中川 誠司

Sound duration conveys phonemic information in some languages. The present study, using magnetoencephalography (MEG), examined whether the hemispheric activation associated with the processing of duration is different between speech and non-speech sounds in subjects whose native language uses duration as a phonemic cue. The magnetic mismatch negativity (MMNm) response was recorded for equal-duration decrements in vowel, sinusoidal, and spectrally rich complex sounds. Although the MMNm responses to duration changes were predominant in the right hemisphere, the distribution of this response for the vowel stimuli was significantly displaced leftward compared with that for the other two types of stimuli. The results suggest that the hemispheric distribution of the MMNm response to duration change depends on the linguistic relevance of the change.

This study investigates the performance of a frequency domain viscoacoustic full wave form nonlinear inversion to obtain high resolution images of velocity and attenuation. An efficient frequency domain implementation is applied that consists of performing a series of single frequency inversions sweeping from low to high frequency. A cascaded inversion was adopted in which the real part of the velocity is first imaged using the phase information, then the quality factor (Q) is imaged using the amplitude information. Tests with synthetic data indicate that our approach yielded better images than the simultaneous determination of the real and imaginary parts of the complex velocity. The method is applied to laboratory data obtained in a water tank with suspended acrylic bars. Broadband 200 kHz data are obtained for a crosshole configuration with a computer-controlled scanning system and piezofilm source and detector. The velocity image produced by the full wave form inversion is compared to a curved ray travel time tomography velocity image, and was observed to possess higher resolution and more precise locations of the acrylic bars. The Q image shows a lower resolution than the velocity image, but recovers the correct Q for acrylic. This method can be applied for geophysical applications targeted to soil, unconsolidated rocks, and marine sediments and also nondestructive evaluation and medical applications. © 2004 Acoustical Society of America.

In the biomagnetic inverse problem, it is important that the optimal method be selected, especially when estimating internal electrical sources for higher functions with poor information about their source profile. In this paper, internal sources of brain magnetic fields associated with short-term memory processes were estimated by: 1) a nonlinear parameter optimization method using a multidipole model and 2) a linear optimization method using an L1 minimum norm estimation (L1-MNE) technique.. Both methods showed almost the same sources: in the inferior part of the occipital lobe, the supramarginal gyrus and the angular gyrus, and the inferior frontal gyrus. These results indicate the reliability and availability of these methods for brain magnetic data associated with higher brain functions.

Cortical areas involved in processing of emotional prosody (EP) in spoken language, such as joy or sadness, have been found in functional magnetic resonance imaging (fMRI) studies bilaterally or dominantly in the right frontal or temporal lobes. In this study, we investigated spatiotemporal patterns of cortical activity related to EP processing using magnetoencephalography (MEG). In this experiment, a joyful face (JF) or a sad face (SF) was displayed after voices which had emotional features of joy (joy prosody: JP) or sadness (sad prosody: SP) were presented. Subjects were requested to judge whether emotional features of the voice and the face were identical or not. MEG signals evoked by emotional voices were measured and significant differences of cortical activities associated with processing of emotional feature were observed between the right and left hemisphere during the latency of 100-150 ms that includes the N1m component. Our study suggests that MEG is a useful method, in addition to fMRI and event-related scalp potentials (ERP) for studying non-invasively EP processing in the human brain.

Elastic wave scattering off a layer containing a single set of vertical periodic fractures is examined using a numerical technique based on the work of Hennion et al. [J. Acoust. Soc. Am. 87, 1861-1870 (1990)]. This technique combines the finite element method and plane wave method to simulate three-dimensional scattering off a two-dimensional fractured layer structure. Each fracture is modeled explicitly, so that the model can simulate both discrete arrivals of scattered waves from individual fractures and multiply scattered waves between the fractures. Using this technique, we examine changes in scattering characteristics of plane elastic waves as a function of wave frequency, angle of incidence, and fracture properties such as fracture stiffness, height, and regular and irregular spacing.

Auditory sensation is affected by a forward masker, and this phenomenon has been demonstrated in a neural adaptation model and a temporal window (integration) model. To study forward masking in the central auditory system, the growth of the N1m amplitude was measured by varying the signal delay. In the adaptation model, the masking increases as the signal delay decreases. However, in our results, the miN1mum N1m amplitude was observed at a signal delay of 40 ms. As the signal delay decreased from 40 ms, the N1m amplitude increased although the masking increased. Our results suggest that the growth of the N1m amplitude largely depends on temporal integration at signal delays below 40 ms.

Electrogustometry is a convenient method to examine taste acuity in clinical situations. Some basic properties of neural activity in the cerebral cortex in response to electrogustatory stimulation were revealed by measuring magnetoencephalography (MEG) signals with a whole-cortex-type system in response to varying intensities of anodal DC currents focally applied to the tongue surface in human subjects. Independent component analysis was used to eliminate stimulus artifacts in MEG signals. Electrogustatory stimulation with intensities of induced electric taste evoked responses bilaterally, mainly in the opercular-insular cortex with a mean onset latency of approximately 350 ms, while subthreshold electrogustatory stimulation induced modest responses in the cortex. Stronger stimulation induced a tingling sensation and elicited large transient responses in both the opercular-insular and somatic sensory cortices. This is the first description of the basic properties of human MEG responses to electrogustatory stimulation.

