Satoru Fujita

Japan Advanced Institute of Science and Technology, KMQ, Ishikawa, Japan

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Publications (10)6.02 Total impact

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    ABSTRACT: 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.
    Full-text · Article · Aug 2010 · Computer Methods in Biomechanics and Biomedical Engineering
  • Qiang Fang · Satoru Fujita · Xugang Lu · Jianwu Dang
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    ABSTRACT: Muscle activations during speech production are important for understanding speech motor control. In this paper, we put forward a physiological articulatory model-based approach to estimate muscle activations in producing five sustained Japanese vowels by minimizing the morphological difference between model simulations and target MRI observations, where the model is an improved version of Dang's partial 3D model. The initial muscle activations in the model simulation are set according to observation obtained by EMG measurement in producing vowels [6]. Then, the activation level of the tongue muscles are gradually adjusted so as to reduce the difference between the simulations and target MRI observations using an optimization approach. The results show that the proposed method can provide more details of the muscle activations than that obtained by EMG. In addition, the results suggest that the muscles Transversus and Verticalis play important roles in manipulating the length of tongue for vowel production; and, it is better to separate the Styloglossus into two control units, the anterior portion and posterior portion, in vowel production.
    No preview · Article · Jan 2009 · Acoustical Science and Technology
  • Qiang Fang · Satoru Fujita · Xugang Lu · Jianwu Dang
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    ABSTRACT: Muscle activations in speech production are important for understanding speech control. To overcome the problems of previous methods, we proposed a physiological articulatory model based approach to explore the muscle activations in the production of the five sustained Japanese vowels through an optimization procedure which minimizes the morphological differences between the model simulations and MRI observations. The general findings were consistent with the observations obtained using EMG. In addition, we found that the Transversus and Verticalis actively participate in vowel production. This implies the proposed method is appropriate for estimating the muscle activation patterns during vowels production.
    No preview · Conference Paper · Jan 2008
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    Satoru Fujita · Jianwu Dang · Noriko Suzuki · Kiyoshi Honda
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    ABSTRACT: The tongue possesses a complex muscular structure, and its motor functions are also intricate. Therefore, it would be beneficial to use a computational physiological model of the tongue to examine its vital functions in normal and pathological conditions. Thus far, the studies of tongue models have focused on symmetric movements for normal speech. For clinical purposes, it is necessary to develop a physiological model to deal with daily vital activities such as mastication and swallowing. To do so, we constructed a full 3D physiological model of the tongue based on MRI data from a normal subject, and verified the basic functions of the model based on anatomic and physiological knowledge. In this study, the model was applied to clinical issues: prediction and verification of the changes in movements of the tongue with a tumor before and after partial glossectomy, respectively. Tongue protrusion and lateral bending motion were examined for the prediction and verification. The simulation results were consistent with the observations for a patient with a tumor in the tongue. Comparisons of the simulation and observation in the clinical case showed that the model could predict potential effects of the glossectomy on the tongue movements. It is suggested that the model is a useful tool for pre-operative planning of glossectomy.
    Preview · Article · Nov 2007 · International Journal of Oral Science
  • Xugang Lu · Jianwu Dang · Satoru Fujita

    No preview · Article · Jan 2007 · The Journal of the Acoustical Society of America
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    Satoru Fujita · Jianwu Dang · Noriko Suzuki · Kiyoshi Honda
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    ABSTRACT: Simulation techniques using 2D or 3D tongue models have been adopted in investigating mechanisms of speech production. However, large asymmetric deformations of the tongue have not been challenged yet for both normal and pathologic cases. In this study, a full 3D tongue model was constructed by extending an existing partial 3D model, and it is used to perform large asymmetric 3D deformations to generate tongue gestures with bending and torsion. Furthermore, simulations of a hemi-laterally reconstructed tongue demonstrated tongue protrusion with a bending motion, as often observed in real pathological cases. These results confirmed that the proposed tongue model performed behaviors of normal and pathological tongues and that this model can be a useful tool for the study of speech disorders with pathology of the tongue.
    Full-text · Article · Jan 2006
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    Jianwu Dang · Satoru Fujita · Emi Murano · Maureen Stone
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    ABSTRACT: To develop a physiological articulatory model for speech production, mastication and swallowing, we proposed an analysis-by-synthesis (AbS) based estimation method for investigating contributions of the tongue muscles in both exterior movement and interior deformation using observations and model simulations. The validity of the method was confirmed by comparing the estimated muscle activation to known muscle activation via model simulation using a full three dimensional physiological articulatory model. Observations were conducted to measure several simple tasks of large-scale tongue deformations using tagged magnetic resonance imaging (tMRI), and the principal strain of the deformations were analyzed using HARP MRI analysis. The muscle activation was examined based on the principal strain pattern and anatomic knowledge. According to the observation, a muscle activation pattern was designed to generate a tongue movement with extreme protrusion-retraction using the model. Muscle activation in the movement was estimated by comparing the principal strain pattern and known muscle forces. The model simulation and tMRI observation showed consistent strain patterns with each other. Thestudy showed that the muscle activation within tongue movement is able to be estimated from local deformationsusing the AbS method.
    Full-text · Article · Jan 2006
  • Satoru Fujita · Kiyoshi Honda
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    ABSTRACT: Solid models of the vocal tract with hypopharyngeal cavities were molded with a stereolithographic technique based on MRI data obtained from a male speaker during the production of Japanese vowels /a/ and /o/. A vowel synthesis experiment conducted with the models revealed a relatively good agreement in the second and third formants, as well as in anti-resonance at 4-5 kHz. The elimination of the models' piriform fossa resulted in the disappearance of the anti-resonance and shifts of the adjacent formants. The modification of the laryngeal cavity into a uniform tube caused spectral changes in the frequency range of 1.5-7.0 kHz. These acoustic effects of hypopharyngeal cavities were dependent on vocal tract shapes.
    No preview · Article · Jul 2005 · Acoustical Science and Technology
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    ABSTRACT: Recent investigations using magnetic resonance imaging (MRI) of human speech organs have opened up new avenues of research. Visualization of the speech production system provides abundant information on the physiological and acoustic realization of human speech. This article summarizes the current status of MRI applications with respect to speech research as well as our own experience of discovery and re-evaluation of acoustic events emanating from the vocal tract and physiological mechanisms.
    No preview · Article · May 2004 · IEICE Transactions on Information and Systems
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    ABSTRACT: This work proposes an experimental method for direct measurement of transfer functions of acoustic tubes. The method obtains a pressure-to-velocity transfer function from measurement of input volume velocity and output pressures of a target tube. Steady sinusoidal waves from 100 Hz to 5 kHz with a 10-Hz increment were used as a source signal. Experimental results compared with transmission line simu- lations indicate the following: (1) transfer functions obtained from the measurements agree well with those from transmis- sion line simulations; (2) differences between the resonant frequenciesobtained fromthe measurementsand simulations with a uniform tube are less than 2.6 %. These results show conclusive evidence that the proposed method permits accu- rate measurements of transfer functions of acoustic tubes.
    Preview · Conference Paper · Jan 2004