we focus on the study of palate morphology by using 3D geometric morphometric approaches to observe changes at different stages of life, and to quantify the impact of directional and fluctuating asymmetry on different areas at different growth stages.

Materials and Methods

The sample consists of 183 individuals (1–72 years) from two identified human skeletal collections of 19th and early 20th Century Italian contexts. A 3D‐template of 41 (semi)landmarks was applied on digital palate models to observe morphological variation during growth.

Results

Asymmetrical components of the morphological structure appears multidirectional on the entire palate surface in individuals <2 years old and become oriented (opposite bilateral direction) between 2 and 6 years of age. Specifically, directional asymmetry differentially impacts palate morphology at different stages of growth. Both the anterior and posterior palate are affected by mild alterations in the first year of life, while between 2 and 6 years asymmetry is segregated in the anterior area, and moderate asymmetry affects the entire palatal surface up to 12 years of age. Our results show that stability of the masticatory system seems to be reached around 13–35 years first by females and then males. From 36 years on both sexes show similar asymmetry on the anterior area. Regarding fluctuating asymmetry, inter‐individual variability is mostly visible up to 12 years of age, after which only directional trends can be clearly observed at a group level.

Discussion

Morphological structure appears instable during the first year of life and acquires an opposite asymmetric bilateral direction between 2 and 6 years of age. This condition has been also documented in adults; when paired with vertical alteration, anterior/posterior asymmetry seems to characterize palate morphology, which is probably due to mechanical factors during the lifespan. Fluctuating asymmetry is predominant in the first period of life due to a plausible relationship with the strength of morphological instability of the masticatory system. Directional asymmetry, on the other hand, shows that the patterning of group‐level morphological change might be explained as a functional response to differential inputs (physiological forces, nutritive and non‐nutritive habits, para‐masticatory activity as well as the development of speech) in different growth stages. This research has implications with respect to medical and evolutionary fields. In medicine, palate morphology should be considered when planning orthodontic and surgical procedures as it could affect the outcome. As far as an evolutionary perspective is concerned the dominance of directional asymmetries in the masticatory system could provide information on dietary and cultural habits as well as pathological conditions in our ancestors.

The vocal tract as a time machine: inferences about past speech and language from the anatomy of the speech organs

While speech and language do not fossilize, they still leave traces that can be extracted and interpreted. Here, we suggest that the shape of the hard structures of the vocal tract may also allow inferences about the speech of long-gone humans. These build on recent experimental and modelling studies, showing that there is extensive variation between individuals in the precise shape of the vocal tract, and that this variation affects speech and language. In particular, we show that detailed anatomical information concerning two components of the vocal tract (the lower jaw and the hard palate) can be extracted and digitized from the osteological remains of three historical populations from The Netherlands, and can be used to conduct three-dimensional biomechanical simulations of vowel production. We could recover the signatures of inter-individual variation between these vowels, in acoustics and articulation. While 'proof-of-concept', this study suggests that older and less well-preserved remains could be used to draw inferences about historic and prehistoric languages. Moreover, it forces us to clarify the meaning and use of the uniformitarian principle in linguistics, and to consider the wider context of language use, including the anatomy, physiology and cognition of the speakers. This article is part of the theme issue 'Reconstructing prehistoric languages'.

Palate shape influence depends on the segment: Articulatory and acoustic variability in American English /ɹ/ and /s/

This ultrasound and acoustics study of American English /ɹ/ and /s/ investigates whether variability in production as measured in the midsagittal plane is related to individual differences in the shape of the hard palate in the coronal plane. Both token-to-token variability and variability between different phonetic contexts were investigated. While no direct relationship was found between palate flatness and articulatory variability, a secondary analysis revealed that speakers' articulatory variability for one segment was related to their variability in the other. Speakers with flatter palates tended towards lower articulatory variability scores, but speakers with more domed palates showed both high and low variability scores.

