Macrovibrissae and microvibrissae inversion and lateralization in elephants.

Elephants are known for strongly lateralized trunk behaviors, but the mechanisms driving elephant lateralization are poorly understood. Here, we investigate features of elephant mouth organization that presumably promote lateralization. We find the lower jaw of elephants is of narrow width, but is rostrally strongly elongated even beyond the jaw bone. Elephant lip vibrissae become progressively longer rostrally. Thus, elephants have two lateral dense, short microvibrissae arrays and central, less dense long macrovibrissae. This is an inversion of the ancestral mammalian facial vibrissae pattern, where central, dense short microvibrissae are flanked by two lateral macrovibrissae arrays. Elephant microvibrissae have smaller follicles than macrovibrissae. Similar to trunk-tip vibrissae, elephant lip microvibrissae show laterally asymmetric abrasion. Observations on Asian zoo elephants indicate lateralized abrasion results from lateralized feeding. It appears that the ancestral mammalian mouth (upper and lower lips, incisors, frontal microvibrissae) is shaped by oral food apprehension. The elephant mouth organization radically changed, however, because trunk-mediated feeding replaced oral apprehension. Such elephant mouth changes include the upper lip-nose fusion to the trunk, the super-flexible elongated lower jaw, the loss of incisors, and lateral rather than frontal microvibrissae. Elephants' specialization for lateral food insertion is reflected by the reduction in the centering effects of oral food apprehension and lip vibrissae patterns.

A data-efficient and easy-to-use lip language interface based on wearable motion capture and speech movement reconstruction.

Lip language recognition urgently needs wearable and easy-to-use interfaces for interference-free and high-fidelity lip-reading acquisition and to develop accompanying data-efficient decoder-modeling methods. Existing solutions suffer from unreliable lip reading, are data hungry, and exhibit poor generalization. Here, we propose a wearable lip language decoding technology that enables interference-free and high-fidelity acquisition of lip movements and data-efficient recognition of fluent lip language based on wearable motion capture and continuous lip speech movement reconstruction. The method allows us to artificially generate any wanted continuous speech datasets from a very limited corpus of word samples from users. By using these artificial datasets to train the decoder, we achieve an average accuracy of 92.0% across individuals (n = 7) for actual continuous and fluent lip speech recognition for 93 English sentences, even observing no training burn on users because all training datasets are artificially generated. Our method greatly minimizes users' training/learning load and presents a data-efficient and easy-to-use paradigm for lip language recognition.

Human lip vermilion: Physiology and age-related changes.

BACKGROUND: The human lip vermilion, also known as the red lip, is important to the quality of life and has long attracted the attention of cosmetic researchers. However, there is limited existing literature on the physiological characteristics and age-related alterations in the human vermilion. OBJECTIVE: We aim to provide an overview of the physiological characteristics and age-related alterations in the human vermilion. METHODS: This article is a result of previous research. We conducted a literature search using various academic databases such as Google Scholar, Web of Science, and PubMed. Our findings provided a comprehensive understanding of the physiological characteristics and age-related changes of the human lip vermilion. RESULTS: The human lip vermilion has a unique structure and physiological characteristics, and during the aging process, a few changes may occur in the human lip vermilion. CONCLUSION: Understanding the human lip vermilion's physiological characteristics and age-related changes can provide key information for the future innovation of lip vermilion care products. Further investigations are necessary to reach a consensus on the physiological characteristics and age-related alterations in the human vermilion.

Evaluation of oral function using a composite sensor during maximum lip closure and swallowing in normal children and adults.

BACKGROUND: There is growing interest in the development of objective methods for assessing lip-closing function in children. OBJECTIVE: To obtain normative data for healthy children in the developmental stages of lip closure function, we quantitatively evaluated oral movements associated with lip closure in children and adults using a composite sensor (CS). METHODS: Twenty-five normal children (11 boys, 14 girls) aged 8.8 ± 1.6 years and 25 young adults (13 men, 12 women) aged 27.4 ± 3.9 years were asked to perform test movements, maximal lip closure and swallowing of 3 mL of water. Lip-closing pressure (LP), intraoral baro-pressure (IP) and electromyographic (EMG) activity of the upper orbicularis oris muscle were simultaneously recorded using the CS. RESULTS: EMG activity of the upper orbicularis oris muscle during closure was significantly greater in adults than in children. There were significant positive correlations between integral values of LP and EMG for closure in adults (r = .527, p = .008) but not in children, and significant positive correlations between integral values of LP and IP for swallowing in children (r = .508, p = .010) but not in adults. CONCLUSIONS: The CS may provide an effective tool for evaluating lip function in children acquiring oral function. For the combination of maxillary orbicularis oculus contraction and formation of intraoral negative pressure, EMG activity of the upper orbicularis oris muscle involvement in LP and IP involvement in LP may differ between children and adults.

