中川 誠司

Shales display significant seismic anisotropy that is attributed in part to preferred orientation of constituent minerals. This orientation pattern has been difficult to quantify because of the poor crystallinity and small grain size of clay minerals. A new method is introduced that uses high-energy synchrotron X-rays to obtain diffraction images in transmission geometry and applies it to an illite-rich shale. The images are analyzed with the crystallographic Rietveld method to obtain quantitative information about phase proportions, crystal structure, grain size, and preferred orientation (texture) that is the focus of the study. Textures for illite are extremely strong, with a maximum of 10 multiples of a random distribution for (001) pole figures. From the three-dimensional orientation distribution of crystallites, and single-crystal elastic properties, the intrinsic anisotropic elastic constants of the illite aggregate (excluding contribution from aligned micropores) can be calculated by appropriate medium averaging. The illitic shale displays roughly transverse isotropy with C-11 close to C-22 and more than twice as strong as C-33. This method will lend itself to investigate complex polymineralic shales and quantify the contribution of preferred orientation to macroscopic anisotropy.

Red berries of a tropical plant called miracle fruit, Richadella dulcijlca, reduce the sour and aversive taste of acids and add sweet and palatable taste. To elucidate the brain mechanism of this unique action of miracle fruit, we recorded taste-elicited magnetic fields of the human cerebral cortex. The initial taste responses were localized in the fronto-parietal opercular/insular cortex reported as the primary taste area. The mean latency of the response to citric acid after chewing miracle fruit was essentially the same as that for sucrose and was 250-300 ms longer than that for citric acid. Since it is known that stimulation with acids after the action of miracle fruit induces both sweetness and sourness responses in the primate taste nerves, the present results suggest that the sourness component of citric acid is greatly diminished at the level of subcortical relays, and mostly sweetness information reaches the cortical primary taste area. We propose the idea that the qualitative aspect of taste is processed in the primary taste area and the affective aspect is represented by the pattern of activation among the different cortical areas. (c) 2006 Elsevier Inc. All rights reserved.

Psychophysical experiments in humans have indicated that the auditory system has a well-defined bandwidth for resolution of complex stimuli. This bandwidth is known as the critical bandwidth (CBW). Physiological correlates of the CBW were examined in the human auditory cortex. Two- and three-tone complexes were used as the sound stimuli with all signals presented at 55 dB sound pressure level (SPL). The duration of stimulation was 500 ins, with rise and fall ramps of 10 ins. Tell normal-hearing subjects took part in the study. Auditory-evoked fields were recorded using a 122-channel whole-head magnetometer in a magnetically shielded room. The latencies, source strengths, and coordinates of the N1m waves, which were found above the left and right temporal lobes approximately 100 ms after the onset of stimulation, were analyzed. The results indicated that NI in amplitudes were approximately constant when the frequency separation of a two-tone complex or the total bandwidth of a three-tone complex was less than the CBW; however, the N1m amplitudes increased with increasing frequency separation or total bandwidth when these were greater than the CBW. These findings indicate critical band-like behavior in the human auditory cortex. The NI in amplitudes in the right hemisphere were significantly greater than those in the left hemisphere, which may reflect a right-hemispheric dominance in the processing of tonal Stimuli. (c) 2006 Elsevier B.V. All rights reserved.

<jats:p>Several studies have reported that bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf; however, the mechanisms involved remain unclear. We previously reported some unique characteristics of BCU perception: (1) the pitch of BCU is about ten-odd kHz and is independent of its frequency, (2) the dynamic range of BCU is narrow, less than 20 dB, and (3) BCU mask 10–15-kHz air-conducted sounds. In this study, cortical magnetic field (N1m), middle latency (MLRs) and auditory brainstem responses (ABRs) and electrocochleogram (EcochG) evoked by BCU in human were recorded to clarify the neural pathway for BCU. Substantial MLRs and ABRs (wave-I–V) were evoked by BCU as well as by air-conducted sound. Although a clear N1m response was elicited by BCU and its equivalent current dipoles (ECDs) were estimated in the auditory cortices, ECD locations for BCU did not follow the tonotopic organization at the cortical level. Both wave I of ABRs and AP of EcochG were observed clearly, indicating that the auditory nerve was substantially activated. These results suggest that BCU goes through the normal auditory pathway—there are no special organs for BCU perception; however, unique processes may exist in the cochlea.</jats:p>

