Speech Adaptation Research Articles

Recalibration of auditory perception of speech due to orofacial somatosensory inputs during speech motor adaptation.

Speech motor control and learning rely on both somatosensory and auditory inputs. Somatosensory inputs associated with speech production can also affect the process of auditory perception of speech, and the somatosensory-auditory interaction may play a fundamental role in auditory perception of speech. In this report, we show that the somatosensory system contributes to perceptual recalibration, separate from its role in motor function. Subjects participated in speech motor adaptation to altered auditory feedback. Auditory perception of speech was assessed in phonemic identification tests before and after speech adaptation. To investigate a role of the somatosensory system in motor adaptation and subsequent perceptual change, we applied orofacial skin stretch in either a backward or forward direction during the auditory feedback alteration as a somatosensory modulation. We found that the somatosensory modulation did not affect the amount of adaptation at the end of training, although it changed the rate of adaptation. However, the perception following speech adaptation was altered depending on the direction of the somatosensory modulation. Somatosensory inflow rather than motor outflow thus drives changes to auditory perception of speech following speech adaptation, suggesting that somatosensory inputs play an important role in tuning of perceptual system.NEW & NOTEWORTHY This article reports that the somatosensory system works not equally with the motor system, but predominantly in the calibration of auditory perception of speech by speech production.

PHONETIC REHABILITATION FOR REMOVABLE DENTAL PROSTHETICS

Removable prosthesis is considered as a device with therapeutic, rehab and prophylactic functions, which allows to improve the quality of life of the dentist. Its use is always aimed at solving three problems: restoration of chewing; restoration of pronunciation of sounds; restoration of aesthetic norms of a person.
 Fixation of the complete removable denture depends on the anatomical retention, which is determined by the area and form of the prosthetic bed; from adhesion (capillary forces, viscosity of saliva) and from the functional suction of the prosthesis. For the stabilization of prostheses, the contour of the alveolar appendix and the production of artificial teeth are of special importance.
 Therefore, a complete removable denture is a complex design, which always has a single plan of construction (basis and artificial teeth), but in each case is made taking into account the individual characteristics of the patient's body.
 Adaptation to a complete removable denture is a multi-layered process. Its inalienable component is neuro-reflex mechanisms. From these positions, the habit of prosthetics is explained by the development of cortical inhibition, which leads to the disappearance of the feeling of a foreign subject in the oral cavity. These changes occur on the basis of the general law, according to which repeatedly the stimulus becomes a brake agent. Based on masticatography, it has been established that addiction to prosthetics is associated with the appearance, perfection and consolidation of new conditioned motor reflexes. An important component of the adaptation process in patients with prosthetics is psychological adaptation. It is believed that it represents the sum of complex conditioned-reflex responses of the patient, which belong to the sphere of human emotions and determine the degree of satisfaction with dentures. The significance of psychological factors in the development of adaptation to prosthetics stimulates the creation of new and improved existing methods for assessing the psycho-emotional state of orthopedic dental patients. According to the results of these methods, high personal anxiety is the main factor that causes the development of psycho-emotional stress during orthopedic treatment.
 There is also a speech adaptation, which is the result of the interaction of the active organs of the articulation apparatus with dentures. The appearance of improper pronunciation of sounds is considered as a result of motor and sensory disorders of the central or peripheral nature: changes in the structure of the articulation apparatus and violations of muscle inertia involved in articulation; reduction of peripheral hearing and violations of the auditory perception of the central character. Wrong pronunciation is most often observed in groups of whistling, silent sounds, [p], [l], which are characterized by complexity of sounding and, accordingly, the complexity of articulation work. A certain range of works is devoted to methods of studying pronunciation of sounds from different points of view: physical (acoustic), anatomical-physiological and linguistic.
 Detection of defects of articulation was done by listening. In a number of studies the study of violations of articulation of sounds was carried out using anatomical-physiological and acoustic characteristics with the help of apparatus. Modern methods of speech research are based on listening, audiometry and spectral analysis of sound.
 Consequently, the features of rehabilitation of toothless patients with the help of a complete removable denture are widely covered in the literature. The concept of pathogenesis of violations with full or partial adentia and about mechanisms of their overcoming with the help of dentures is deepened. However, until now, the literature remains almost uninvolved into the consideration of phonetic aspects as in the analysis of anatomical and physiological features of the toothless mouth during preparation for prosthetics, and at different stages of the use of dentures.

Clear speech adaptations in spontaneous speech produced by young and older adults.