The Feel of Speech: Multisystem and Polymodal Somatosensation in Speech Production.

PURPOSE: The oral structures such as the tongue and lips have remarkable somatosensory capacities, but understanding the roles of somatosensation in speech production requires a more comprehensive knowledge of somatosensation in the speech production system in its entirety, including the respiratory, laryngeal, and supralaryngeal subsystems. This review was conducted to summarize the system-wide somatosensory information available for speech production. METHOD: The search was conducted with PubMed/Medline and Google Scholar for articles published until November 2023. Numerous search terms were used in conducting the review, which covered the topics of psychophysics, basic and clinical behavioral research, neuroanatomy, and neuroscience. RESULTS AND CONCLUSIONS: The current understanding of speech somatosensation rests primarily on the two pillars of psychophysics and neuroscience. The confluence of polymodal afferent streams supports the development, maintenance, and refinement of speech production. Receptors are both canonical and noncanonical, with the latter occurring especially in the muscles innervated by the facial nerve. Somatosensory representation in the cortex is disproportionately large and provides for sensory interactions. Speech somatosensory function is robust over the lifespan, with possible declines in advanced aging. The understanding of somatosensation in speech disorders is largely disconnected from research and theory on speech production. A speech somatoscape is proposed as the generalized, system-wide sensation of speech production, with implications for speech development, speech motor control, and speech disorders.

Relationship between texture perception and oral function: A preliminary study in young, healthy adults.

BACKGROUND: Oral frailty, characterised by reduced oral function, is associated with systemic health issues in older adults. Although the criteria for diminished oral function often focus on motor and secretory abilities, texture perception also plays a crucial role in health due to its impact on food intake and palatability. OBJECTIVE: This study aimed to explore the relationship between thickness discrimination ability (TDA) and oral motor and secretory functions in healthy young individuals. METHODS: Twenty-eight adults were assessed for texture perception using eight concentrations of aqueous xanthan gum solutions to determine TDA scores. Measurements of occlusal force, masticatory performance, tongue pressure, stimulated salivary flow rate and tongue-lip motor function were conducted. Spearman's correlation analysis was used to evaluate the relationship between TDA scores and oral functions. Participants were divided into high-sensitivity and low-sensitivity groups based on their TDA scores to compare oral function test results. RESULTS: The TDA scores varied among the participants, with higher scores correlating with higher masticatory performance (r = 0.41, p < .05). Masticatory performance in the high-sensitivity group was significantly higher than in the low-sensitivity group (211.9 ± 59.2 mg/dL vs. 157.9 ± 43.0 mg/dL, p = .013), with no significant differences in other oral functions. CONCLUSION: Masticatory performance was correlated with TDA, suggesting a link between the selection function of mastication and thickness discrimination. These findings highlight the potential relevance of texture perception in oral function and indicate the need for further exploration, particularly in older adults with declining oral health.

Evaluation of tongue pressure and lip closing force in bimaxillary orthognathic surgery: A retrospective study.

The purpose of this study was to quantitatively compare changes in tongue pressure and lip closing force among skeletal Class II and Class III patients, who had undergone orthognathic surgery, and a control group. Maximum tongue pressure and lip closing forces were measured preoperatively and at 6 and 12 months postoperatively. Time-course changes were analyzed and compared among the groups. The control group involved 40 skeletal Class I occlusion volunteers (20 male and 20 female), the Class II group involved 20 female patients, and the skeletal Class III group involved 40 patients, who were subdivided by sex into two groups comprising 20 males and 20 females, respectively. Time-course changes in tongue pressure were not significantly different between and within groups. However, postoperative lip closing forces became gradually higher in the Class III group female and male subjects compared with the control group, although this was not observed in the Class II group. There were significant correlations between tongue pressure and lip closing force before and after surgery (p = 0.001), and these correlations increased over time. Although there was no significant increase in maximum tongue pressure after orthognathic surgery, there was an associated increase in perioral muscle strength. This suggests that an increase in perioral muscle strength may contribute more to the stability of postoperative jaw morphology.