The detection of interaural time differences (ITD) for sound localization depends on the similarity between the left and right ear signals, namely interaural correlation (IAC). Human localization performance deteriorates with decreasing IACs. In order to examine activity related to localization performance in the human cortex, auditory evoked magnetic fields to the ITD of bandpass noises with different IACs were analyzed. When the JAC was 0.95, the N1m, amplitudes, i.e., the estimated equivalent current dipole moments, increased with increasing ITD. However the effect of ITD on the N1m amplitudes was not significant when the IAC was 0.5. When the ITD was 0.7 ins, the N1m amplitudes decreased with decreasing IACs. There were no systematic changes in the source location of N1m in the auditory cortex related to changes in ITD or IAC. The results suggest that localization performance is reflected in N1m amplitudes. (c) 2006 Elsevier B.V. All rights reserved.

This paper describes the relationship between the eigenfrequencies of CT scanned realistic human head model and the subjective detecting pitch, which is given by providing the bone-conducted ultrasound. Our goal is to develop the optimal bone-conducted ultrasonic hearing aid for profoundly hearing-impaired persons. An ascent of a speech intelligibility is the requirement of hearing aid. To improve it, the perception mechanism of the bone-conducted ultrasound must be clarified, but the conclusive agreement of it has not been reached yet, although many hypotheses were reported.The authors feel an interest in the detecting pitch of bone-conducted ultrasound with no frequency-dependence and predict that the cochleae are related to the perception mechanism for bone-conducted ultrasound, since it has been verified that the auditory cortex responds to bone-conducted ultrasound by MEG study.In this paper, waves propagating from the mastoid to both cochleae are numerically analyzed and the characteristics of transfer functions are estimated as a first step to clarifying the perception mechanism for detecting pitch of bone-conducted ultrasonic stimuli.

Auditory evoked magnetic fields in relation to the center frequency of sound with a certain bandwidth were examined by magnetoencephalography (MEG). Octave band, 1/3 octave band, and 130 Hz bandwidth noises were used as the sound stimuli. All signals were presented at 60 dB SPL. The stimulus duration was 500 ms, with rise and fall ramps of 10 ms. Ten normal-hearing subjects took part in the study. Auditory evoked fields were recorded using a 122 channel whole-head magnetometer in a magnetically shielded room. The latencies, source strengths and coordinates of the N1m wave, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, were analyzed. The results demonstrated that the middle frequency range had shorter N1m latencies and larger N1m amplitudes, and that the lower and higher frequency stimuli had relatively delayed N1m latencies and decreased N1m amplitudes. The N1m amplitudes correlated well to the loudness values in the frequency ranges between 250 and 2000 Hz. The source locations of N1m did not reveal any systematic changes related to the center frequency and bandwidth. (c) 2006 Elsevier B.V. All rights reserved.

Bone-conducted ultrasounds (BCUs) can be perceived by the profoundly deaf, who hardly sense sounds even with conventional hearing aids, as well as normal-hearing subjects. A bone-conducted ultrasonic hearing aid (BCUHA) was developed for the profoundly deaf. With the BCUHA, ultrasounds at about 30 kHz are amplitude-modulated by speech sounds and presented to the user's mastoid by a vibrator, and users can perceive demodulated speech sounds. The basic parameters of the BCUHA were determined from the results of our former studies of the characteristics of BCU perception. Psychoacoustical tests were carried out to evaluate the utility of the BCUHA. The results showed: (1) more than 40% of profoundly deaf subjects were able to perceive sounds and 17% were able to recognize words using BCUHA; (2) articulations for Japanese monosyllables were about 60%; and, (3) intelligibility for familiar 4-mora Japanese words reached 80%. These results indicate the practicability of BCUHA.