Bone conduction enables ultrasound to be heard. Although several hypotheses about ultrasonic perception have been presented, the perception mechanism of bone-conducted ultrasound has not yet been established. In this study, to investigate ultrasonic perception, the amount of masking produced by 27-, 30- and 33-kHz bone-conducted ultrasonic maskers for air-conducted high-frequency sounds was measured in the frequency range of 8-18 kHz at 1-kHz intervals. The results showed that the air-conducted signals in the frequency range of 10-14 kHz were strongly masked by the ultrasonic maskers. When the masker intensity increased from 5 to 10 dB SL, the growth of masking was more than 10 dB in the frequency range of 9-15 kHz, and the masking spread strongly to lower frequencies. Furthermore, the dynamic range for bone-conducted ultrasound was clearly narrower than that for air-conducted high-frequency sounds. These results suggest that perception of bone-conducted ultrasound depends on inner hair cell activity induced by ultrasound, even without modulation being present, and does not depend on enhancement by the outer hair cells in the basal turn of the cochlea.

Bone conduction enables ultrasound to be heard. Although several hypotheses about ultrasonic perception have been presented, the perception mechanism of bone-conducted ultrasound has not yet been established. In this study, to investigate ultrasonic perception, the amount of masking produced by 27-, 30- and 33-kHz bone-conducted ultrasonic maskers for air-conducted high-frequency sounds was measured in the frequency range of 8-18 kHz at 1-kHz intervals. The results showed that the air-conducted signals in the frequency range of 10-14 kHz were strongly masked by the ultrasonic maskers. When the masker intensity increased from 5 to 10 dB SL, the growth of masking was more than 10 dB in the frequency range of 9-15 kHz, and the masking spread strongly to lower frequencies. Furthermore, the dynamic range for bone-conducted ultrasound was clearly narrower than that for air-conducted high-frequency sounds. These results suggest that perception of bone-conducted ultrasound depends on inner hair cell activity induced by ultrasound, even without modulation being present, and does not depend on enhancement by the outer hair cells in the basal turn of the cochlea. (C) 2002 Elsevier Science B.V. All rights reserved.

Cortical site processing the information of whole body linear acceleration has not yet been identified. In this study, neuromagnetic responses to visually induced linear forward acceleration were recorded in six healthy-right-handed adult subjects using a 122-channel whole cortex neuromagnetometer. Significant activation was estimated in the cortex around the posterior insula, which belongs to the vestibular cortex. Hence, it is suggested that the vestibular cortex not only receives vestibular input from the peripheral vestibular apparatus, but also processes the vestibular sensation from multi-modal information.

Ultrasound can be heard by bone conduction in man. However, there has been no consensus about the perception mechanism of bone-conducted ultrasound (BCU). In the current study, to clarify the central auditory system of BCU, the effects of stimulus duration for 30 kHz BCU on N1m were compared with those for air-conducted 1 kHz tone bursts by magnetoencephalography. As a result, the growth of N1m amplitude for both stimuli saturated at the duration of 40 ms, which suggest that the temporal integration system of BCU is similar to that of audible sound. However, significant differences in the growth were observed below the saturation points. The results indicate a possibility that there are some differences in the central auditory system between BCU and audible sound.

Ultrasound can be heard by bone conduction in man. However, there has been no consensus about the perception mechanism of bone-conducted ultrasound (BCU). In the current study, to clarify the central auditory system of BCU, the effects of stimulus duration for 30 kHz BCU on N1m were compared with those for air-conducted 1 kHz tone bursts by magnetoencephalography. As a result, the growth of N1 nn amplitude for both stimuli saturated at the duration of 40 ms, which suggest that the temporal integration system of BCU is similar to that of audible sound. However, significant differences in the growth were observed below the saturation points. The results indicate a possibility that there are some differences in the central auditory system between BCU and audible sound. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

The phenomenon physically occurring within the head for bone-conducted sound of various stimulation locations has been calculated using the finite-difference time-domain (FDTD) technique; three slightly different stimulation locations near the left mastoid were set for audible and ultrasonic frequency stimulation. Calculated sound fields at the plane including the cochleae showed considerably different characteristics at different stimulation frequencies. For audible frequency stimulation, their distribution negligibly differed for each stimulation location. On the contrary, for ultrasonic frequency stimulation, their distribution shifted considerably for each different stimulation location. These results indicated the characteristics of the shifting sound image perceived for bone-conducted ultrasound and the negligibly shifting sound image perceived for bone-conducted audible sound, from the slight changes in their stimulation locations.

The phenomenon physically occurring within the head for bone-conducted sound of various stimulation locations has been calculated using the finite-difference time-domain (FDTD) technique; three slightly different stimulation locations near the left mastoid were set for audible and ultrasonic frequency stimulation. Calculated sound fields at the plane including the cochleae showed considerably different characteristics at different stimulation frequencies. For audible frequency stimulation, their distribution negligibly differed for each stimulation location. On the contrary, for ultrasonic frequency stimulation, their distribution shifted considerably for each different stimulation location. These results indicated the characteristics of the shifting sound image perceived for bone-conducted ultrasound and the negligibly shifting sound image perceived for bone-conducted audible sound, from the slight changes in their stimulation locations.

