Michael Proctor

Real-time magnetic resonance imaging and electromagnetic articulography database for speech production research (TC)

USC-TIMIT is an extensive database of multimodal speech production data, developed to complement existing resources available to the speech research community and with the intention of being continuously refined and augmented. The database currently includes real-time magnetic resonance imaging data from five male and five female speakers of American English. Electromagnetic articulography data have also been presently collected from four of these speakers. The two modalities were recorded in two independent sessions while the subjects produced the same 460 sentence corpus used previously in the MOCHA-TIMIT database. In both cases the audio signal was recorded and synchronized with the articulatory data. The database and companion software are freely available to the research community.

Articulatory–acoustic kinematics: The production of American English /s/

Due to its aerodynamic, articulatory, and acoustic complexities, the fricative /s/ is known to require high precision in its control, and to be highly resistant to coarticulation. This study documents in detail how jaw, tongue front, tongue back, lips, and the first spectral moment covary during the production of /s/, to establish how coarticulation affects this segment. Data were obtained from 24 speakers in the Wisconsin x-ray microbeam database producing /s/ in prevocalic and pre-obstruent sequences. Analysis of the data showed that certain aspects of jaw and tongue motion had specific kinematic trajectories, regardless of context, and the first spectral moment trajectory corresponded to these in some aspects. In particular contexts, variability due to jaw motion is compensated for by tongue-tip motion and bracing against the palate, to maintain an invariant articulatory-aerodynamic goal, constriction degree. The change in the first spectral moment, which rises to a peak at the midpoint of the fricative, primarily reflects the motion of the jaw. Implications of the results for theories of speech motor control and acoustic-articulatory relations are discussed.

Paralinguistic mechanisms of production in human “beatboxing”: A real-time magnetic resonance imaging study

Real-time magnetic resonance imaging (rtMRI) was used to examine mechanisms of sound production by an American male beatbox artist. rtMRI was found to be a useful modality with which to study this form of sound production, providing a global dynamic view of the midsagittal vocal tract at frame rates sufficient to observe the movement and coordination of critical articulators. The subjects repertoire included percussion elements generated using a wide range of articulatory and airstream mechanisms. Many of the same mechanisms observed in human speech production were exploited for musical effect, including patterns of articulation that do not occur in the phonologies of the artists native languages: ejectives and clicks. The data offer insights into the paralinguistic use of phonetic primitives and the ways in which they are coordinated in this style of musical performance. A unified formalism for describing both musical and phonetic dimensions of human vocal percussion performance is proposed. Audio and video data illustrating production and orchestration of beatboxing sound effects are provided in a companion annotated corpus.

Pharyngeal articulation in the production of voiced and voiceless fricatives

A structural magnetic resonance imaging study has revealed that pharyngeal articulation varies considerably with voicing during the production of English fricatives. In a study of four speakers of American English, pharyngeal volume was generally found to be greater during the production of sustained voiced fricatives, compared to voiceless equivalents. Though pharyngeal expansion is expected for voiced stops, it is more surprising for voiced fricatives. For three speakers, all four voiced oral fricatives were produced with a larger pharynx than that used during the production of the voiceless fricative at the same place of articulation. For one speaker, pharyngeal volume during the production of voiceless labial fricatives was found to be greater, and sibilant pharyngeal volume varied with vocalic context as well as voicing. Pharyngeal expansion was primarily achieved through forward displacement of the anterior and lateral walls of the upper pharynx, but some displacement of the rear pharyngeal wall was also observed. These results suggest that the production of voiced fricatives involves the complex interaction of articulatory constraints from three separate goals: the formation of the appropriate oral constriction, the control of airflow through the constriction so as to achieve frication, and the maintenance of glottal oscillation by attending to transglottal pressure.

Improved imaging of lingual articulation using real-time multislice MRI

To develop a real‐time imaging technique that allows for simultaneous visualization of vocal tract shaping in multiple scan planes, and provides dynamic visualization of complex articulatory features.

An MRI Study of the Effect of Vowel Context on English Fricatives

To gain a better understanding of the long‐observed effects of vocalic context, the articulation of fricatives was investigated using Magnetic Resonance Imaging. Five speakers of American English were imaged while producing eight fricatives in the contexts [i‐a‐u‐schwa]. Sagittal, axial and oblique‐coronal volumes were acquired for each vowel‐fricative combination. Acoustic recordings were made during scans and separately in an anechoic chamber. Vocal tract models were generated by aligning and superimposing all three stack orientations. The models reveal that a variety of articulatory strategies are employed in the production of English fricatives, and that vocalic context is significant. For some subjects, tongue shape differs little with vowel context; other subjects show highly varied tongue shape differences but little difference in lip rounding. Two subjects show significant variation with vowel context for every fricative, including [θ]; two show very little difference, even for [f]. The sublingual...

