Using ultrasound and nasalance to separate oral and nasal contributions to formant frequencies of nasalized vowels

Sound Visualization Demonstrates Velopharyngeal Coupling and Complex Spectral Variability in Asian Elephants

Sound production mechanisms set the parameter space available for transmitting biologically relevant information in vocal signals. Low-frequency rumbles play a crucial role in coordinating social interactions in elephants' complex fission-fusion societies. By emitting rumbles through either the oral or the three-times longer nasal vocal tract, African elephants alter their spectral shape significantly. In this study, we used an acoustic camera to visualize the sound emission of rumbles in Asian elephants, which have received far less research attention than African elephants. We recorded nine adult captive females and analyzed the spectral parameters of 203 calls, including vocal tract resonances (formants). We found that the majority of rumbles (64%) were nasally emitted, 21% orally, and 13% simultaneously through the mouth and trunk, demonstrating velopharyngeal coupling. Some of the rumbles were combined with orally emitted roars. The nasal rumbles concentrated most spectral energy in lower frequencies exhibiting two formants, whereas the oral and mixed rumbles contained higher formants, higher spectral energy concentrations and were louder. The roars were the loudest, highest and broadest in frequency. This study is the first to demonstrate velopharyngeal coupling in a non-human animal. Our findings provide a foundation for future research into the adaptive functions of the elephant acoustic variability for information coding, localizability or sound transmission, as well as vocal flexibility across species.

Bengali nasal vowels: lexical representation and listener perception

This paper focuses on the question of the representation of nasality as well as speakers' awareness and perceptual use of phonetic nasalisation by examining surface nasalisation in two types of vowels in Bengali: underlying nasal vowels (CṼC) and nasalised vowels before a nasal consonant (CVN). A series of three cross-modal forced-choice experiments was used to investigate the hypothesis that only unpredictable nasalisation is stored and that this sparse representation governs how listeners interpret vowel nasality. Visual full-word targets were preceded by auditory primes consisting of CV segments of CVC words with nasal vowels ([tʃɑ̃] for [tʃɑ̃d] 'moon'), oral vowels ([tʃɑ] for [tʃɑl] 'unboiled rice') or nasalised oral vowels ([tʃɑ̃(n)] for [tʃɑ̃n] 'bath') and reaction times and errors were measured. Some targets fully matched the prime while some matched surface or underlying representation only. Faster reaction times and fewer errors were observed after CṼC primes compared to both CVC and CVN primes. Furthermore, any surface nasality was most frequently matched to a CṼC target unless no such target was available. Both reaction times and error data indicate that nasal vowels are specified for nasality leading to faster recognition compared to underspecified oral vowels, which cannot be perfectly matched with incoming signals.

Articulatory Evidence for the Syllable-final Nasal Merging in Taiwan Mandarin

Syllable-final nasals /n/ and /ŋ/ in Taiwan Mandarin have been reported to be undergoing merging. Perceptual studies have reported that the alleged merging is context-sensitive and the merging directions are vowel-dependent. These findings have been mostly attributed to dialectal and social factors. The current study uses ultrasonography to capture postures of the entire tongue during the production of syllable-final nasals. The results, though confirming previous findings that the merging directions of syllable-final nasals are vowel-dependent, are best accounted for by the biomechanics of the tongue, as supported by computational 3D model simulations. Furthermore, for some speakers, although nasals were merged in terms of tongue posture, the degrees of nasalization of the preceding vowel were contrastive, suggesting that the merging process may be incomplete.

A practical method of estimating the time-varying degree of vowel nasalization from acoustic features

This paper presents a simple and easy-to-use method of creating a time-varying signal of the degree of nasalization in vowels, generated from acoustic features measured in oral and nasalized vowel contexts. The method is presented for separate models constructed using two sets of acoustic features: (1) an uninformed set of 13 Mel-frequency cepstral coefficients (MFCCs) and (2) a combination of the 13 MFCCs and a phonetically informed set of 20 acoustic features of vowel nasality derived from previous research. Both models are compared against two traditional approaches to estimating vowel nasalization from acoustics: A1-P0 and A1-P1, as well as their formant-compensated counterparts. Data include productions from six speakers of different language backgrounds, producing 11 different qualities within the vowel quadrilateral. The results generated from each of the methods are compared against nasometric measurements, representing an objective "ground truth" of the degree of nasalization. The results suggest that the proposed method is more robust than conventional acoustic approaches, generating signals which correlate strongly with nasometric measures across all vowel qualities and all speakers and accurately approximate the time-varying change in the degree of nasalization. Finally, an experimental example is provided to help researchers implement the method in their own study designs.

An acoustic camera approach to studying nasality in speech: The case of Polish nasalized vowels

The purpose of this research is to introduce an acoustic camera method to analyze nasality in speech. The input information is generated using an acoustic camera device composed of a 16-channel audio recorder with a microphone array, a high-speed video camera, and Carstens articulograph (model AG500). The linearly constrained minimum variance algorithm is used to provide illustrations of the spatial acoustic field distribution. Acoustic pressure distribution is determined as related to the location of oral, nasal, and oronasal resonances, as well as the root mean square value of the pressure. Durations of particular types of resonances activated in the course of speech sound production are also specified. An example application of the method is discussed for Polish nasalized vowels. The internal structure of the vowels is heterogeneous and involves alternate or simultaneous activation of oral and nasal resonances. The order of appearance of these resonances and their percentage share in the realization of the vowels is determined based on the spatial distribution of the acoustic field. The vowels' structure is demonstrated to be even more complex than suggested in former studies. Furthermore, the proportion of nasality is found to vary significantly between the vowels [ɛ w ̃ ] and [ɔ w ̃ ].

Three-dimensional printable ultrasound transducer stabilization system

When using ultrasound imaging of the tongue for speech recording/research, submental transducer stabilization is required to prevent the ultrasound transducer from translating or rotating in relation to the tongue. An iterative prototype of a lightweight three-dimensional-printable wearable ultrasound transducer stabilization system that allows flexible jaw motion and free head movement is presented. The system is completely non-metallic, eliminating interference with co-recorded signals, thus permitting co-collection and co-registration with articulometry systems. A motion study of the final version demonstrates that transducer rotation is limited to 1.25° and translation to 2.5 mm-well within accepted tolerances.