Measuring Articulatory Patterns in Amyotrophic Lateral Sclerosis Using a Data-Driven Articulatory Consonant Distinctiveness Space Approach.

PURPOSE: The aim of this study was to leverage data-driven approaches, including a novel articulatory consonant distinctiveness space (ACDS) approach, to better understand speech motor control in amyotrophic lateral sclerosis (ALS). METHOD: Electromagnetic articulography was used to record tongue and lip movement data during the production of 10 consonants from healthy controls (n = 15) and individuals with ALS (n = 47). To assess phoneme distinctness, speech data were analyzed using two classification algorithms, Procrustes matching (PM) and support vector machine (SVM), and the area/volume of the ACDS. Pearson's correlation coefficient was used to examine the relationship between bulbar impairment and the ACDS. Analysis of variance was used to examine the effects of bulbar impairment on consonant distinctiveness and consonant classification accuracies in clinical subgroups. RESULTS: There was a significant relationship between the ACDS and intelligible speaking rate (area, p = .003; volume, p = .010), and the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) bulbar subscore (area, p = .009; volume, p = .027). Consonant classification performance followed a consistent pattern with bulbar severity, where consonants produced by speakers with more severe ALS were classified less accurately (SVM = 75.27%; PM = 74.54%) than the healthy, asymptomatic, and mild-moderate groups. In severe ALS, area of the ACDS was significantly condensed compared to both asymptomatic (p = .004) and mild-moderate (p = .013) groups. There was no statistically significant difference in area between the severe ALS group and healthy speakers (p = .292). CONCLUSIONS: Our comprehensive approach is sensitive to early oromotor changes in response due to disease progression. The preserved articulatory consonant space may capture the use of compensatory adaptations to counteract influences of neurodegeneration. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.22044320.

Vocal Tract Resonance Detection at Low Frequencies: Improving Physical and Transducer Configurations.

Broadband excitation introduced at the speaker's lips and the evaluation of its corresponding relative acoustic impedance spectrum allow for fast, accurate and non-invasive estimations of vocal tract resonances during speech and singing. However, due to radiation impedance interactions at the lips at low frequencies, it is challenging to make reliable measurements of resonances lower than 500 Hz due to poor signal to noise ratios, limiting investigations of the first vocal tract resonance using such a method. In this paper, various physical configurations which may optimize the acoustic coupling between transducers and the vocal tract are investigated and the practical arrangement which yields the optimal vocal tract resonance detection sensitivity at low frequencies is identified. To support the investigation, two quantitative analysis methods are proposed to facilitate comparison of the sensitivity and quality of resonances identified. Accordingly, the optimal configuration identified has better acoustic coupling and low-frequency response compared with existing arrangements and is shown to reliably detect resonances down to 350 Hz (and possibly lower), thereby allowing the first resonance of a wide range of vowel articulations to be estimated with confidence.

Electromyographic activities of the jaw and facial muscles in subjects with different vertical skeletal patterns and breathing modes.

BACKGROUND: Mouth breathing (MB) can affect morphological changes in the craniofacial structures, electromyography is widely used for quantitative analysis of muscle function. OBJECTIVE: The aim was to evaluate the electromyographic (EMG) activities of the anterior temporalis (TA), masseter muscle (MM), orbicularis oris superior (OOS) and mentalis muscle (MT) in children with different vertical skeletal patterns and breathing modes during rest and various functional mandibular movements. METHODS: BioEMG III was used to measure the variations in EMG activities of TA, MM, OOS, and MT in 185 subjects aged 6-12 years during continuous clenching, rest, maximal intercuspation, lips closed lightly and swallowing. RESULTS: The results of logistic regression analysis showed that the model with vertical skeletal patterns as the dependent variable was ineffective (p = .106), while the model with breathing modes as the dependent variable was effective (p = .000). When considering both vertical skeletal patterns and breathing modes, the following significant differences were found. (1) In the normal-angle group, the EMG ratio in OOS with lips closed lightly of MB was significantly higher than NB (p = .005). (2) In the low-angle group, EMG ratios in TA and MM during the swallowing of MB were significantly lower than NB (p = .020, p = .040, respectively). (3) In the high-angle group, EMG ratios of MB were significantly higher in MT during continuous clenching, rest, lips closed lightly and swallowing (p = .038, p = .036, p = .005, p = .028, respectively), and OOS with lips closed lightly compared to NB (p = .005). CONCLUSION: Breathing modes and vertical skeletal patterns interacted to alter maxillofacial EMG activities, with breathing modes having a greater effect.