Bone-conducted ultrasounds (BCUs) can be perceived by the profoundly deaf, who hardly sense sounds even with conventional hearing aids, as well as normal-hearing subjects. A bone-conducted ultrasonic hearing aid (BCUHA) was developed for the profoundly deaf. With the BCUHA, ultrasounds at about 30kHz are amplitude-modulated by speech sounds and presented to the user&#039;s mastoid by a vibrator, and users can perceive demodulated speech sounds. The basic parameters of the BCUHA were determined from the results of our former studies of the characteristics of ECU perception. Psychoacoustical tests...

Modeling the effect of seismic stimulation employing Maxwell-Boltzmann theory shows that the important component of stimulation is mechanical rather than fluid pressure effects. Modeling using Biot theory (two phases) shows that the pressure effects diffuse too quickly to be of practical significance. Field data from actual stimulation will be shown to compare to theory

Changes in the bandwidth affect the perceived loudness of a stimulus even when the level of the stimulus remains fixed. If the bandwidth of a sound is varied while maintaining the overall intensity, the loudness remains constant as long as the bandwidth is less than the critical bandwidth. If the bandwidth is increased beyond the critical bandwidth, the loudness increases with increasing bandwidth. Human cortical responses as a function of stimulus bandwidth were examined by recording auditory-evoked magnetic fields. The results showed that the N1m magnitudes, that is, the estimated equivalent current dipole moments, increased with increasing bandwidth when the bandwidth was increased beyond the critical bandwidth.

Ultrasound can be perceived through bone conduction by the profoundly deaf as well as by normal-hearing subjects. Moreover, speech signals modulated onto ultrasound can be detected through bone conduction. This study explored how well listeners can understand ultrasonic speech and the confusion patterns to evaluate and improve bone-conducted ultrasonic hearing. The intelligibility of Japanese words classified by familiarity and Japanese monosyllables with bone-conducted ultrasound was investigated. Results showed that the intelligibility of familiar words was higher than that of unfamiliar words. Further, the results of a monosyllable intelligibility test with bone-conducted ultrasound and those of a test with air-conducted sound showed a similar pattern of speech recognition with regard to the errors made. The relationship between speech intelligibility and sound level showed that the increase in the intelligibility of bone-conducted ultrasonic speech did not exceed the increase in the intelligibility of air-conducted speech as the sound level rose.

Auditory motion can be simulated by presenting binaural sounds with time-varying interaural time delays. Human cortical responses to the rate of auditory motion were studied by recording auditory evoked magnetic fields with a 122-channel whole-head magnetometer. Auditory motion from central to right and then to central was produced by varying interaural time differences between ears. The results showed that the N1m latencies and amplitudes were not affected by the fluctuation of interaural time delay; however, the peak amplitude of P2m significantly increased as a function of fluctuation of the interaural time delay.

Auditory evoked magnetic fields in relation to iterated rippled noise (IRN) were examined by magnetoencephalography (MEG). IRN was used as the sound stimulus to control the peak amplitude of the autocorrelation function of the sound. The IRN was produced by a delay-and-add algorithm applied to bandpass noise that was filtered using fourth-order Butterworth filters between 400-2200 Hz. All sound signals had the same sound pressure level. The stimulus duration was 0.5 s, with rise and fall ramps of 10 ms. Ten normal-hearing subjects took part in the study. Auditory evoked fields were recorded using a 122 channel whole-head magnetometer in a magnetically shielded room. The results showed that the peak amplitude of N1m, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, increased with increase in the number of iterations of the IRN. The latency and estimated equivalent current dipole (ECD) locations of N1m did not show any systematic variation as a function of the number of iterations.

Human listeners can perceive speech from a voice-modulated ultrasonic carrier presented via a bone-conduction stimulator. This study explored the psychoacoustic characteristics and underlying mechanisms of ultrasonic hearing by measuring difference limens for frequency (DLF) for pure tones modulated onto ultrasonic carriers. Human subjects were presented with two pulsed tones and asked to judge whether the first or the second had the higher pitch. When amplitude modulation was based on a double side-band transmitted carrier, the DLFs were as small as those from the air-conducted pure tones at 0.25-4 kHz. Ultrasounds yielded larger DLFs for tones with low (0.125 kHz) and high (6-8 kHz) frequencies. Results were essentially identical between the two types of carriers, sine wave (30 kHz) and bandpass noise (30+/-4 kHz), despite the different bandwidths in the ultrasonic range. When amplitude modulation was based on a double side-band suppressed carrier, DLFs corresponded to those from tones with double frequencies. These results suggest nonlinear conduction that demodulates audible signals from ultrasounds and provides inputs to the cochlea.