Dynamic 3-D Visualization of Vocal Tract Shaping During Speech

Noninvasive imaging is widely used in speech research as a means to investigate the shaping and dynamics of the vocal tract during speech production. 3-D dynamic MRI would be a major advance, as it would provide 3-D dynamic visualization of the entire vocal tract. We present a novel method for the creation of 3-D dynamic movies of vocal tract shaping based on the acquisition of 2-D dynamic data from parallel slices and temporal alignment of the image sequences using audio information. Multiple sagittal 2-D real-time movies with synchronized audio recordings are acquired for English vowel-consonant-vowel stimuli /ala/, /ara/, /asa/, and /a∫a/. Audio data are aligned using mel-frequency cepstral coefficients (MFCC) extracted from windowed intervals of the speech signal. Sagittal image sequences acquired from all slices are then aligned using dynamic time warping (DTW). The aligned image sequences enable dynamic 3-D visualization by creating synthesized movies of the moving airway in the coronal planes, visualizing desired tissue surfaces and tube-shaped vocal tract airway after manual segmentation of targeted articulators and smoothing. The resulting volumes allow for dynamic 3-D visualization of salient aspects of lingual articulation, including the formation of tongue grooves and sublingual cavities, with a temporal resolution of 78 ms.

Articulatory comparison of Tamil liquids and stops using real‐time magnetic resonance imaging.

It has been hypothesized that liquid consonants differ from stops in that they exhibit more global control over tongue shapes. This has been demonstrated by ongoing work showing greater vowel context effects in the production of stops than liquids in Spanish and Russian. Languages with rich inventories of coronal consonants, like Tamil, provide an interesting challenge for this view, as the presence of retroflex‐dental contrasts among the stops may require substantial global tongue control, and therefore inhibit context effects. To test this, dynamic magnetic resonance imaging (MRI) was used to investigate the midsagittal production of Tamil liquids in intervocalic environments. MRI sequences were acquired at a frame rate of 22.4 Hz. The five liquids of Brahmin Tamil were elicited from three speakers in three different vowel contexts. Nasal stop consonants were also elicited at the same places of articulation to compare the influence of vocalic coarticulation on liquids and stops. Greater coarticulatory i...

Articulation of fricatives: Evidence from X‐ray microbeam data

Articulatory changes in /s/ over time give rise to the onset and offset of turbulence noise, but the small tolerances involved make it difficult to separately consider the effects of movement, phonetic context, and subject variation. Aerodynamic estimates of the constriction area have been shown to demonstrate a marked asymmetry, with the /s/ onset more rapid than offset [C. Scully, Speech Commun. 11, 1992]. Previous articulatory studies led us to expect an invariant tongue tip position, with jaw raising dependent somewhat on the following vowel. In order to investigate the timing of the constriction formation in fricatives, X‐ray microbeam data [Westbury et al., 1994] for citation forms of /sVd/ for 15 vowels were studied. In fact, the tongue marker patterns during [s] vary both by following vowel and subject; subjects seem to have different apical‐laminal strategies. The jaw reaches maximum height during [s] for each subject studied; that height does not appreciably vary with vowel. This indicates that ...

Characterizing Articulation in Apraxic Speech Using Real-Time Magnetic Resonance Imaging.

Purpose Real-time magnetic resonance imaging (MRI) and accompanying analytical methods are shown to capture and quantify salient aspects of apraxic speech, substantiating and expanding upon evidence provided by clinical observation and acoustic and kinematic data. Analysis of apraxic speech errors within a dynamic systems framework is provided and the nature of pathomechanisms of apraxic speech discussed. Method One adult male speaker with apraxia of speech was imaged using real-time MRI while producing spontaneous speech, repeated naming tasks, and self-paced repetition of word pairs designed to elicit speech errors. Articulatory data were analyzed, and speech errors were detected using time series reflecting articulatory activity in regions of interest. Results Real-time MRI captured two types of apraxic gestural intrusion errors in a word pair repetition task. Gestural intrusion errors in nonrepetitive speech, multiple silent initiation gestures at the onset of speech, and covert (unphonated) articulation of entire monosyllabic words were also captured. Conclusion Real-time MRI and accompanying analytical methods capture and quantify many features of apraxic speech that have been previously observed using other modalities while offering high spatial resolution. This patients apraxia of speech affected the ability to select only the appropriate vocal tract gestures for a target utterance, suppressing others, and to coordinate them in time.