中川 誠司

Open and partially closed fractures can trap seismic waves. Waves propagating primarily within fluid in a fracture are sometimes called Krauklis waves, which are strongly dispersive at low frequencies. The behavior of Krauklis waves has previously been examined for an open, fluid-filled channel (fracture), but the impact of finite fracture compliance resulting from contacting asperities and porous fillings in the fracture (e.g., debris, proppants) has not been fully investigated. In this paper, a dispersion equation is derived for Krauklis wave propagation in a fracture with finite fracture compliance, using a modified linear-slip-interface model (seismic displacement-discontinuity model). The resulting equation is formally identical to the dispersion equation for the symmetric fracture interface wave, another type of guided wave along a fracture. The low-frequency solutions of the newly derived dispersion equations are in good agreement with the exact solutions available for an open fracture. The primary effect of finite fracture compliance on Krauklis wave propagation is to increase wave velocity and attenuation at low frequencies. These effects can be used to monitor changes in the mechanical properties of a fracture.

Speech-modulated bone-conducted ultrasound (BCU) can transmit speech sounds for some profoundly deaf individuals. Hearing aids using BCU are considered to be a novel hearing system for such individuals. In our previous study, the speech discrimination for speech-modulated BCU was objectively confirmed using a magnetoencephalography. Moreover, in our previous behavioral study, prosodic information for speech-modulated BCU could also be discriminated in the normal hearing. However, the prosodic discrimination for speech-modulated BCU has not objectively been studied. In order to evaluate the prosodic discrimination for speech-modulated BCU, mismatch fields (MMFs) elicited by prosodic and segmental change were measured for speech-modulated BCU and air-conducted speech. Ten Japanese participants with normal hearing took part in this study. Stimuli re-synthesized from the speech of a native Japanese female adult were used. Standard stimulus was /itta/ with a flat pitch pattern, and two deviant stimuli were /itta?/ with a rising pitch pattern and /itte/ with a flat pitch pattern. All and nine participants elicited the prominent MMF elicited by the prosodic and segmental change for the speech-modulated BCU, respectively. The moment of MMF components for speech-modulated BCU was significantly smaller than those for air-conducted speech, while no difference in the MMF latency elicited by the prosodic and segmental change were observed between both stimulus conditions. Comparing the MMFs elicited by prosodic and segmental change, no significant differences were observed for both stimulus conditions. Thus, it is suggested that the prosodic change can be discriminate to the same degree as segmental change even for speech-modulated BCU. However, discrimination capability for speech-modulated BCU is slightly inferior to that for air-conducted speech. (C) 2013 Elsevier Ireland Ltd. All rights reserved.

When two tones are presented in a short interval of time, the presentation of the preceding tone (masker) suppresses the response evoked by the subsequent tone (signal). To address the processing in forward suppression, we applied 2- and 4-kHz maskers, followed by a 1-kHz signal at varying signal delays (0 to 320 ms) and measured the signal-evoked N1m. A two-way analysis of variance revealed a statistically significant effect for signal delay in both masker presentation conditions. The N1m peak amplitude at the signal delay of 320 ms was significantly larger than those of 10, 20, 40, and 80 ms (p < 0.05). No significant enhancement for the very short signal delay was observed. The results suggest that the enhancement of N1m peak amplitude for short signal delay conditions is maximized when the frequency of the masker is identical to that of the signal.

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf. A novel hearing aid using the perception of amplitude-modulated BCU (BCU hearing aid: BCUHA) has been developed. However, there is room for improvement particularly in terms of sound quality. BCU speech is accompanied by a strong high-pitched tone and contain some distortion. In this study, the sound quality of BCU speech with several types of amplitude modulation [double-sideband with transmitted carrier (DSB-TC), double-sideband with suppressed carrier (DSB-SC), and transposed modulations] and air-conducted (AC) speech was quantitatively evaluated using semantic differential and factor analysis. The results showed that all the types of BCU speech had higher metallic and lower esthetic factor scores than AC speech. On the other hand, transposed speech was closer than the other types of BCU speech to AC speech generally; the transposed speech showed a higher powerfulness factor score than the other types of BCU speech and a higher esthetic factor score than DSB-SC speech. These results provide useful information for further development of the BCUHA. (c) 2013 The Japan Society of Applied Physics

