On the role of oral configurations in European Portuguese nasal vowels

The characterisation of nasal vowels is not only a question ofstudying velar aperture. Recent work shows that oropharyngeal articulatory adjustments enhance the acoustics of nasal couplingor, at least, magnify differences between oral/nasal vowel congeners. Despite preliminary studies on the oral configurations of nasal vowels, for European Portuguese, a quantitative analysis is missing, particularly one to be applied systematically to a desirably large number of speakers. The main objective ofthis study is to adapt and extend previous methodological advances for the analysis of MRI data to further investigate: howvelar changes affect oral configurations; the changes to the articulators and constrictions when compared with oral counteparts; and the closest oral counterpart. High framerate RT-MRIimages (50fps) are automatically processed to extract the vocal tract contours and the position/configuration for the different articulators. These data are processed by evolving a quantitative articulatory analysis framework, previously proposed by the authors, extended to include information regarding constrictions (degree and place) and nasal port. For this study, while the analysis of data for more speakers is ongoing, we considered a set of two EP native speakers and addressed the study of oral and nasal vowels mainly in the context of stop consonants

Analyzing speech in both time and space : generalized additive mixed models can uncover systematic patterns of variation in vocal tract shape in real-time MRI

We present a method of using generalized additive mixed models (GAMMs) to analyze midsagittal vocal tract data obtained from real-time magnetic resonance imaging (rt-MRI) video of speech production. Applied to rt-MRI data, GAMMs allow for observation of factor effects on vocal tract shape throughout two key dimensions: time (vocal tract change over the temporal course of a speech segment) and space (location of change within the vocal tract). Examples of this method are provided for rt-MRI data collected at a temporal resolution of 20 ms and a spatial resolution of 1.41 mm, for 36 native speakers of German. The rt-MRI data were quantified as 28-point semi-polar-grid aperture functions. Three test cases are provided as a way of observing vocal tract differences between: (1) /aː/ and /iː/, (2) /aː/ and /aɪ/, and (3) accentuated and unstressed /aː/. The results for each GAMM are independently validated using functional linear mixed models (FLMMs) constructed from data obtained at 20% and 80% of the vowel interval. In each case, the two methods yield similar results. In light of the method similarities, we propose that GAMMs are a robust, powerful, and interpretable method of simultaneously analyzing both temporal and spatial effects in rt-MRI video of speech

Planting the seed for sound change: Evidence from real-time MRI of velum kinematics in German

Velum movement signals generated from real-time magnetic resonance imaging videos of thirty-five German speakers were used to investigate the physiological conditions that might promote sound change involving the development of contrastive vowel nasality. The results suggest that, in comparison to when a nasal consonant precedes a voiced obstruent, the velum gesture associated with a nasal consonant preceding a voiceless obstruent undergoes gestural rescaling and temporal rephasing. This further suggests that the diachronic development of contrastive vowel nasality comprises two stages: the first stage involves gestural shortening and realignment, while the second stage involves a trading relationship between source and effect

Planting the seed of sound change: Evidence from real-time MRI of velum kinematics in German

Velum movement signals generated from real-time magnetic resonance imaging videos of thirty-five German speakers were used to investigate the physiological conditions that might pro-mote sound change involving the development of contrastive vowel nasality. The results suggest that, in comparison to when a nasal consonant precedes a voiced obstruent, the velum gesture as-sociated with a nasal consonant preceding a voiceless obstruent undergoes gestural rescaling and temporal rephasing. This further suggests that the diachronic development of contrastive vowel nasality comprises two stages: the first stage involves gestural shortening and realignment, while the second stage involves a trading relationship between source and effect

Modeling of oropharyngeal articulatory adaptation to compensate for the acoustic effects of nasalization

Hypernasality is one of the most detrimental speech disturbances that lead to declines of speech intelligibility. Velopharyngeal inadequacy, which is associated with anatomic defects such as cleft palate or neuromuscular disorders that affect velopharygneal function, is the primary cause of hypernasality. A simulation study by Rong and Kuehn [J. Speech Lang. Hear. Res. 55(5), 1438–1448 (2012)] demonstrated that properly adjusted oropharyngeal articulation can reduce nasality for vowels synthesized with an articulatory model [Mermelstein, J. Acoust. Soc. Am. 53(4), 1070–1082 (1973)]. In this study, a speaker-adaptive articulatory model was developed to simulate speaker-customized oropharyngeal articulatory adaptation to compensate for the acoustic effects of nasalization on /a/, /i/, and /u/. The results demonstrated that (1) the oropharyngeal articulatory adaptation effectively counteracted the effects of nasalization on the second lowest formant frequency (F2) and partially compensated for the effects of nasalization on vowel space (e.g., shifting and constriction of vowel space) and (2) the articulatory adaptation strategies generated by the speaker-adaptive model might be more efficacious for counteracting the acoustic effects of nasalization compared to the adaptation strategies generated by the standard articulatory model in Rong and Kuehn. The findings of this study indicated the potential of using oropharyngeal articulatory adaptation as a means to correct maladaptive articulatory behaviors and to reduce nasalit

