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

The phonetic basis of phonological vowel nasality: Evidence from real-time MRI velum movement in German

It has been suggested that the development of contrastive vowel nasality in VN sequences may depend partly on the nature of the following consonant. In particular, there may be a preference for VN sequences preceding voiceless oral consonants to be phonologized due to aerodynamic constraints on velum height, resulting in temporal overlap of the vowel with a durationally constant velum gesture. We investigate the phonetic basis of this claim via direct imaging of velum kinematics in real-time MRI videos (50 fps) from 35 German speakers. The results show that, while the velum gesture does indeed begin and end earlier in /Vnt/ than in /Vnd/ sequences, the duration of the gesture itself is also shorter in this context. This suggests that increased temporal co-articulation in /Vnt/ sequences is not necessarily due to durational maintenance of the velum gesture, but to a temporally truncated velum gesture that is shifted in time

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

Real-time MRI of speaking at a resolution of 33 ms: Undersampled radial FLASH with nonlinear inverse reconstruction.

Dynamic MRI studies of the upper airway during speaking, singing or swallowing are complicated by the need for high temporal resolution and the presence of air-tissue interfaces that may give rise to image artifacts such as signal void and geometric distortions. This work exploits a recently developed real-time MRI technique to address these challenges for monitoring speech production at 3 T. The method combines a short-echo time radial FLASH MRI sequence (pulse repetition time/echo time = 2.22/1.44 ms; flip angle 5°) with pronounced undersampling (15 radial spokes per image) and image reconstruction by regularized nonlinear inversion. The resulting serial images at 1.5 mm in-plane resolution and 33.3 ms acquisition time are free of motion or susceptibility artifacts. This application focuses on a dynamic visualization of the main articulators during natural speech production (Standard Modern German). Respective real-time MRI movies at 30 frames per second clearly demonstrate the spatiotemporal coordination of lips, tongue, velum, and larynx for generating vowels, consonants, and coarticulations. The quantitative results for individual phonetic events are in agreement with previous non-MRI findings. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. Since the earliest studies of human articulation in the late 18th century, methods and applications have continuously been expanded. Nowadays, articulatory processes during speaking may be analyzed by a wide range of techniques including laryngoscopy and laryngography, electropalatography, electromyography, electromagnetic articulography, or imaging based on X-ray videofluoroscopy or sonography (1). However, while former approaches require an invasive procedure, which eventually disturbs the natural articulation of vowels and consonants, videofluoroscopy involves the exposure to radiation and sonography is restricted to specific image orientations. Although MRI promises noninvasive examinations as well as more flexible and detailed insights into the vocal tract, insufficient temporal resolution, and limited image quality still emerge as two major obstacles for studying speech production. For example, because long image acquisition times require either repetitively generated (2, 3) or continuant (4) speech sounds, such strategies preclude a proper visualization of the lips and tongue for plosive consonants that are characterized by rapid movements within 50–100 ms (5). In addition, motion-induced image blurring may result from data sharing when using long acquisitions with sliding-window reconstructions to achieve high frame rates (6, 7). It has therefore been concluded that the true temporal resolution for MRI should be comparable to that of standard videofluoroscopy, ideally no longer than 40 ms per image (8). Other problems are the occurrence of focal signal losses and geometric distortions that depend on the sensitivity of a chosen MRI acquisition technique to the unavoidable susceptibility differences near air-tissue interfaces in the upper airway (9, 10). Most recently, we have described a real-time MRI technique using highly undersampled radial FLASH with image reconstruction by regularized nonlinear inversion (11–13). Preliminary applications to cardiovascular function (14), quantitative blood flow (15), and normal swallowing (16) allow for serial real-time images (i.e., movies) with 1.5 to 2.0 mm in-plane resolution and 20–30 ms acquisition time. Accordingly, the purpose of this study was to exploit this real-time MRI method to address the challenges posed by dynamic MRI of speaking and to investigate the key articulatory configurations during natural speech production including vowels, consonants, and coarticulation effects in vowels preceded by consonants