When two tones are presented in a short time interval, the response to the second tone is suppressed. This phenomenon is referred to as forward suppression. To address the effect of the masker laterality on forward suppression, magnetoencephalographic responses were investigated for eight subjects with normal hearing when the preceding maskers were presented ipsilaterally, contralaterally, and binaurally. We employed three masker intensity conditions: the ipsilateral-strong, left-right-balanced, and contralateral-strong conditions. Regarding the responses to the maskers without signal, the N1m amplitude evoked by the left and binaural maskers was significantly larger than that evoked by the right masker for the left-strong and left-right-balanced conditions. No significant difference was observed for the right-strong condition. Regarding the subsequent N1m amplitudes, they were attenuated by the presence of the left, binaural, and right maskers for all conditions. For the left-and right-strong conditions, the subsequent N1m amplitude in the presence of the left masker was smaller than those of the binaural and right maskers. No difference was observed between the binaural and right masker presentation. For left-right-balanced condition, the subsequent N1m amplitude decreased in the presence of the right, binaural, and left maskers in that order. If the preceding activity reflected the ability to suppress the subsequent activity, the forward suppression by the left masker would be superior to that by the right masker for the left-strong and left-right-balanced conditions. Furthermore, the forward suppression by the binaural masker would be expected to be superior to that by the left masker owing to additional afferent activity from the right ear. Thus, the current results suggest that the forward suppression by ipsilateral maskers is superior to that by contralateral maskers although both maskers evoked the N1m amplitudes to the same degree. Additional masker at the contralateral ear can attenuate the forward suppression by the ipsilateral masker.

Human listeners can perceive speech signals in a voice modulated ultrasonic carrier from a bone-conduction stimulator, even if the listeners are patients with sensorineural hearing loss. Considering this fact, we have developed a bone-conducted ultrasonic hearing aid (BCUHA). The purpose of this study was to assess the usefulness of the BCUHA in transmission of the emotional state of the speaker. The evaluation used emotion identification experiments. Types of emotion included Ekman's basic 6 emotions ("anger," "disgust," "fear," "joy," "sadness," and "surprise") and "neutral." The experiments were also conducted under air-conduction (AC) and cochlear implant simulator (CIsim) conditions. The results showed that emotion was transmitted more effectively with the BCUHA than CIsim.

This study aimed to assess the effects of light wavelength on human cortical activity during a cognitive task, by observing event-related potentials (ERPs). We measured ERPs when subjects perform an auditory oddball task under daytime exposures to short-and middle-wavelength lights. In the oddball task, a standard tone of 1 kHz and a target tone of 2 kHz were used. Subjects were instructed to press a button as soon as they heard the target tone. The ERP component that occurs approximately 300 ms after a stimulus onset (P300) was analyzed. The results showed that amplitude of P300 in the short-wavelength light condition was significantly larger than that in the middle-wavelength light condition approximately 1020 min after the start of light exposure. It has been suggested that the amplitude of P300 reflects the amount of attentional resources for a given task. Therefore, the results obtained suggest that amount of attentional resource allocated to the oddball task is increased during exposure to the short-wavelength light in the daytime.

Ultrasonic hearing through bone-conduction is referred to as bone-conducted ultrasound (BCU). Because the perceptual mechanisms of ultrasonic hearing are still unclear, it is necessary to approach the subject from various aspects to clarify such mechanisms; the propagation process of ultrasonic vibration in the head is one of them.To estimate propagation pathways and modes of BCU in living human head, we measured the transient acceleration responses for ultrasonic pulses. The acceleration responses were obtained at the left and right ears simultaneously for left-side, right-side and forehead excitations. Transient responses show that there are several transmission pathways or modes, and the dominant pathways of BCU were identified.