Vowel height and velum position in German: Insights from a real-time magnetic resonance imaging study

Velum position was analysed as a function of vowel height in German tense and lax vowels preceding a nasal or oral consonant. Findings from previous research suggest an interdependence between vowel height and the degree of velum lowering, with a higher velum during high vowels and a more lowered velum during low vowels. In the current study, data were presented from 33 native speakers of Standard German who were measured via non-invasive high quality real-time magnetic resonance imaging. The focus was on exploring the spatiotemporal extent of velum lowering in tense and lax /a, i, o, ø/, which was done by analysing velum movement trajectories over the course of VN and VC sequences in CVNV and CVCV sequences by means of functional principal component analysis. Analyses focused on the impact of the vowel category and vowel tenseness. Data indicated that not only the position of the velum was affected by these factors but also the timing of velum closure. Moreover, it is argued that the effect of vowel height was to be better interpreted in terms of the physiological constriction location of vowels, i.e., the specific tongue position rather than phonetic vowel height

Rapid dynamic speech imaging at 3 Tesla using combination of a custom vocal tract coil, variable density spirals and manifold regularization

Purpose: To improve dynamic speech imaging at 3 Tesla. Methods: A novel scheme combining a 16-channel vocal tract coil, variable density spirals (VDS), and manifold regularization was developed. Short readout duration spirals (1.3 ms long) were used to minimize sensitivity to off-resonance. The manifold model leveraged similarities between frames sharing similar vocal tract postures without explicit motion binning. Reconstruction was posed as a SENSE-based non-local soft weighted temporal regularization scheme. The self-navigating capability of VDS was leveraged to learn the structure of the manifold. Our approach was compared against low-rank and finite difference reconstruction constraints on two volunteers performing repetitive and arbitrary speaking tasks. Blinded image quality evaluation in the categories of alias artifacts, spatial blurring, and temporal blurring were performed by three experts in voice research. Results: We achieved a spatial resolution of 2.4mm2/pixel and a temporal resolution of 17.4 ms/frame for single slice imaging, and 52.2 ms/frame for concurrent 3-slice imaging. Implicit motion binning of the manifold scheme for both repetitive and fluent speaking tasks was demonstrated. The manifold scheme provided superior fidelity in modeling articulatory motion compared to low rank and temporal finite difference schemes. This was reflected by higher image quality scores in spatial and temporal blurring categories. Our technique exhibited faint alias artifacts, but offered a reduced interquartile range of scores compared to other methods in alias artifact category. Conclusion: Synergistic combination of a custom vocal-tract coil, variable density spirals and manifold regularization enables robust dynamic speech imaging at 3 Tesla.Comment: 30 pages, 10 figure

Using naive listener imitations of native speaker productions to investigate mechanisms of listener-based sound change

This study was designed to test whether listener-based sound change-listener misperception (Ohala, 1981, 1993) and perceptual cue re-weighting (Beddor, 2009, 2012)-can be observed synchronically in a laboratory setting. Co-registered articulatory data (degree of nasalization, tongue height, breathiness) and acoustic data (F1 frequency) related to the productions of phonemic oral and nasal vowels of Southern French were first collected from four native speakers, and the acoustic recordings were subsequently presented to nine Australian English naive listeners, who were instructed to imitate the native productions. During these imitations, similar articulatory and acoustic data were collected in order to compare the articulatory strategies used by the two groups. The results suggest that the imitators successfully reproduced the acoustic distinctions made by the native speakers, but that they did so using different articulatory strategies. The articulatory strategies for the vowel pair /a/-/a/ suggest that listeners (at least partially) misperceived F1-lowering due to nasalization and breathiness as being due to tongue height. Additional evidence supports perceptual cue re-weighting, in that the naive imitators employed nasalance less, and tongue height more, in order to obtain the same F1 nasal-oral distinctions that the native speakers had originally produced

Spontaneous nasalization: An articulatory investigation of glottal consonants in Thai