Magnetoencephalographic evaluation of repaired lip sensation in patients with cleft lip.

BACKGROUND: Cleft lip is the most common congenital anomaly worldwide. Nevertheless, lip somatosensory characteristics of patients with cleft lip after cheiloplasty have not yet been determined. The present study used magnetoencephalography to objectively evaluate the lip sensation in patients with unilateral cleft lip to establish a new objective evaluation method. METHODS: Participants were 15 patients with unilateral cleft lip after cheiloplasty (UCL group), and 30 healthy young subjects (control group). Five points of the upper and lower lips were stimulated electrically to measure somatosensory evoked magnetic fields (SEFs). The sources of the magnetic fields were modeled as single equivalent current dipoles (ECDs). ECDs located on the central sulcus by superimposition on magnetic resonance images were analyzed. Latency and intensity at 50-75 ms (cP60m) observed in the UCL group were compared with those in the control group. Thresholds of tactile stimuli in both groups were obtained using Semmes-Weinstein monofilaments for subjective sensory evaluation. RESULTS: No significant difference was found in the intensity of the cP60m or subjective evaluation between the groups. However, the latency of the cP60m was significantly longer in the upper lip of the UCL group than in the control group. CONCLUSIONS: SEFs showed a difference in lip sensation between the UCL group and the control group, suggesting that longer latency might be caused by the effects of surgical scarring on the neurotransmission pathway. These results suggest SEFs as useful for the objective evaluation of lip sensations. This study might improve future surgical procedures and lip functions of patients with cleft lip.

Lip-closing strength in children is enhanced by lip and facial muscle training.

OBJECTIVES: Weakening of lip-closing strength (LCS) associated with an incompetent lip seal (ILS) may affect the oral balance between the lip and tongue pressures. The purpose of this study was to evaluate the effects of lip-closing training in children with lower LCS and/or abnormal habits across different age groups and to compare its effects on increasing LCS in children with malocclusion and/or oral habits. MATERIAL AND METHODS: Lip-closing training was performed by 154 Japanese children aged 3-12 years using a specialized training device at home for 3 months. Children with oral habits and/or exhibiting less than standard LCS were included. LCS was measured using a digital strain force gauge at a dental clinic at the beginning (T0) and after each month (after 3 months: T3). RESULTS: Children had higher LCS responses after lip-closing training. The first month of lip-closing training was more effective than the subsequent months. With lip-closing training, the LCS increased from an average of 6.2 N (T0) to 11.4 N (T3) in Group I, 7.9 N (T0) to 12.8 N (T3) in Group II, and 6.8 N to 11.4 N in Group III. Anterior cross bite, including reverse bite, open bite, and tongue thrusting, significantly reduced training effects. CONCLUSION: Our findings showed that lower LCS in children with ILS resulted in greater responses to lip-closing training in a short period, but oral dysfunction, such as abnormal habits, inhibited the positive effects of training. Our results suggest that less detrimental effects of malocclusion and abnormal oral habits lip-closing training enhances LCS in younger children.

Comparing the Tongue and Lip Strength and Endurance of Children with Down Syndrome with Their Typical Peers Using IOPI.

Muscular hypotonia is a feature of Down syndrome (DS), and it affects the tongue and lips. A study on oral dysfunction in children with DS concluded that most of them did not have the tongue strength for completing the oral phase of swallowing. Recognizing the weakness of the oral muscles and improving its motor function positively affects mastication and swallowing, and prevents complications. This cross-sectional study aimed to measure the lip and tongue strength and endurance of children with DS and their typical peers, and compare these two groups with each other using Iowa Oral Performance Instrument (IOPI). Eight children with DS and 33 typical children aged 8-13 years were enrolled in this study. To examine the effect of age on the tongue strength and endurance, we divided the children into three groups of 8-9, 10-11, and 12-13 years old. The results showed that both anterior and posterior tongue strength were significantly lower in children with DS (p = 0.004 and 0.003). But, it was not the case with tongue endurance. Also, in 10-11 years old age group, the mean posterior tongue strength and in 12-13 years old age group the lip endurance was significantly lower in children with DS (p = 0.05 for both). Lips strength and endurance were both remarkably lower in children with DS (p = 0.004 and 0.02). In this study, tongue, and lip strength and endurance in both children with DS and typical ones were measured with IOPI for the first time. Moreover, it provided quantitative data on the strength and endurance of the muscles of the tongue and lips, which can contribute to future studies.