Classification and Morphological Analysis of the Hard Palate in Cone-Beam Computed Tomography Scans: A Retrospective Study

PURPOSE

As the hard palate is a central structure of the skull and is involved in orthodontic and surgical procedures, it would be of interest to study the morphological aspects of this bone and its possible variations as per different patterns of skeletal development. Thus, this study aimed to develop a classification for the different morphological characteristics of the hard palate and to evaluate the relationship between these characteristics and the different skeletal patterns, using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

This retrospective and cross-sectional study used CBCT scans of patients seen from January 2014 to December 2016. Carestream Dental 3D Imaging software was applied to classify each patient according to vertical and sagittal skeletal patterns, and to evaluate the 3 morphological characteristics of the hard palate: depth (flat, regular, or deep), inclination (superior, parallel, or inferior), and presence of a bony projection (S-shaped). χ² and Fisher's exact tests evaluated the relationship between the hard palate characteristics and the different skeletal patterns.

RESULTS

A total of 298 CBCT scans (144 males and 154 females) were evaluated. The depth of the hard palate was significantly related to both skeletal patterns in males (P < .05), with Class II and dolichocephalics presenting a greater amount of deep palates, while classes I and III and brachycephalics had a greater amount of regular palates. The inclination of the hard palate was significantly associated with the facial type in females (P < .05), with brachycephalics and mesocephalics presenting a greater amount of parallel palates, whereas dolichocephalics had a greater number of inferiorly inclined palates. Regarding the presence of the S-shape in the hard palate, there was a greater number of this projection in Class II males and brachycephalic females.

CONCLUSIONS

A morphological classification for the hard palate was developed. The morphology of the hard palate varied among the different skeletal patterns.

Radiological approach to basilar invagination type B: Reliability and accuracy

OBJECTIVES

This study aims to determine the reliability of the radiological tests used in the diagnosis of basilar invagination (BI).

METHODS

Patients diagnosed with type B basilar invagination, who had both magnetic resonance (MR) and computed tomography (CT) imaging between January 2014 and November 2019 were included in this retrospective reliability study. In this study, distance from odontoid apex to Chamberlain's line (OA-CL) was accepted as a reference method for the diagnosis. Forty-two BI cases and 79 controls were included. Three radiologists with different levels of experience individually evaluated OA-CL, Boogard's angle (BoA), clivo-axial angle (CXA), clivo-dens angle (CDA), and clivo-palate angle (CPA) on midsagittal CT and MR images. Statistical analysis was made with the intraclass correlation coefficient (ICC), t-test, and receiver operating characteristic (ROC) curve.

RESULTS

The ICC for CT and MR were; 0.977-0.973 (OA-CL), 0.912-0.882 (BoA), 0.845-0.846 (CXA), 0.862-0.864 (CDA), and 0.762-0.747 (CPA) respectively (P < 0.001). The areas under the ROC curve were 0.977 (BoA), 0.832 (CXA), 0.852 (CDA), and 0.719 (CPA) (P < 0.001). The cut-off measures were ≥137.84° (BoA), ≤149.25° (CXA), ≤129.58° (CDA), and ≤61.83° (CPA). The diagnostic accuracies were 0.954 (BoA), 0.664 (CXA), 0.704 (CDA), 0.438 (CPA) (P < 0.001).

CONCLUSIONS

OA-CL and BoA express excellent inter-rater agreement than CXA, CDA, and CPA, which are limited due to morphological variations and head spatial position. BoA is the second most reliable diagnostic test. CXA, CDA, should only be used for complementary information. CPA was found inadequate for the diagnosis of BI..