The study investigated the speech adaptations by older adults (OA) with and without age-related hearing loss made to communicate effectively in challenging communicative conditions. Acoustic analyses were carried out on spontaneous speech produced during a problem-solving task (diapix) carried out by talker pairs in different listening conditions. There were 83 talkers of Southern British English. Fifty-seven talkers were OAs aged 65-84, 30 older adults with normal hearing (OANH), and 27 older adults with hearing loss (OAHL) [mean pure tone average (PTA) 0.250-4 kHz: 27.7 dB HL]. Twenty-six talkers were younger adults (YA) aged 18-26 with normal hearing. Participants were recorded while completing the diapix task with a conversational partner (YA of the same sex) when (a) both talkers heard normally (NORM), (b) the partner had a simulated hearing loss, and (c) both talkers heard babble noise. Irrespective of hearing status, there were age-related differences in some acoustic characteristics of YA and OA speech produced in NORM, most likely linked to physiological factors. In challenging conditions, while OANH talkers typically patterned with YA talkers, OAHL talkers made adaptations more consistent with an increase in vocal effort. The study suggests that even mild presbycusis in healthy OAs can affect the speech adaptations made to maintain effective communication.

Speech adaptation to palatal perturbation: Evidence for sensorimotor reorganization across the workspace

Competent speakers demonstrate a high degree of precision in speech production, but also considerable flexibility in speech motor patterns used to attain speech goals. This flexibility is evident in studies examining adaptation to sensory perturbations, including physical manipulations that alter both auditory and somatosensory feedback (e.g., using a palatal prosthesis to disrupt the production of the alveolar fricative /s/). While the acoustic effects of such perturbations (and subsequent adaptation) have been well explored, their underlying articulatory basis remains poorly understood. In this study, we explored speech adaptation to a palatal perturbation in 9 adult speakers using acoustic and articulatory measures of adaptation (using electromagnetic articulography) during the production of various consonants and vowels. Acoustic measures showed effects of both the perturbation and subsequent compensation (following 15 minutes of speech practice) across the consonants and vowels. Analysis of tongue kinematics confirmed the global nature of these effects, including significant changes in sounds involving no physical interaction with the palate. Furthermore, directional analyses revealed a degree of fine-tuning in motor adaptation across phonemes. The findings indicate that even localized changes in palate shape induce complex compensatory changes in speech motor control across the articulatory workspace.

SEMANTIC TRANSFORMATION OF BIBLICAL PROTO-MESSAGES IN MODERN ENGLISH POLITICAL DISCOURSE

The article deals with the research of semantic transformation which Biblical proto-messages undergo in the process of their communicatively secondary realization in English political discourse. There have been singled out three groups of Biblical phraseological units which have different degree of adaptation in language and speech: phraseological units with the similar interpretation in all reference books, phraseological units which differ in shades of meaning in reference books and phraseological units which meaning differ completely in different reference books. The first group of Biblical phraseological units is characterized by the semantic homogeneity both in reference books and political speech. The analysis of the second group of Biblical phraseological units showed the absence of their complete semantic transformation in political discourse except for the widening of their evaluating connotative meaning and lexical transformation. Biblical phraseological units of the third group demonstrate either minimal semantic changes in political discourse or a complete deviation from its primary Biblical meaning, thus undergoing complete semantic transformation in political discourse.

Children's Acoustic and Linguistic Adaptations to Peers With Hearing Impairment.

This study aims to examine the clear speaking strategies used by older children when interacting with a peer with hearing loss, focusing on both acoustic and linguistic adaptations in speech. The Grid task, a problem-solving task developed to elicit spontaneous interactive speech, was used to obtain a range of global acoustic and linguistic measures. Eighteen 9- to 14-year-old children with normal hearing (NH) performed the task in pairs, once with a friend with NH and once with a friend with a hearing impairment (HI). In HI-directed speech, children increased their fundamental frequency range and midfrequency intensity, decreased the number of words per phrase, and expanded their vowel space area by increasing F1 and F2 range, relative to NH-directed speech. However, participants did not appear to make changes to their articulation rate, the lexical frequency of content words, or lexical diversity when talking to their friend with HI compared with their friend with NH. Older children show evidence of listener-oriented adaptations to their speech production; although their speech production systems are still developing, they are able to make speech adaptations to benefit the needs of a peer with HI, even without being given a specific instruction to do so. https://doi.org/10.23641/asha.6118817.

