Christopher Carignan

Managing the distinctiveness of phonemic nasal vowels: Articulatory evidence from Hindi

There is increasing evidence that fine articulatory adjustments are made by speakers to reinforce and sometimes counteract the acoustic consequences of nasality. However, it is difficult to attribute the acoustic changes in nasal vowel spectra to either oral cavity configuration or to velopharyngeal opening (VPO). This paper takes the position that it is possible to disambiguate the effects of VPO and oropharyngeal configuration on the acoustic output of the vocal tract by studying the position and movement of the tongue and lips during the production of oral and nasal vowels. This paper uses simultaneously collected articulatory, acoustic, and nasal airflow data during the production of all oral and phonemically nasal vowels in Hindi (four speakers) to understand the consequences of the movements of oral articulators on the spectra of nasal vowels. For Hindi nasal vowels, the tongue body is generally lowered for back vowels, fronted for low vowels, and raised for front vowels (with respect to their oral congeners). These movements are generally supported by accompanying changes in the vowel spectra. In Hindi, the lowering of back nasal vowels may have originally served to enhance the acoustic salience of nasality, but has since engendered a nasal vowel chain shift.

Compensatory articulation in American English nasalized vowels

Abstract In acoustic studies of vowel nasalization, it is sometimes assumed that the primary articulatory difference between an oral vowel and a nasal vowel is the coupling of the nasal cavity to the rest of the vocal tract. Acoustic modulations observed in nasal vowels are customarily attributed to the presence of additional poles affiliated with the naso-pharyngeal tract and zeros affiliated with the nasal cavity. We test the hypothesis that oral configuration may also change during nasalized vowels, either enhancing or compensating for the acoustic modulations associated with nasality. We analyze tongue position, nasal airflow, and acoustic data to determine whether American English /i/ and /a/ manifest different oral configurations when they are nasalized, i.e. when they are followed by nasal consonants. We find that tongue position is higher during nasalized [ĩ] than it is during oral [i] but do not find any effect for nasalized [a]. We argue that speakers of American English raise the tongue body during nasalized [ĩ] in order to counteract the perceived F1-raising (centralization) associated with high vowel nasalization.

A comparison of acoustic and articulatory methods for analyzing vowel differences across dialects: Data from American and Australian English

In studies of dialect variation, the articulatory nature of vowels is sometimes inferred from formant values using the following heuristic: F1 is inversely correlated with tongue height and F2 is inversely correlated with tongue backness. This study compared vowel formants and corresponding lingual articulation in two dialects of English, standard North American English, and Australian English. Five speakers of North American English and four speakers of Australian English were recorded producing multiple repetitions of ten monophthongs embedded in the /sVd/ context. Simultaneous articulatory data were collected using electromagnetic articulography. Results show that there are significant correlations between tongue position and formants in the direction predicted by the heuristic but also that the relations implied by the heuristic break down under specific conditions. Articulatory vowel spaces, based on tongue dorsum position, and acoustic vowel spaces, based on formants, show systematic misalignment due in part to the influence of other articulatory factors, including lip rounding and tongue curvature on formant values. Incorporating these dimensions into dialect comparison yields a richer description and a more robust understanding of how vowel formant patterns are reproduced within and across dialects.

The articulatory dynamics of pre-velar and pre-nasal /æ/-raising in English: An ultrasound studya)

Most dialects of North American English exhibit /æ/-raising in some phonological contexts. Both the conditioning environments and the temporal dynamics of the raising vary from region to region. To explore the articulatory basis of /æ/-raising across North American English dialects, acoustic and articulatory data were collected from a regionally diverse group of 24 English speakers from the United States, Canada, and the United Kingdom. A method for examining the temporal dynamics of speech directly from ultrasound video using EigenTongues decomposition [Hueber, Aversano, Chollet, Denby, Dreyfus, Oussar, Roussel, and Stone (2007). in IEEE International Conference on Acoustics, Speech and Signal Processing (Cascadilla, Honolulu, HI)] was applied to extract principal components of filtered images and linear regression to relate articulatory variation to its acoustic consequences. This technique was used to investigate the tongue movements involved in /æ/ production, in order to compare the tongue gestures involved in the various /æ/-raising patterns, and to relate them to their apparent phonetic motivations (nasalization, voicing, and tongue position).

Understanding the relationship between acoustics and articulation of nasal and oral vowels

While real-time magnetic resonance imaging (rt-MRI) provides high spatiotemporal resolution for speech research, the associated audio is noisy, presenting a challenge for research on the relationship between articulation and the acoustic signal and solving the articulatory inversion problem. Using state-of-the-art denoising methods, the current study denoised rt-MRI audio associated with nasal and oral French vowels produced by one speaker, and extracted F1-3 from the midpoints of each vowel for /a, o, e/ and their nasal counterparts. Oblique images were taken of the velopharyngeal port at 25 frames/second, and average pixel intensity (API) in the velopharyngeal region was taken from images corresponding to the vowel midpoint. General additive models showed a significant relationship between API and F1 for oral and nasal vowels. (Lower API indicates a wider velopharyngeal opening.) F1 of /a/ was lower than /a/, while F1 was higher in the nasal /o/ and /ẽ/ than their oral counterparts, all of which are exp...

Using ultrasound articulatory signals to investigate the phonetic motivations of English /æ/ tensing

A common simplifying technique in ultrasound studies of variation is to select a single representative frame for each token, sacrificing dynamic information that is often critical for understanding the phonetic motivations of phonological phenomena. We examine the phonetic motivations for tongue body raising in English /ae/ tensing (e.g., Labov et al. 2005) in 23 North American English speakers using phonetically meaningful time-varying articulatory signals extracted directly from ultrasound video. An articulatory measure of /ae/ tenseness is generated using regression to find the linear combination of articulatory principal components (found using EigenTongue Feature Extraction; Hueber et al. 2007) that best accounts for the F2-F1 difference in front vowels. We have previously shown (Carignan et al. 2015) that tensing before /m n/ involves tongue body raising that is timed to the vowel nucleus, whereas tensing before /ɡ ŋ/ involves anticipating the velar closure to different degrees in different dialects. ...

A study of tongue trajectories for English /æ/ using articulatory signals automatically extracted from lingual ultrasound video

While ultrasound imaging has made articulatory phonetics more accessible, quantitative analysis of ultrasound data often reduces speech sounds to tongue contours traced from single video frames, disregarding the temporal aspect of speech. We propose a tracing-free method for directly converting entire ultrasound videos to phonetically interpretable articulatory signals using Principal Component Analysis of image data (Hueber et al. 2007). Once a batch of ultrasound images (e.g., 36,000 frames from 10 min at 60 fps) has been reduced to 20 principal components, numerous techniques are available for deriving temporally changing articulatory signals that are both phonetically meaningful and comparable across speakers. Here we apply a regression model to find the linear combination of PCs that is the lingual articulatory analog of the front diagonal of the acoustic vowel space (Z2-Z1). We demonstrate this technique with a study of /ae/ tensing in 20 speakers of North American English varieties with different te...