Native Language Influence on Brass Instrument Performance: An Application of Generalized Additive Mixed Models (GAMMs) to Midsagittal Ultrasound Images of the Tongue

This paper presents the findings of an ultrasound study of 10 New Zealand English and 10 Tongan-speaking trombone players, to determine whether there is an influence of native language speech production on trombone performance. Trombone players' midsagittal tongue shapes were recorded while reading wordlists and during sustained note productions, and tongue surface contours traced. After normalizing to account for differences in vocal tract shape and ultrasound transducer orientation, we used generalized additive mixed models (GAMMs) to estimate average tongue surface shapes used by the players from the two language groups when producing notes at different pitches and intensities, and during the production of the monophthongs in their native languages. The average midsagittal tongue contours predicted by our models show a statistically robust difference at the back of the tongue distinguishing the two groups, where the New Zealand English players display an overall more retracted tongue position; however, tongue shape during playing does not directly map onto vowel tongue shapes as prescribed by the pedagogical literature. While the New Zealand English-speaking participants employed a playing tongue shape approximating schwa and the vowel used in the word 'lot,' the Tongan participants used a tongue shape loosely patterning with the back vowels /o/ and /u/. We argue that these findings represent evidence for native language influence on brass instrument performance; however, this influence seems to be secondary to more basic constraints of brass playing related to airflow requirements and acoustical considerations, with the vocal tract configurations observed across both groups satisfying these conditions in different ways. Our findings furthermore provide evidence for the functional independence of various sections of the tongue and indicate that speech production, itself an acquired motor skill, can influence another skilled behavior via motor memory of vocal tract gestures forming the basis of local optimization processes to arrive at a suitable tongue shape for sustained note production.

Palatal morphology in unilateral cleft lip and palate patients: Association with infant cleft dimensions and timing of hard palate repair

OBJECTIVES

To assess the impact of cleft severity and timing of hard palate repair on palatal dimensions in unilateral cleft lip and palate (UCLP) children.

SETTING AND SAMPLE POPULATION

Single-centre analysis within a multicenter RCT of primary surgery; 122 UCLP randomized to early hard palate closure (EHPC) at 12 months or delayed hard palate closure (DHPC) at 36 months; 28 frequency-matched controls.

METHODS

Linear measurements of palatal height, width and length were performed on 116 digital models of UCLP subjects (8.21 years, SD = 0.53) and 28 models of non-cleft individuals (8.44 years SD = 0.72). Cleft dimensions at infancy (mean 1.8 months) were considered. In a pilot study, shell-to-shell distances between the 3D cleft palate objects and a reference mesh were calculated and differences between the groups assessed. Morphological differences were visualized using colour mapping.

RESULTS

Compared to controls, UCLP subjects presented a higher palate at the level of the anterior scar (P = 0.002), but generally a lower palate in the middle region (P < 0.001). Comparing UCLP subgroups, the DHPC subjects showed a flatter palate posteriorly (P = 0.048) and the EHPC group exhibited more transversal constriction (P = 0.003 at M1 level). 3D analysis revealed a shallower palate in the DHPC group both in the middle (P = 0.002) and the posterior part (P = 0.008). Anterior cleft severity correlated negatively with palatal height (P = 0.01).

CONCLUSIONS

Unilateral cleft lip and palate palates differ from controls in width and height. DHPC may represent an advantage for the transversal dimension, but a disadvantage for palatal height. Infant cleft dimensions partially explain differences in palatal height.

Task-dependence of articulator synergies

In speech production, the motor system organizes articulators such as the jaw, tongue, and lips into synergies whose function is to produce speech sounds by forming constrictions at the phonetic places of articulation. The present study tests whether synergies for different constriction tasks differ in terms of inter-articulator coordination. The test is conducted on utterances [ɑpɑ], [ɑtɑ], [ɑiɑ], and [ɑkɑ] with a real-time magnetic resonance imaging biomarker that is computed using a statistical model of the forward kinematics of the vocal tract. The present study is the first to estimate the forward kinematics of the vocal tract from speech production data. Using the imaging biomarker, the study finds that the jaw contributes least to the velar stop for [k], more to pharyngeal approximation for [ɑ], still more to palatal approximation for [i], and most to the coronal stop for [t]. Additionally, the jaw contributes more to the coronal stop for [t] than to the bilabial stop for [p]. Finally, the study investigates how this pattern of results varies by participant. The study identifies differences in inter-articulator coordination by constriction task, which support the claim that inter-articulator coordination differs depending on the active articulator synergy.