Application of Emotion Recognition and Modification for Emotional Telugu Speech Recognition

Majority of the automatic speech recognition systems (ASR) are trained with neutral speech and the performance of these systems are affected due to the presence of emotional content in the speech. The recognition of these emotions in human speech is considered to be the crucial aspect of human-machine interaction. The combined spectral and differenced prosody features are considered for the task of the emotion recognition in the first stage. The task of emotion recognition does not serve the sole purpose of improvement in the performance of an ASR system. Based on the recognized emotions from the input speech, the corresponding adapted emotive ASR model is selected for the evaluation in the second stage. This adapted emotive ASR model is built using the existing neutral and synthetically generated emotive speech using prosody modification method. In this work, the importance of emotion recognition block at the front-end along with the emotive speech adaptation to the ASR system models were studied. The speech samples from IIIT-H Telugu speech corpus were considered for building the large vocabulary ASR systems. The emotional speech samples from IITKGP-SESC Telugu corpus were used for the evaluation. The adapted emotive speech models have yielded better performance over the existing neutral speech models.

Rapid adaptation to foreign-accented speech and its transfer to an unfamiliar talker.

How fast can listeners adapt to unfamiliar foreign accents? Clarke and Garrett [J. Acoust. Soc. Am. 116, 3647-3658 (2004)] (CG04) reported that native-English listeners adapted to foreign-accented English within a minute, demonstrating improved processing of spoken words. In two web-based experiments that closely follow the design of CG04, the effects of rapid accent adaptation are examined and its generalization is explored across talkers. Experiment 1 replicated the core finding of CG04 that initial perceptual difficulty with foreign-accented speech can be attenuated rapidly by a brief period of exposure to an accented talker. Importantly, listeners showed both faster (replicating CG04) and more accurate (extending CG04) comprehension of this talker. Experiment 2 revealed evidence that such adaptation transferred to a different talker of a same accent. These results highlight the rapidity of short-term accent adaptation and raise new questions about the underlying mechanism. It is suggested that the web-based paradigm provides a useful tool for investigations in speech adaptation.

Speech Adaptation to Kinematic Recording Sensors: Perceptual and Acoustic Findings.

This study used perceptual and acoustic measures to examine the time course of speech adaptation after the attachment of electromagnetic sensor coils to the tongue, lips, and jaw. Twenty native English speakers read aloud stimulus sentences before the attachment of the sensors, immediately after attachment, and again 5, 10, 15, and 20 min later. They read aloud continuously between recordings to encourage adaptation. Sentence recordings were perceptually evaluated by 20 native English listeners, who rated 150 stimuli (which included 31 samples that were repeated to assess rater reliability) using a visual analog scale with the end points labeled as "precise" and "imprecise." Acoustic analysis began by segmenting and measuring the duration of the fricatives /s/ and /ʃ/ as well as the whole sentence. The spectral center of gravity and spectral standard deviation of the 2 fricatives were measured using Praat. These phonetic targets were selected because the standard placement of sensor coils on the lingual surface was anticipated to interfere with normal fricative production, causing them to become distorted. Perceptual ratings revealed a decrease in speech precision after sensor attachment and evidence of adaptation over time; there was little perceptual change beyond the 10-min recording. The spectral center of gravity for /s/ decreased, and the spectral standard deviation for /ʃ/ increased after sensor attachment, but the acoustic measures showed no evidence of adaptation over time. The findings suggest that 10 min may be sufficient time to allow speakers to adapt before experimental data collection with Northern Digital Instruments Wave electromagnetic sensors.

The role of rhythm in adaptation to dysrhythmic speech, continued

Rhythm cues have been shown to be important for deciphering speech in adverse listening conditions, even when the rhythm cues are corrupted. In an initial attempt to document the relationship between rhythm perception and processing of a naturally dysrhythmic speech signal, we found that listeners with expertise in rhythm perception were not advantaged with initial intelligibility of ataxic dysarthria but were significantly advantaged with adaptation to the degraded speech signal [Borrie, Lansford, and Barrett, Journal of Speech, Language, and Hearing Research, 60, 561–570 (2017)]. We speculated that listeners with skills in rhythm perception are better able to exploit experience (familiarization) with the degraded speech, learning something useful about corrupted rhythm cues for subsequent processing. This current study investigated whether the relationship between rhythm perception and perceptual adaptation of dysrhythmic speech, observed in our previous study with ataxic dysarthria, holds for other forms of dysrhythmic speech. Here, we replicate our original study with two different forms of dysarthria: the largely irregular and unpredictable speech of hyperkinetic dysarthria secondary to Huntington’s disease, and the relatively regular and predictable speech of hypokinetic dysarthric speech secondary to Parkinson’s disease. Results will bear on models of dysrhythmic speech perception as well as clinical practice.