The simplest and most widely used method in the biomagnetic inverse problem is the nonlinear parameter estimation using single-dipole model. However, when the number of activated brain areas is more than one, this simplest dipole solution leads to estimation errors. We evaluated the errors of position, strength, and orientation of the sources estimated by using this single-dipole method when applied to twin-dipole activity using locally-selected channels rather than all channels of the whole-head measurement system. The results suggest the errors generated by the single-dipole method using locally selected channels may be acceptable in some conditions, such as estimating activities of both auditory cortices.

Auditory evoked magnetic fields in relation to the bandwidth of bandpass noise were examined by magnetoencephalography (MEG). Pure tone and bandpass noises with center frequencies of 500, 1000 or 2000 Hz were used as the auditory signals. All source signals had the sound pressure level set at 74 dB. The stimulus duration was 0.5 s, with rise and fall ramps of 10 ms. Eight volunteers with normal hearing took part in the study. Auditory evoked fields were recorded using a neuromagnetometer in a magnetically-shielded room. The results showed that the peak amplitude of N1m, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, decreased with increasing bandwidth of the bandpass noise. The latency and estimated equivalent current dipole (ECD) locations of N1m did not show any systematic variation as a function of the bandwidth for any of the center frequencies.

The cortical areas involved in processing of emotional prosody (EP), such as joy or sadness, have been reported to be localized in the right basal ganglia, frontal lobes or bilateral temporal lobes in recent fMRI studies. Moreover, event-related brain potentials have not been shown to have ERP components with latencies associated with EP recognition, namely N1, P2 and P3. So, we investigated a processing of EP using magnetoencephalograpby (MEG), which has a high time and space resolution. In the test session, an emotional voice (expressing joy, sadness or normal mood, and calling a name consisting of 5 moras) was presented, followed by a 900 ins interstimulus interval and then an emotional face (the same emotion as the voice) was displayed for 1000 ms. The subjects were requested to judge whether or not the emotional features of the voice and face were identical. In the control session, the emotional voices were presented while the subjects carried out visual working memory (n-back) tasks between two sessions, and significant differences in the cortical activities associated with processing of EP were observed during the latencies in different periods after the onset of stimuli in both hemispheres. (c) 2004 Elsevier B.V. All rights reserved.

Recent studies of sound localization in the horizontal plane have revealed that the right hemisphere is dominant in auditory spatial processing of sounds from different directions. In this study, human cortical activity in response to sound sources located in the median plane was investigated. Auditory stimuli, broad-band noises (100-10,000 Hz), were modified by convolutions with head-related transfer functions (HRTFs) to allow the perception of sound sources outside the head, and were virtually presented from different directions in the median plane. The stimuli were delivered to the ears of subjects using plastic tubes to avoid magnetic interference. Auditory evoked magnetic fields were recorded using a 122-channel whole-head SQUID magnetometer in a magnetically shielded room. Two experiments were conducted with stimuli convolved/unconvolved with HRTFs. Magnetoencephalography (MEG) data obtained from the temporal areas of the left and right hemispheres were chosen and the largest amplitudes of major activity peaks elicited by the auditory stimuli were analyzed. The results showed that the right hemisphere tended to be more sensitive in processing sound sources located in the median plane. (c) 2004 Elsevier B.V. All rights reserved.

This study investigated the effect of word familiarity of visual stimuli on the word recognizing function of a human brain. Word familiarity is an index of the relative ease of word perception, and is characterized by facilitation and accuracy on word recognition. We studied the effect of word familiarity, using "Hiragana" (phonetic characters in Japanese orthography) characters as visual stimuli, on the elicitation of visually evoked magnetic fields with a word-naming task. The words were selected from a database of lexical properties of Japanese. The four "Hiragana" characters used were grouped and presented in four classes of degree of familiarity. The three components were observed in averaged waveforms of the root mean square (RMS) value on latencies at about 100, 150 and 220 ins. The RMS value of the 220 ms component showed a significant positive correlation (F=(3/36); 5.501; p=0,035) with the value of familiarity. ECDs of the 220 ms component were observed in the intraparietal sulcus (IPS). Increments in the RMS value of the 220 ms component, which might reflect ideographical word recognition, retrieving "as a whole" were enhanced with increments of the value of familiarity. The interaction of characters, which increased with the value of familiarity, might function "as a large symbol"; and enhance a "pop-out" function with an escaping character inhibiting other characters and enhancing the segmentation of the character (as a figure) from the ground. (c) 2004 Published by Elsevier B.V.