Morphometric covariation between palatal shape and skeletal pattern in children and adolescents: a cross-sectional study

Objective

To assess shape covariation of the palate and craniofacial complex (CFC) in children and adolescents.

Methods

Pre-treatment lateral cephalometric radiographs and corresponding maxillary casts of 100 children (8-10 years) and 100 adolescents (15-20 years) were digitized. Exclusion criteria were previous orthodontic treatment, craniofacial syndromes, mouth breathing, finger sucking, crossbite, tooth agenesis, and tooth impaction. Palatal shape was described with 239 surface and curve semilandmarks and craniofacial shape with 10 fixed landmarks and 117 curve semilandmarks. Procrustes superimposition and principal component analysis were applied for evaluation of shape variability. Shape covariation between palate and CFC was assessed with partial least squares analysis.

Results

The first five principal components explained 77 per cent (palate) and 60 per cent (CFC) of total shape variability. The palate varied mainly in height (adolescent group) and width-length (both groups), whereas the CFC varied mainly in the vertical dimension. Significant covariation was found between the craniofacial and palatal components (RV coefficient: 0.27, children; RV: 0.23, adolescents). Variation of the CFC in the vertical and anteroposterior direction was mainly related to variation in the height-width and the width-length ratio of the palate, respectively.

Limitations

The use of lateral cephalometric radiographs eliminated the transverse dimension from the craniofacial shape analysis. The study was cross-sectional, so the observed intergroup differences should be interpreted with caution.

Conclusions

Covariation strength and pattern were similar in children and adolescents. The closer a subject was to the high-angle end of the variability spectrum, the higher and narrower was the palate, and conversely.

Speed-accuracy tradeoffs in human speech production

Speech motor actions are performed quickly, while simultaneously maintaining a high degree of accuracy. Are speed and accuracy in conflict during speech production? Speed-accuracy tradeoffs have been shown in many domains of human motor action, but have not been directly examined in the domain of speech production. The present work seeks evidence for Fitts' law, a rigorous formulation of this fundamental tradeoff, in speech articulation kinematics by analyzing USC-TIMIT, a real-time magnetic resonance imaging data set of speech production. A theoretical framework for considering Fitts' law with respect to models of speech motor control is elucidated. Methodological challenges in seeking relationships consistent with Fitts' law are addressed, including the operational definitions and measurement of key variables in real-time MRI data. Results suggest the presence of speed-accuracy tradeoffs for certain types of speech production actions, with wide variability across syllable position, and substantial variability also across subjects. Coda consonant targets immediately following the syllabic nucleus show the strongest evidence of this tradeoff, with correlations as high as 0.72 between speed and accuracy. A discussion is provided concerning the potentially limited applicability of Fitts' law in the context of speech production, as well as the theoretical context for interpreting the results.

Modelling human hard palate shape with Bézier curves

People vary at most levels, from the molecular to the cognitive, and the shape of the hard palate (the bony roof of the mouth) is no exception. The patterns of variation in the hard palate are important for the forensic sciences and (palaeo)anthropology, and might also play a role in speech production, both in pathological cases and normal variation. Here we describe a method based on Bézier curves, whose main aim is to generate possible shapes of the hard palate in humans for use in computer simulations of speech production and language evolution. Moreover, our method can also capture existing patterns of variation using few and easy-to-interpret parameters, and fits actual data obtained from MRI traces very well with as little as two or three free parameters. When compared to the widely-used Principal Component Analysis (PCA), our method fits actual data slightly worse for the same number of degrees of freedom. However, it is much better at generating new shapes without requiring a calibration sample, its parameters have clearer interpretations, and their ranges are grounded in geometrical considerations.