Listener-adapted speech

Abstract While a significant amount of research has focussed on whether bilingualism bestows advantages in cognitive skills, perspective-taking and Theory of Mind, less is known about the effect of bilingualism in communicative tasks where these and related skills may be called for. This study examines bilingual and monolingual adults’ communicative skills through their production of two types of listener-adapted speech (LAS): child-directed speech and foreigner-directed speech. 20 monolinguals and 20 bilingual adults were asked to explain a cooking recipe to a child, a non-native adult and a control native adult. Participants adapted their speech for the child and the foreigner compared to the native adult. Furthermore, bilinguals adapted some features of their speech to a greater extent and in a fine-tuned way (wider pitch range addressing the child and vowel hyperarticulation addressing the foreigner). The prevalence of these features in bilingual speech was not correlated with personality or cognitive measures. We discuss possible sources of this difference in speech adaptation and implications for theories of bilingual cognition.

Inferring causes during speech perception

One of the central challenges in speech perception is the lack of invariance: talkers differ in how they map words onto the speech signal. Previous work has shown that one mechanism by which listeners overcome this variability is adaptation. However, talkers differ in how they pronounce words for a number of reasons, ranging from more permanent, characteristic factors such as having a foreign accent, to more temporary, incidental factors, such as speaking with a pen in the mouth. One challenge for listeners is that the true cause underlying atypical pronunciations is never directly known, and instead must be inferred from (often causally ambiguous) evidence. In three experiments, we investigate whether these inferences underlie speech perception, and how the speech perception system deals with uncertainty about competing causes for atypical pronunciations. We find that adaptation to atypical pronunciations is affected by whether the atypical pronunciations are seen as characteristic or incidental. Furthermore, we find that listeners are able to maintain information about previous causally ambiguous pronunciations that they experience, and use this previously experienced evidence to drive their adaptation after additional evidence has disambiguated the cause. Our findings revise previous proposals that causally ambiguous evidence is ignored during speech adaptation.

Abnormal Speech Motor Control in Individuals with 16p11.2 Deletions

Speech and motor deficits are highly prevalent (>70%) in individuals with the 600 kb BP4-BP5 16p11.2 deletion; however, the mechanisms that drive these deficits are unclear, limiting our ability to target interventions and advance treatment. This study examined fundamental aspects of speech motor control in participants with the 16p11.2 deletion. To assess capacity for control of voice, we examined how accurately and quickly subjects changed the pitch of their voice within a trial to correct for a transient perturbation of the pitch of their auditory feedback. When compared to controls, 16p11.2 deletion carriers show an over-exaggerated pitch compensation response to unpredictable mid-vocalization pitch perturbations. We also examined sensorimotor adaptation of speech by assessing how subjects learned to adapt their sustained productions of formants (speech spectral peak frequencies important for vowel identity), in response to consistent changes in their auditory feedback during vowel production. Deletion carriers show reduced sensorimotor adaptation to sustained vowel identity changes in auditory feedback. These results together suggest that 16p11.2 deletion carriers have fundamental impairments in the basic mechanisms of speech motor control and these impairments may partially explain the deficits in speech and language in these individuals.

Study of the Occurance of Labio-Palatine Cleft Embryogenic Disorders of the Stomatognated System by Using Lots of Wistar Rats Females

