Ichiro Fujimoto

Measurement of temporal changes in vocal tract area function from 3D cine-MRI data.

A 3D cine-MRI technique was developed based on a synchronized sampling method [Masaki et al., J. Acoust. Soc. Jpn. E 20, 375-379 (1999)] to measure the temporal changes in the vocal tract area function during a short utterance /aiueo/ in Japanese. A time series of head-neck volumes was obtained after 640 repetitions of the utterance produced by a male speaker, from which area functions were extracted frame-by-frame. A region-based analysis showed that the volumes of the front and back cavities tend to change reciprocally and that the areas near the larynx and posterior edge of the hard palate were almost constant throughout the utterance. The lower four formants were calculated from all the area functions and compared with those of natural speech sounds. The mean absolute percent error between calculated and measured formants among all the frames was 4.5%. The comparison of vocal tract shapes for the five vowels with those from the static MRI method suggested a problem of MRI observation of the vocal tract: data from static MRI tend to result in a deviation from natural vocal tract geometry because of the gravity effect.

Dynamic Analysis of Articulatory Movement Using Magnetic Resonance Imaging Movies: Methods and Implications in Cleft Lip and Palate

Objectives To visualize articulatory movement using a magnetic resonance imaging (MRI) movie of a subject with cleft lip and palate (CLP) and to demonstrate the usefulness of this method for studying oropharyngeal function. Material and Methods Dynamic changes in oropharyngeal structures were assessed with an MRI movie of a man with cleft lip and palate and in a normal adult male volunteer during the articulation of /pa/, /ta/, and /ka/. Results and Conclusions Different movement patterns were observed during articulation in the subject with CLP compared with the normal volunteer. Posterosuperior movement of the tongue and the anterior movement of the posterior pharyngeal wall were clearly visualized in the subject with CLP. Thus, MRI movies appear to be a promising tool for evaluating speech function in patients with CLP because of their noninvasive and nonradiation nature.

Visualisation of hypopharyngeal cavities and vocal-tract acoustic modelling

The hypopharyngeal cavities consist of the laryngeal cavity and bilateral piriform fossa, constituting the bottom part of the vocal tract near the larynx. Visualisation of these cavities with magnetic resonance imaging (MRI) techniques reveals that during speech, the laryngeal cavity takes the form of a long-neck flask and the piriform fossa takes the form of a goblet of varying shapes: the former diminishes greatly in whispering and the latter disappears during deep inhalation. These cavities have been shown to exert significant acoustic effects at higher frequency spectra. In this study, acoustic experiments were conducted for male and female mechanical vocal tracts with the results that acoustic effects of those cavities determine the frequency spectra above 2 kHz, giving rise to peaks and zeros. An acoustic model of vowel production was proposed with three components: voice source, hypopharyngeal cavities and vocal tract proper, which provides effective means in controlling voice quality and expressing individual vocal characteristics.

Measurement of Hemodynamics of Auditory Cortex Using Magnetoencephalography and Near Infrared Spectroscopy

Near infrared (NIR) spectroscopy, a non-invasive optical method for monitoring hemodynamics, was applied to record evoked auditory response of the human brain. Our newly developed system detected the amount of oxygenated and deoxygenated hemoglobin in the area of the local brain located beneath the probes. In the study, we used magnetoencephalography (MEG) and NIR spectroscopy to observe the blood component change near the auditory cortex. The sound stimulus of 1 kHz sine wave at 70 dB SPL was used to elicit evoked responses in both experiments. The active region of the auditory cortex was determined by MEG, and the same area was examined by the NIR system. The results from the NIR experiments showed significant increases of total hemoglobin and deoxygenated hemoglobin, indicating that both blood flow and oxygen consumption at the cortical area increased in response to the sound stimuli. The NIR recordings at the two different depths revealed that the increases of local blood flow and oxygen consumption were observed at depths ranging between 20 and 30 mm from the scalp.

MRI observation of dynamic articulatory movements using a synchronized sampling method

The use of magnetic resonance imaging (MRI) in speech research has, typically, been limited to static, sustainable vocal tract configurations due to the long acquisition times required [e.g., Baer et al., J. Acoust. Soc. Am. 90, 799–828 (1991)]. This work describes the application of a synchronized MRI sampling technique developed for cardiac motion imaging to the visualization of dynamic articulatory movements. Subjects produced 128 repetitions of a target utterance (/tata/ and /kaka/) coincident with audible tone bursts synchronized with gating pulses controlling MRI scanning. During each repetition, 35 scans at 25‐ms intervals were acquired, each scan providing one row of frequency‐domain data for each of the 35 output frames. After repetitive scans were completed, the full sequence was processed to give a 40‐frames‐per‐second midsagittally oriented movie. Analysis of the resulting movies revealed that tongue shapes for the interconsonantal /a/ varied between the two utterance types, indicating a place...

An MRI-based analysis of the English /r/ and /l/ articulations

Midsagittal tongue shapes for sustained English /r/ and /l/ sounds between native speakers of American English (AE) and Japanese were compared using the magnetic resonance imaging (MRI) technique. The /r/ sound as produced by AE speakers was characterized by a constriction at the anterior part of the hard palate and the existence of a sublingual cavity, and for the /l/ sound, apical contact to the front teeth and/or alveolar ridge, and the absence of the sublingual cavity. For Japanese speakers, strategies to form the tongue shape contrast between /r/ and /l/ productions were categorized into four types depending on the type of contact/constriction and presence/absence of the sublingual cavity. The first type showed a pattern of tongue shape similar to AE speakers. The second and third types were characterized by /r/- and /l/-oriented production, respectively, for both sounds. In the last type, the distinction between /r/ and /l/ was formed only by the absence or presence of apical contact, while a sublingual cavity was produced for both sounds. These types are discussed in the context of a perceptual evaluation and an acoustical analysis.

Articulatory effects of vowel context on fricatives: A magnetic resonance image study

Magnetic resonance imaging (MRI) is increasingly used in speech production research, particularly to obtain three‐dimensional images of sustainable sounds such as fricatives or vowels. However, acoustic studies of fricatives [Shadle et al., Proc. ETRW, 193–196 (1996)] have shown that the spectral shape varies with vowel context, with the amount of variation depending on the fricative. This study, therefore, uses MRI to study the articulatory correlates of vowel context effects on fricatives. Two subjects (male French, female American English) for whom a large acoustic, aerodynamic, and articulatory database of fricatives already existed, were studied. Three different imaging methods were used that varied in acquisition time, image quality, and image extent: midsagittal turbo‐flash (2 s), midsagittal spin‐echo (15 s), and full coronal and axial spin‐echo scans (approx. 2 min each). The subjects uttered the fricatives [f, θ, s, ∫] in vowel contexts [a, i, u]. Results indicate that not only are vowel context...

An MRI study of the physiological mechanism of F0 lowering

The phenomena of F0 lowering in utterances, widely observed in a word accent or near a phrase boundary, is not sufficiently explained by the relaxation of F0 raising musculature, and the physiological mechanism for F0 lowering has been a question to be examined. Morphological observation of laryngeal framework was performed in this study using the magnetic resonance imaging (MRI) during phonation. Midsagittal images near the larynx were taken in different F0 levels in four male speakers. Relative positional changes among laryngeal components were measured to explore the chain of mechanisms that allows vocal fold shortening in low F0. In the results, vertical movements of the larynx were consistently observed to be correlated with F0 levels. Movements of the hyoid bone and changes in laryngeal cavity size were also found. A rotation of the cricoid cartilage was always associated with laryngeal descent towards lower F0. This rotation occurred to the direction of shortening the vocal folds, and its mechanism...