Human cortical responses corresponding to the subjective preference for a flickering light of varying period were investigated. Paired-comparison tests were performed to examine the subjective preference for a flickering light, and MEG was recorded during presentations of the most preferred and less preferred flickering lights alternately. Results showed that the effective duration of the autocorrelation function, tau(e), which represents a repetitive feature of the MEG alpha waves, becomes longer during the preferred condition. This reveals that the brain repeats a similar rhythm under preferred conditions.

The quest to extract rock properties from seismic images has resulted in a growing interest in full waveform inversion and imaging. This study applies frequency-domain visco-acoustic waveform inversion and reverse-time imaging to synthetic and laboratory data. The laboratory data for a crosshole configuration is obtained with a two-axes computer-controlled scanning system. Broadband 200 kHz data is obtained using a piezofilm source and detector in a water tank with suspended acrylic bars. The velocity image produced by the waveform inversion has a higher resolution and more precisely determines the location of the acrylic bars compared to the traveltime tomography image. The Q imaging has poorer resolution and is less reliable than the velocity imaging. The reverse-time imaging of scattered waves can image the bars as well as the water surface.

Ultrasounds are perceived through bone-conduction by profoundly deaf as well as normal hearing subjects. A bone-conducted ultrasonic hearing aid (BCUHA) was developed for the profoundly deaf Parameters of BCUHA were determined by former psychoacoustic and neuromagnetic experiments, Using BCUHA. 53% of the Profoundly deaf subjects were able to perceive sounds. and 18 of them were able to recognize some words.

骨導で呈示された超音波(以下, 骨導超音波と呼ぶ)の聴覚心理学的特徴や知覚中枢部位などについてはこれまでに明らかにされてきたが, 末梢における聴覚系の関与などについては, いまだ不明な点が多く残されている.そこで本論文では, 頭部モデルを用いた実測及び数値シミュレーションを行い, 骨導音呈示時に生体中に形成される音場の計算結果などから, 骨導超音波知覚の末梢における関与について検討した.その結果, 刺激周波数が可聴域のときと超音波領域のときとで蝸牛付近に形成される音場に明らかな違いが見られた.また, 知覚音の聴覚心理学的特徴との関連も見られた.この結果は, 骨導超音波によって実現されると考えられている.重度の難聴者に対する補聴システムの開発に有効な設計指針を与えるものである.

The aim of this study is to identify the relationship between subjective preference and the human brain responses to visual motion under changing its period. First, preference judgments using the paired-comparison method for sinusoidal movements of a single circular target in horizontal direction were performed. Then, MEG data were recorded during presentations of the most preferred and the least preferred moving stimuli. From the initial delay range of ACF of the alpha wave, the effective duration (tau(c)) was analyzed. Results show that the stimulus with most preferred periods has a greater value of tau(c) than that with least preferred periods at the occipital area, especially in the left hemisphere.

The cortical site which processes information on whole-body linear displacement is unknown. In this study, neuromagnetic responses to a visually-induced linear vection were recorded in 5 healthy, right-handed, adult subjects using a 122-channel whole cortex neuromagnetometer. We presented expanding rectangles on the screen which came into view one after another and accelerated in expanding speed at random cycle, giving the subjects the sensation of linear self motion (linear vection) through an illusory tunnel with occasional acceleration. Clear responses of magnetic fields related to the accelerative event were obtained in both hemispheres around the parietal and temporal regions. The dipole sources of the component were estimated in the cortex around the superior temporal sulcus, insula and medial superior temporal area. Some parts of these regions may have been comprised in the vestibular cortex, suggesting that it processes the sensation of linear self motion and plays an important role in space perception.

The aim of this study is to identify the relationship between subjective preference and the human brain responses to visual motion under changing its period. First, preference judgments using the paired-comparison method for sinusoidal movements of a single circular target in horizontal direction were performed. Then, MEG data were recorded during presentations of the most preferred and the least preferred moving stimuli. From the initial delay range of ACF of the alpha wave, the effective duration (τe) was analyzed. Results show that the stimulus with most preferred periods has a greater value of τe than that with least preferred periods at the occipital area, especially in the left hemisphere.

The cortical site which processes information on whole-body linear displacement is unknown. In this study, neuromagnetic responses to a visually-induced linear vection were recorded in 5 healthy, right-handed, adult subjects using a 122-channel whole cortex neuromagnetometer. We presented expanding rectangles on the screen which came into view one after another and accelerated in expanding speed at random cycle, giving the subjects the sensation of linear self motion (linear vection) through an illusory tunnel with occasional acceleration. Clear responses of magnetic fields related to the accelerative event were obtained in both hemispheres around the parietal and temporal regions. The dipole sources of the component were estimated in the cortex around the superior temporal sulcus, insula and medial superior temporal area. Some parts of these regions may have been comprised in the vestibular cortex, suggesting that it processes the sensation of linear self motion and plays an important role in space perception.