Labio-maxilo-palatine clefts are embryogenesis disorders of the stomatognathic system that occur due to the action of genetic or non-genetic factors in weeks 5-6 of intrauterine life. The clefts are part of the group of congenital malformations of the face. They appear from birth as a slit in the upper lip, hard palate and/or soft palate.Labio-maxilo-palatine cleafts are a current medical problem, especially regarding surgical recovery; they are congenital malformations of the face characterized by the absence of substance in the upper lip and/or in the palatine vault caused by the lack of fusion of labial and / or palatine buds during embryonic development.Simple labial cleft concerns only the lip, unlike the complete labial cleft which affects also the alveolar maxillary arch. In the case of this malformation, more serious than labial cleft, the cleft also affects the bone structures (the alveolar maxillary arche, the buccal palate) so that the oral cavity communicates with the nasal cavity and prevents sucking in infants. An early surgical recovery restores the integrity of anatomical structures, reestablishes disturbed functions, creates favorable conditions for speech education and social adaptation of the child according to age.The procedure is applied prior to the primary suture of the lip and of the anterior palate in order to minimize the dislocation of the segments of the maxillary arch. The correction of the malformation of the jaw arch in the case of bilateral clefts is much more difficult, but it has a greater importance due to the difficulty of reconstruction of the muscular plan and severe deformations, what will persist if the segments can not be aligned.In the bilateral clefts, the lateral segments are displaced medially, and the medial segment is protruding. The purpose of preoperative orthodontic treatment is to reposition the lateral segments so that the medial segment can be coaxed between them together as a vault key of the maxillary arch. In order to study the occurrence of labio-palatine cleft, we used eight groups of Wistar females rat, weighing between 200 and 250 grams. Each sample consists of 10 females rats. Most of the labial and palatine clefts are the result of multiple, genetic and non-genetic factors, each producing a minor developmental defect, called multifactorial heritage;It can be represented by a model in which responsibility for a disease is a variable caused by a combination of genetic and environmental factors. The therapeutic outcome depends on the complexity of the malformation, on the moment of surgery and on the selection of the most modern techniques and equipment suitable for the patient.

Do older and younger adult listeners show a “clear speech benefit” for speech produced by older adult talkers?

This study investigates whether a “clear speech benefit” is obtained for speech produced by older (OA) talkers and younger adult (YA) controls in a clear speaking style when heard in babble noise. The speech materials were recorded while OA and YA talkers read BKB sentences to a YA partner who repeated the sentence while hearing normally (NORM) or with a simulated hearing loss (HLS). The HLS condition naturally induced clear speech adaptations. 128 BKB sentences from 4 YA and 4 OA talkers (NORM, HLS) matched on a range of metrics were used in an adaptive listening test tracking the signal-to-noise ratio corresponding to 67% intelligibility. Listeners were 71 native British English listeners: 24 YA (M = 25.2 yrs), 27 OA-NH with normal hearing (M= 71.8), 20 OA-HL with presbyacusis (M= 73.7). Speech perception in noise was hardest for OA listeners, especially from OA-HL. SNR thresholds were significantly lower for YA than for OA voices. The clear speech benefit for HLS speech was only significant for YA voices for all listener groups. In summary, OA talkers were less intelligible than YA talkers regardless of listener age; clear speech adaptations by OA talkers did not result in enhanced intelligibility for OA or YA listeners.

Impaired Feedforward Control and Enhanced Feedback Control of Speech in Patients with Cerebellar Degeneration.

The cerebellum has been hypothesized to form a crucial part of the speech motor control network. Evidence for this comes from patients with cerebellar damage, who exhibit a variety of speech deficits, as well as imaging studies showing cerebellar activation during speech production in healthy individuals. To date, the precise role of the cerebellum in speech motor control remains unclear, as it has been implicated in both anticipatory (feedforward) and reactive (feedback) control. Here, we assess both anticipatory and reactive aspects of speech motor control, comparing the performance of patients with cerebellar degeneration and matched controls. Experiment 1 tested feedforward control by examining speech adaptation across trials in response to a consistent perturbation of auditory feedback. Experiment 2 tested feedback control, examining online corrections in response to inconsistent perturbations of auditory feedback. Both male and female patients and controls were tested. The patients were impaired in adapting their feedforward control system relative to controls, exhibiting an attenuated anticipatory response to the perturbation. In contrast, the patients produced even larger compensatory responses than controls, suggesting an increased reliance on sensory feedback to guide speech articulation in this population. Together, these results suggest that the cerebellum is crucial for maintaining accurate feedforward control of speech, but relatively uninvolved in feedback control.SIGNIFICANCE STATEMENT Speech motor control is a complex activity that is thought to rely on both predictive, feedforward control as well as reactive, feedback control. While the cerebellum has been shown to be part of the speech motor control network, its functional contribution to feedback and feedforward control remains controversial. Here, we use real-time auditory perturbations of speech to show that patients with cerebellar degeneration are impaired in adapting feedforward control of speech but retain the ability to make online feedback corrections; indeed, the patients show an increased sensitivity to feedback. These results indicate that the cerebellum forms a crucial part of the feedforward control system for speech but is not essential for online, feedback control.

Vowel generalization and its relation to adaptation during perturbations of auditory feedback.