Do congruent lip movements facilitate speech processing in a dynamic audiovisual multi-talker scenario? An ERP study with older and younger adults.

In natural conversations, visible mouth and lip movements play an important role in speech comprehension. There is evidence that visual speech information improves speech comprehension, especially for older adults and under difficult listening conditions. However, the neurocognitive basis is still poorly understood. The present EEG experiment investigated the benefits of audiovisual speech in a dynamic cocktail-party scenario with 22 (aged 20-34 years) younger and 20 (aged 55-74 years) older participants. We presented three simultaneously talking faces with a varying amount of visual speech input (still faces, visually unspecific and audiovisually congruent). In a two-alternative forced-choice task, participants had to discriminate target words ("yes" or "no") among two distractors (one-digit number words). In half of the experimental blocks, the target was always presented from a central position, in the other half, occasional switches to a lateral position could occur. We investigated behavioral and electrophysiological modulations due to age, location switches and the content of visual information, analyzing response times and accuracy as well as the P1, N1, P2, N2 event-related potentials (ERPs) and the contingent negative variation (CNV) in the EEG. We found that audiovisually congruent speech information improved performance and modulated ERP amplitudes in both age groups, suggesting enhanced preparation and integration of the subsequent auditory input. In the older group, larger amplitude measures were found in early phases of processing (P1-N1). Here, amplitude measures were reduced in response to audiovisually congruent stimuli. In later processing phases (P2-N2) we found decreased amplitude measures in the older group, while an amplitude reduction for audiovisually congruent compared to visually unspecific stimuli was still observable. However, these benefits were only observed as long as no location switches occurred, leading to enhanced amplitude measures in later processing phases (P2-N2). To conclude, meaningful visual information in a multi-talker setting, when presented from the expected location, is shown to be beneficial for both younger and older adults.

Effects of adding a commercial capsaicin fertilizer on the feeding behavior of sika deer (Cervus nippon).

We investigated the inhibitory effect of capsaicin fertilizer on feeding in deer. We tested four captive adult female deer. In Experiment 1, in addition to the treatment (intact) containing only a solid feed (HC), we mixed the fertilizer not containing capsaicin (F) or the capsaicin fertilizer (CF) in the solid feed. In addition, the solid feed was put on a wire net that capsaicin fertilizer was placed 5 cm below (SCF). We investigated their feeding behavior response. In Experiment 2, we changed the amount of substance (fertilizer and capsaicin fertilizer) mixed in the HC. We mixed different amounts (0, 50, 100, and 200 g) of the treatments other than the intact with HC and presented them to the deer, and investigated their feeding behavior response. In Experiment 1, intake in the F and CF decreased (p < .05). In Experiment 2, HC intake was significantly lower in the 100 and 200 g CF (p < .05). However, HC intake relatively increased by the last day in the CF 200 g too. The capsaicin fertilizer decreased the feeding behavior of deer by directly touching the mucous membranes of the deer nose and lips. However, the effects were decreased over time.

Cortical reorganization following auditory deprivation predicts cochlear implant performance in postlingually deaf adults.

Long-term hearing loss in postlingually deaf (PD) adults may lead to brain structural changes that affect the outcomes of cochlear implantation. We studied 94 PD patients who underwent cochlear implantation and 37 patients who were MRI-scanned within 2 weeks after the onset of sudden hearing loss and expected with minimal brain structural changes in relation to deafness. Compared with those with sudden hearing loss, we found lower gray matter (GM) probabilities in bilateral thalami, superior, middle, inferior temporal cortices as well as the central cortical regions corresponding to the movement and sensation of the lips, tongue, and larynx in the PD group. Among these brain areas, the GM in the middle temporal cortex showed negative correlation with disease duration, whereas the other areas displayed positive correlations. Left superior, middle temporal cortical, and bilateral thalamic GMs were the most accurate predictors of post-cochlear implantation word recognition scores (mean absolute error [MAE] = 10.1, r = .82), which was superior to clinical variables used (MAE: 12.1, p < .05). Using the combined brain morphological and clinical features, we achieved the best prediction of the outcome (MAE: 8.51, r = .90). Our findings suggest that the cross-modal plasticity allowing the superior temporal cortex and thalamus to process other modal sensory inputs reverses the initially lower volume when deafness becomes persistent. The middle temporal cortex processing higher-level language comprehension shows persistent negative correlations with disease duration, suggesting this area's association with degraded speech comprehensions due to long-term deafness. Morphological features combined with clinical variables might play a key role in predicting outcomes of cochlear implantation.

