Robustness of lateral tongue bracing under bite block perturbation.

Lateral tongue bracing is a lingual posture in which the sides of the tongue are held against the palate and upper molars, and has been observed cross-linguistically. However, it is unknown whether lateral bracing makes adjustments to external perturbation like other body postures. The present study aims to test the robustness of lateral tongue bracing with three experiments. The first baseline experiment was an analysis of an electropalatogram database and the results showed lateral bracing being continuously maintained. The second experiment applied an external perturbation during speech production. A bite block was held between participants' teeth while intra-oral video was used to record contact between the sides of the tongue and upper molars during speech. The results indicated that lateral bracing was maintained most of the time during speech. The third experiment included simulations investigating the activation of tongue muscles relevant to lateral bracing at different degrees of jaw opening. The results show that bracing requires higher activation of bracing agonists and lower activation of bracing antagonists as jaw opening increases. Our results suggest that lateral tongue bracing is actively maintained and robust under external perturbation and further indicate it serves as an essential lingual posture during speech production.

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.

Do innate stereotypies serve as a basis for swallowing and learned speech movements?

Keven & Akins suggest that innate stereotypies like TP/R may participate in the acquisition of tongue control. This commentary examines this claim in the context of speech motor learning and biomechanics, proposing that stereotypies could provide a basis for both swallowing and speech movements, and provides biomechanical simulation results to supplement neurological evidence for similarities between the two behaviors.

Perceptual Integration of Visual Evidence of the Airstream from Aspirated Stops.

This study investigates whether indirect visual evidence of aspiration can influence speech perception as previously found for tactile information. Participants were shown video of a speaker producing the sequence "pom" and "bomb" in a noisy setting. In some tokens, a candle was visibly perturbed by aspiration. All participants were more likely to correctly identify "pom" and incorrectly identify "bomb" in the presence of visible perturbation, indicating that perceptual integration was taking place. This effect was stronger for participants who reported being consciously aware of the candle as a predictor. This indicates that ambient information can be incorporated in speech perception even when presented via an indirect modality, and that active attention can amplify this effect.

Talking while chewing: speaker response to natural perturbation of speech.

This study looks at how the conflicting goals of chewing and speech production are reconciled by examining the acoustic and articulatory output of talking while chewing. We consider chewing to be a type of perturbation with regard to speech production, but with some important differences. Ultrasound and acoustic measurements were made while participants chewed gum and produced various utterances containing the sounds /s/, /ʃ/, and /r/. Results show a great deal of individual variation in articulation and acoustics between speakers, but consistent productions and maintenance of relative acoustic distances within speakers. Although chewing interfered with speech production, and this interference manifested itself in a variety of ways across speakers, the objectives of speech production were indirectly achieved within the constraints and variability introduced by individual chewing strategies.