Vowel nasalization usually occurs through a two-step process whereby a vowel is nasalized via coarticulation with a nearby nasal segment; when the language later drops the nasal segment, a nasal vowel remains. Spontaneous vowel nasalization is a rare, peculiar form of nasalization that emerges in contexts that lack an historical etymological nasal (Blevins and Garrett, 1992; Matisoff, 1975; Ohala, 1975, 1974). Spontaneous vowel nasalization has been found to emerge in contexts with glottal consonants, low vowels, and transitionally breathy segments such as fricatives and aspirates. Blevins and Garrett (1992) classified these contexts as rhinoglottophilia ‘nose-larynx-affinity’, rhinochthamalophilia ‘nose-low/flat-affinity’, and rhinosyrigmatophilia ‘nose-whistle-affinity’. Many articulatory and acoustic explanations have been proposed for spontaneous nasalization. First, vowels may nasalize near glottal consonants because they are underspecified for velopharyngeal opening and thus may be produced with a lowered velum. Second, low vowels may nasalize because they can better tolerate the acoustic consequences of greater nasal coupling; the intraoral acoustic impedance of low vowels is naturally lower. Finally, speakers may nasalize vowels in breathy environments through misperception or enhancement because nasality and breathiness are acoustically similar (Matisoff, 1975; Ohala and Amador, 1981). Due to the acoustic similarities between nasalization and breathiness, e.g. high spectral tilt and weakened F1, disentangling the relative roles of physiological nasalization and breathiness during spontaneous nasalization is not possible using acoustic data alone. There have been few articulatory investigations that assess the origins of spontaneous nasalization (Clumeck, 1975; Ohala, 1971). Thai arguably manifests an interaction among rhinoglottophilia, rhinochthamalophilia, and rhinosyrigmatophilia-based spontaneous nasalization. Thai is known to nasalize low and mid-low vowels after the voiceless glottal fricative /h/ and glottal stop /ʔ/, such that /hɛ˨/ [hɛ̃˨] ‘parade’ and /ʔaw˧/ [ʔãw˧] ‘to take’ are reported to sound nasal (Cooke, 1989; Matisoff, 1975; Noss, 1964). Vowels following /h/ are reportedly more susceptible to nasalization than those following /ʔ/ (Matisoff, 1975; Cooke, 1989). Furthermore, of the nasalized vowels, Cooke (1989) observed that /a/ is reported to sound more nasal than /ɛ/ and /ɔ/. In Thai it is possible that the velopharyngeal underspecification of glottal consonants, low tongue height, and breathy-nasal acoustic similarity (in proximity to /h/) may all play a role in nasalization. In order to deepen our understanding of these potentially interacting sources of spontaneous nasalization in Thai, this dissertation undertakes an extensive articulatory investigation of physiological nasalization and breathiness during spontaneously nasalized vowels in Central Thai. Spontaneous nasalization has been an historically difficult topic of study because its analysis requires a combination of articulatory data that measures both nasalization and phonation quality. This dissertation integrates measures from state-of-the-art ultra-fast magnetic resonance imaging (MRI), aerodynamics, and electroglottography (EGG) to estimate physiological nasalization and breathiness. The speech of ten speakers of Central Thai was assessed using these tools: Four speakers were recorded using ultra-fast MRI and six speakers were recorded using aerodynamics and EGG. Speakers produced CV syllables that varied by onset consonant and vowel height within the same carrier phrase. Syllables with an onset glottal consonant /h, ʔ/ were varied at four different vowel heights; syllables with onset consonants /n, th, d/ were included as nasal and oral controls. The major finding of this dissertation is that /h/-onset syllables are produced with greater physiological nasalization than /ʔ/-onset syllables. This finding suggests that, counter to previous claims that glottal consonants are generally underspecified for velopharyngeal opening in Thai, /ʔ/ is in fact specified, at least in a prosodically prominent context. Furthermore, using EGG we observed a slight increase in breathiness during vowels just after /h/, but not after /ʔ/, suggesting a potential relationship between nasalization and breathiness in Thai. The voiceless turbulence of /h/ induces coarticulatory breathiness during the following vowel; this breathiness may facilitate the perception of nasalization during the following vowel. This might explain why vowels after /h/ reportedly sound more nasal than vowels after /ʔ/ (Cooke, 1989; Matisoff, 1975). Further perceptual testing is needed to assess this possibility. Furthermore, we observed inconsistent and often minimal variation in physiological nasalization during vowels of varying height in both nasalized and non-nasal context. This suggests that spontaneous vowel nasalization in Central Thai may now be similar to Northeastern Thai, a dialect where all vowels were reported to nasalize after glottal consonants approximately 40 years ago (Matisoff, 1975). Finally, during /hV/ syllables, all /h/ consonants are produced with greater nasal airflow than the following vowel. The onset /h/ appears to be the locus of nasalization that spreads to the vowel through coarticulation. The results of this dissertation deepen our understanding of the production of spontaneous nasalization and contexts that facilitate its realization in Thai and perhaps crosslinguistically as well. Our results demonstrate that spontaneous nasalization in Thai is primarily attributed to rhinoglottophilia: velopharyngeal underspecification of onset /h/. Rhinosyrigmatophilia may potentially also play a role: the presence of breathiness after /h/ may enhance the percept of nasalization. Nasal coupling and breathiness may be integrated into a single acoustic object that the listener perceives as nasal. This possibility presents an intriguing example of the many-to-one problem, whereby many possible articulatory configurations may result in similar acoustic output (Maeda, 1990)