Morphological and functional variability in central and subcentral motor cortex of the human brain.

There is a long-established link between anatomy and function in the somatomotor system in the mammalian cerebral cortex. The morphology of the central sulcus is predictive of the location of functional activation peaks relating to movement of different effectors in individuals. By contrast, morphological variation in the subcentral region and its relationship to function is, as yet, unknown. Investigating the subcentral region is particularly important in the context of speech, since control of the larynx during human speech production is related to activity in this region. Here, we examined the relationship between morphology in the central and subcentral region and the location of functional activity during movement of the hand, lips, tongue, and larynx at the individual participant level. We provide a systematic description of the sulcal patterns of the subcentral and adjacent opercular cortex, including the inter-individual variability in sulcal morphology. We show that, in the majority of participants, the anterior subcentral sulcus is not continuous, but consists of two distinct segments. A robust relationship between morphology of the central and subcentral sulcal segments and movement of different effectors is demonstrated. Inter-individual variability of underlying anatomy might thus explain previous inconsistent findings, in particular regarding the ventral larynx area in subcentral cortex. A surface registration based on sulcal labels indicated that such anatomical information can improve the alignment of functional data for group studies.

Analysis of Labial and Lingual Strength among Healthy Chinese Adults in Taiwan.

This study collected 11 parameters regarding the labial and lingual strength for maximum isometric and swallowing tasks among 150 healthy Chinese adults in Taiwan. Measurements were performed using the Iowa Oral Performance Instrument (IOPI). All of the labial and lingual strength parameters were measured three times. The maximal value of three trials represents the pressure of every parameter. The overall mean (±standard deviation) and maximum isometric pressures of the lips, anterior tongue, and posterior tongue were 24.81 ± 5.64, 55.95 ± 14.13, and 53.23 ± 12.24 kPa, respectively. The mean value of posterior tongue strength was less than that of the anterior tongue by approximately 5%. The percentages of maximum isometric tongue pressure during the swallowing of saliva and water were 85% and 80% for the anterior tongue and 90% and 81% for the posterior tongue, respectively. The average endurances for the anterior tongue and posterior tongue were 13.86 ± 7.08 and 10.06 ± 5.40 s, respectively. The maximum isometric pressures were greater than both the saliva and water swallowing pressures, and the saliva swallowing pressures were greater than the water swallowing pressures. A value of 33 kPa in maximum isometric pressure could serve as a demarcation of weak tongue strength for healthy Chinese adults. As for the repeated trials of labial and lingual strength, there were no statistically significant differences for any of the pressures obtained from the 11 labial and lingual strength parameters. The normative data can be used for the objective assessment of labial and lingual strength in healthy Chinese adults.

Quantal biomechanical effects in speech postures of the lips.

The unique biomechanical and functional constraints on human speech make it a promising area for research investigating modular control of movement. The present article illustrates how a modular control approach to speech can provide insights relevant to understanding both motor control and observed variation across languages. We specifically explore the robust typological finding that languages produce different degrees of labial constriction using distinct muscle groupings and concomitantly distinct lip postures. Research has suggested that these lip postures exploit biomechanical regions of nonlinearity between neural activation and movement, also known as quantal regions, to allow movement goals to be realized despite variable activation signals. We present two sets of computer simulations showing that these labial postures can be generated under the assumption of modular control and that the corresponding modules are biomechanically robust: first to variation in the activation levels of participating muscles, and second to interference from surrounding muscles. These results provide support for the hypothesis that biomechanical robustness is an important factor in selecting the muscle groupings used for speech movements and provide insight into the neurological control of speech movements and how biomechanical and functional constraints govern the emergence of speech motor modules. We anticipate that future experimental work guided by biomechanical simulation results will provide new insights into the neural organization of speech movements.NEW & NOTEWORTHY This article provides additional evidence that speech motor control is organized in a modular fashion and that biomechanics constrain the kinds of motor modules that may emerge. It also suggests that speech can be a fruitful domain for the study of modularity and that a better understanding of speech motor modules will be useful for speech research. Finally, it suggests that biomechanical modeling can serve as a useful complement to experimental work when studying modularity.