Test-retest repeatability of human speech biomarkers from static and real-time dynamic magnetic resonance imaging

Static anatomical and real-time dynamic magnetic resonance imaging (RT-MRI) of the upper airway is a valuable method for studying speech production in research and clinical settings. The test-retest repeatability of quantitative imaging biomarkers is an important parameter, since it limits the effect sizes and intragroup differences that can be studied. Therefore, this study aims to present a framework for determining the test-retest repeatability of quantitative speech biomarkers from static MRI and RT-MRI, and apply the framework to healthy volunteers. Subjects (n = 8, 4 females, 4 males) are imaged in two scans on the same day, including static images and dynamic RT-MRI of speech tasks. The inter-study agreement is quantified using intraclass correlation coefficient (ICC) and mean within-subject standard deviation (σ_e). Inter-study agreement is strong to very strong for static measures (ICC: min/median/max 0.71/0.89/0.98, σ_e: 0.90/2.20/6.72 mm), poor to strong for dynamic RT-MRI measures of articulator motion range (ICC: 0.26/0.75/0.90, σ_e: 1.6/2.5/3.6 mm), and poor to very strong for velocities (ICC: 0.21/0.56/0.93, σ_e: 2.2/4.4/16.7 cm/s). In conclusion, this study characterizes repeatability of static and dynamic MRI-derived speech biomarkers using state-of-the-art imaging. The introduced framework can be used to guide future development of speech biomarkers. Test-retest MRI data are provided free for research use.

Characterizing Articulation in Apraxic Speech Using Real-Time Magnetic Resonance Imaging

Purpose

Real-time magnetic resonance imaging (MRI) and accompanying analytical methods are shown to capture and quantify salient aspects of apraxic speech, substantiating and expanding upon evidence provided by clinical observation and acoustic and kinematic data. Analysis of apraxic speech errors within a dynamic systems framework is provided and the nature of pathomechanisms of apraxic speech discussed.

Method

One adult male speaker with apraxia of speech was imaged using real-time MRI while producing spontaneous speech, repeated naming tasks, and self-paced repetition of word pairs designed to elicit speech errors. Articulatory data were analyzed, and speech errors were detected using time series reflecting articulatory activity in regions of interest.

Results

Real-time MRI captured two types of apraxic gestural intrusion errors in a word pair repetition task. Gestural intrusion errors in nonrepetitive speech, multiple silent initiation gestures at the onset of speech, and covert (unphonated) articulation of entire monosyllabic words were also captured.

Conclusion

Real-time MRI and accompanying analytical methods capture and quantify many features of apraxic speech that have been previously observed using other modalities while offering high spatial resolution. This patient's apraxia of speech affected the ability to select only the appropriate vocal tract gestures for a target utterance, suppressing others, and to coordinate them in time.

Advances in real-time magnetic resonance imaging of the vocal tract for speech science and technology research

Real-time magnetic resonance imaging (rtMRI) of the moving vocal tract during running speech production is an important emerging tool for speech production research providing dynamic information of a speaker's upper airway from the entire mid-sagittal plane or any other scan plane of interest. There have been several advances in the development of speech rtMRI and corresponding analysis tools, and their application to domains such as phonetics and phonological theory, articulatory modeling, and speaker characterization. An important recent development has been the open release of a database that includes speech rtMRI data from five male and five female speakers of American English each producing 460 phonetically balanced sentences. The purpose of the present paper is to give an overview and outlook of the advances in rtMRI as a tool for speech research and technology development.

The Articulatory Phonetics of /r/ for Residual Speech Errors

Effective treatment for children with residual speech errors (RSEs) requires in-depth knowledge of articulatory phonetics, but this level of detail may not be provided as part of typical clinical coursework. At a time when new imaging technologies such as ultrasound continue to inform our clinical understanding of speech disorders, incorporating contemporary work in the basic articulatory sciences into clinical training becomes especially important. This is particularly the case for the speech sound most likely to persist among children with RSEs-the North American English rhotic sound, /r/. The goal of this article is to review important information about articulatory phonetics as it affects children with RSE who present with /r/ production difficulties. The data presented are largely drawn from ultrasound and magnetic resonance imaging studies. This information will be placed in a clinical context by comparing productions of typical adult speakers to successful versus misarticulated productions of two children with persistent /r/ difficulties.