The relation between human brain responses to an individual's annoyance of bandpass noise was investigated using magnetoencephalography (MEG) measurements and analysis by autocorrelation function (ACF) and cross-correlation function (CCF). Pure tone and bandpass noises with a centre frequency of 1000 Hz were used as source signals. The sound pressure level was constant at 74 dBA and the duration of the stimulus was 2.0 s. The scale values of annoyance for each subject were obtained by paired-comparison tests. In MEG measurements, the combination of a reference stimulus (pure tone) and test stimuli (bandpass noise) was alternately presented 30 times at a constant 2 s interstimulus interval. The results show that the effective duration of the ACF, T, of MEG in the 8-13 Hz range, which represent repetitive features within the signal itself, became shorter during the presentation of an annoying stimulus. Also, the maximum value of the CCF, \phi(t)\(max), became smaller. The shorter t(e), and smaller \phi(t)\(max) indicate that a wider area of the brain is unstable for longer with annoying auditory stimuli. (C) 2004 Elsevier Ltd. All rights reserved.

Auditory evoked magnetic fields of the human brain were analyzed in relation to the magnitude of the inter-aural cross-correlation (IACC). IACC of the stimuli was controlled by mixing diotic bandpass and dichotic independent bandpass noise in appropriate ratios. The auditory stimuli were binaurally delivered through plastic tubes and earpieces inserted into ear canals of the nine volunteers with normal hearing who took part in this study. All source signals had the same sound pressure level. Auditory evoked fields (AEFs) were recorded using a neuromagnetometer in a magnetically shielded room. Combinations of a reference stimulus (IACC=1.0) and test stimuli (IACC=0.2, 0.6, 0.85) were presented alternately at a constant interstimulus interval of 0.5 s and MEGs recorded. The results showed that the N1m latencies were not affected by IACC; however, the peak amplitude of N1m significantly decreased with increasing IACC.

The effect of frequency on N1m has been investigated by various methods. However, it has not yet been measured using forward masking. In this study, the frequency specificity of N1m was investigated using forward masking. Although the masker frequency had some influence on N1m amplitudes, the results suggested that the frequency specificity of N1m was worse than that of a single-neuron or psychological tuning curve. This is probably because N1m includes various components, both frequency-specific and non-specific, some of which may be less affected by masking. Thus, our results agree with those of previous studies using intervening tones that suggested widespread neural representation in the auditory cortex.

Voice recognition utilizing bone-conducted voice, which is very robust under noisy environment, has been investigated. The suitability for voice recognition and voice communication of bone-conducted voice recorded at several measurement points on human head was evaluated using LPC cepstrum distance (LCD) and Speech Transmission Index (STI). Experimental results show that forehead and cheek are good as the acquisition points of bone-conducted voice. In order to improve the quality of bone-conducted voice, a novel sensor, which has an inclined frequency response, was fabricated. Using the sensor, acquired bone-conducted voice has a similar frequency response as that of air-conducted voice. Spectral Subtraction is suggested as a method to improve the voice recognition ratio of bone-conducted voice.

The effect of frequency on N1m has been investigated by various methods. However, it has not yet been measured using forward masking. In this study, the frequency specificity of N1m was investigated using forward masking. Although the masker frequency had some influence on N1m amplitudes, the results suggested that the frequency specificity of N1m was worse than that of a single-neuron or psychological tuning curve. This is probably because N1m includes various components, both frequency-specific and non-specific, some of which may be less affected by masking. Thus, our results agree with those of previous studies using intervening tones that suggested widespread neural representation in the auditory cortex.

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.