Repeated perturbations of auditory feedback during vowel production elicit changes not only in the production of the perturbed vowel (adaptation) but also in the production of nearby vowels that were not perturbed (generalization). The finding that adaptation generalizes to other, nonperturbed vowels suggests that sensorimotor representations for vowels are not independent; instead, the goals for producing any one vowel may depend in part on the goals for other vowels. The present study investigated the dependence or independence of vowel representations by evaluating adaptation and generalization in two groups of speakers exposed to auditory perturbations of their first formant (F1) during different vowels. The speakers in both groups who adapted to the perturbation exhibited generalization in two nonperturbed vowels that were produced under masking noise. Correlation testing was performed to evaluate the relations between adaptation and generalization as well as between the generalization in the two nonperturbed vowels. These tests identified significant coupling between the F1 changes of adjacent vowels but not nonadjacent vowels. The pattern of correlation findings indicates that generalization was due in part to feedforward representations that are partly shared across adjacent vowels, possibly to maintain their acoustic contrast.NEW & NOTEWORTHY Speech adaptations to alterations, or perturbations, of auditory feedback have provided important insights into sensorimotor representations underlying speech. One finding from these studies that is yet to be accounted for is vowel generalization, which describes the effects of repeated perturbations to one vowel on the production of other vowels that were not perturbed. The present study used correlation testing to quantify the effects of changes in a perturbed vowel on neighboring (i.e., similar) nonperturbed vowels. The results identified significant correlations between the changes of adjacent, but not nonadjacent, vowel pairs. This finding suggests that generalization is partly a response to adaptation and not solely due to the auditory perturbation.

Learning a Talker or Learning an Accent: Acoustic Similarity Constrains Generalization of Foreign Accent Adaptation to New Talkers.

Past research has revealed that native listeners use top-down information to adjust the mapping from speech sounds to phonetic categories. Such phonetic adjustments help listeners adapt to foreign-accented speech. However, the mechanism by which talker-specific adaptation generalizes to other talkers is poorly understood. Here we asked what conditions induce crosstalker generalization in talker accent adaptation. Native-English listeners were exposed to Mandarin-accented words, produced by a single talker or multiple talkers. Following exposure, adaptation to the accent was tested by recognition of novel words in a task that assesses online lexical access. Crucially, test words were novel words and were produced by a novel Mandarin-accented talker. Results indicated that regardless of exposure condition (single or multiple talker exposure), generalization was greatest when the talkers were acoustically similar to one another, suggesting that listeners were not developing an accent-wide schema for Mandarin talkers, but rather attuning to the specific acoustic-phonetic properties of the talkers. Implications for general mechanisms of talker generalization in speech adaptation are discussed.

Speakers adapt speech based on percieved miscommunication

Recent work suggests that speakers can exaggerate their speech based on perceived communicative success (Buz et al., 2016). However, the flexibility and sophistication of this speech adaptation is relatively under-explored. We thus investigate whether this adaptation can be responsive to context-specific demands (e.g., exaggerating speech in contexts with increased potential for miscommunication), whether adaptation can target specific phonetic/acoustic properties (e.g., specifically exaggerating aspects of speech that may reduce miscommunication), and whether this adaptation involves inference about the potential causes of miscommunication. We investigate these questions in a web-based spoken communication game where we manipulate speakers' perceived communicative success. We find that speakers “smartly” adapt to miscommunication so as to increase speakers' likelihood of subsequent communicative success. The results argue for a speech production system that incorporates past experience and can adapt fine-grained properties of speech to better achieve communicative goals.

The Fetal Origin of the Human Chin

The chin prominence is a hallmark of the modern human face and bears on its labial surface an inverted-T bony relief. Evolutionarily, whether the human chin is an adaptation for mastication or speech is debated but there is little compelling data supporting either claim. Furthermore, some suggest that the inverted-T relief is more important for phylogenetic inference than the chin prominence. However, there is no evidence for the developmental independence of the inverted-T relief and chin prominence. This debate requires empirical data on fetal development of the human chin. Using 3D imaging of the musculo-cervico-craniofacial skeleton of human fetuses and geometric morphometric methods, we discovered a developmental sequence leading to a chin prominence during early fetal development that is very similar to that which we previously observed in postnatal modern humans and in chimpanzee fetuses. Furthermore, we provide the evidence that the inverted-T relief is developmentally integrated with the chin prominence. The evolution of the human chin is constrained by cervico-craniofacial developmental that maintain an unobstructed fetal airway. Finally, the inverted T-relief should be neither treated independently from the chin prominence in phylogenetic analysis, nor is it a relevant taxonomic trait that defines the symphysis of modern humans.