Speaker verification based on the fusion of speech acoustics and inverted articulatory signals

We propose a practical, feature-level and score-level fusion approach by combining acoustic and estimated articulatory information for both text independent and text dependent speaker verification. From a practical point of view, we study how to improve speaker verification performance by combining dynamic articulatory information with the conventional acoustic features. On text independent speaker verification, we find that concatenating articulatory features obtained from measured speech production data with conventional Mel-frequency cepstral coefficients (MFCCs) improves the performance dramatically. However, since directly measuring articulatory data is not feasible in many real world applications, we also experiment with estimated articulatory features obtained through acoustic-to-articulatory inversion. We explore both feature level and score level fusion methods and find that the overall system performance is significantly enhanced even with estimated articulatory features. Such a performance boost could be due to the inter-speaker variation information embedded in the estimated articulatory features. Since the dynamics of articulation contain important information, we included inverted articulatory trajectories in text dependent speaker verification. We demonstrate that the articulatory constraints introduced by inverted articulatory features help to reject wrong password trials and improve the performance after score level fusion. We evaluate the proposed methods on the X-ray Microbeam database and the RSR 2015 database, respectively, for the aforementioned two tasks. Experimental results show that we achieve more than 15% relative equal error rate reduction for both speaker verification tasks.

Gender categorization is abnormal in cochlear implant users

In normal hearing (NH), the perception of the gender of a speaker is strongly affected by two anatomically related vocal characteristics: the fundamental frequency (F0), related to vocal pitch, and the vocal tract length (VTL), related to the height of the speaker. Previous studies on gender categorization in cochlear implant (CI) users found that performance was variable, with few CI users performing at the level of NH listeners. Data collected with recorded speech produced by multiple talkers suggests that CI users might rely more on F0 and less on VTL than NH listeners. However, because VTL cannot be accurately estimated from recordings, it is difficult to know how VTL contributes to gender categorization. In the present study, speech was synthesized to systematically vary F0, VTL, or both. Gender categorization was measured in CI users, as well as in NH participants listening to unprocessed (only synthesized) and vocoded (and synthesized) speech. Perceptual weights for F0 and VTL were derived from the performance data. With unprocessed speech, NH listeners used both cues (normalized perceptual weight: F0 = 3.76, VTL = 5.56). With vocoded speech, NH listeners still made use of both cues but less efficiently (normalized perceptual weight: F0 = 1.68, VTL = 0.63). CI users relied almost exclusively on F0 while VTL perception was profoundly impaired (normalized perceptual weight: F0 = 6.88, VTL = 0.59). As a result, CI users' gender categorization was abnormal compared to NH listeners. Future CI signal processing should aim to improve the transmission of both F0 cues and VTL cues, as a normal gender categorization may benefit speech understanding in competing talker situations.

Interspeaker variability in hard palate morphology and vowel production

PURPOSE

Differences in vocal tract morphology have the potential to explain interspeaker variability in speech production. The potential acoustic impact of hard palate shape was examined in simulation, in addition to the interplay among morphology, articulation, and acoustics in real vowel production data.

METHOD

High-front vowel production from 5 speakers of American English was examined using midsagittal real-time magnetic resonance imaging data with synchronized audio. Relationships among hard palate morphology, tongue shaping, and formant frequencies were analyzed. Simulations were performed to determine the acoustical properties of vocal tracts whose area functions are altered according to prominent hard palate variations.

RESULTS

Simulations revealed that altering the height and position of the palatal dome alters formant frequencies. Examinations of real speech data showed that palatal morphology is not significantly correlated with any formant frequency but is correlated with major aspects of lingual articulation.

CONCLUSION

Certain differences in hard palate morphology can substantially affect vowel acoustics, but those effects are not noticeable in real speech. Speakers adapt their lingual articulation to accommodate palate shape differences with the potential to substantially affect formant frequencies, while ignoring palate shape differences with relatively little acoustic impact, lending support for acoustic goals of vowel production.