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf. A novel hearing aid using the perception of amplitude-modulated BCU (BCU hearing aid: BCUHA) has been developed. However, there is room for improvement particularly in terms of articulation and sound quality. BCU speech is accompanied by a strong high-pitched tone and contain some distortion. In this study, transposed modulation, that can be expected to reduce the high-pitched tone was newly employed as a modulation method in the BCUHA, and its resulting articulation, intelligibility and sound quality were evaluated. The results showed that transposed modulation showed nearly equal articulation and intelligibility scores to and better sound quality than the existing method, DSB-TC modulation. These results provide useful information for further development of the BCUHA.

Perceptual degree of consonance or dissonance of a chord is known to be varied as a function of frequency ratio between tones composing the chord. It has been indicated that generation of a sense of dissonance is associated with the auditory steady-state response (ASSR) phase-locked to difference frequencies which are salient in the chords with complex frequency ratios. This study further investigated how the neuromagnetic ASSR would be modulated as a function of the frequency ratio when the acoustic properties of the difference frequency, to which the ASSR was synchronized, was identical in terms of its number, energy and frequency. Neuronal frequency characteristics intrinsic to the ASSR were compensated by utilizing responses to a SAM (Sinusoidally Amplitude Modulated) chirp tone sweeping through the corresponding frequency range. The results showed that ASSR was significantly smaller for the chords with simple frequency ratios than for those with complex frequency ratios. It indicates that the basic neuronal correlates underlying the sensation of consonance/dissonance might be associated with the attenuation rate applied to encode the input information through the afferent auditory pathway. Attentional gating of the thalamo-cortical function might also be one of the factors.

Several studies have reported that bone-conducted ultrasounds (BCUs) can be perceived even by those with profound sensorineural deafness, who typically hardly sense sounds even with conventional hearing aids. The perception of BCUs by the profoundly deaf has been objectively proven using magnetoencephalography (MEG). Furthermore, both the psychological characteristics and the neurophysiological mechanisms underlying the perception of BCUs have been identified by psychophysical, electrophysiological and physical approaches. In addition, we have developed a BCU hearing aid (BCUHA) for the profoundly deaf. Remarkable results have already been achieved with this device, which enabled 42% of the profoundly deaf subjects in the trial to perceive some sort of sound and 17% of them to recognize simple words. These results suggest the feasibility of this device, but additional development and improvements are needed.

In this study, we investigated the propagation velocity of bone-conducted ultrasound (BCU) in a living human head. The propagation velocity was calculated using the pattern of acoustic interference, which was extracted from the distribution of the acceleration responses induced as a function of frequency and inter lateral phase difference of bilaterally presented BCU stimuli. Stepped sine signals from 28 to 32 kHz in 100Hz steps with an interlateral phase difference from -2 pi to 2 pi in pi/8 steps were used as excitation signals. The estimated propagation velocities were approximately 300 m/s. Furthermore, a simple numerical simulation for the bilateral presentation of BCU stimuli using the estimated velocity was conducted. The simulated acoustic interference pattern was similar to the results of the actual measurements, supporting the fact that the acoustical interference of BCU stimuli induced by bilateral presentation can be estimated with this model. (C) 2012 The Japan Society of Applied Physics

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf. A novel hearing aid using the perception of amplitude-modulated BCU (BCU hearing aid: BCUHA) has been developed; however, further improvements are needed, especially in terms of articulation and sound quality. In this study, the intelligibility and sound quality of BCU speech with several types of amplitude modulation [double-sideband with transmitted carrier (DSB-TC), double-sideband with suppressed carrier (DSB-SC), and transposed modulation] were evaluated. The results showed that DSB-TC and transposed speech were more intelligible than DSB-SC speech, and transposed speech was closer than the other types of BCU speech to air-conducted speech in terms of sound quality. These results provide useful information for further development of the BCUHA. (C) 2012 The Japan Society of Applied Physics

Human listeners can perceive speech signals in a voice modulated ultrasonic carrier from a bone-conduction stimulator, even if the listeners are patients with sensorineural hearing loss. Considering this fact, we have been developing a bone-conducted ultrasonic hearing aid (BCUHA). The purpose of this study is to evaluate the usability of the BCUHA regarding perception of Japanese prosodic phonemes, specifically, perception of singleton/geminate consonants, short/long vowels and pitch accent. For this purpose, a series of phoneme discrimination experiments was conducted. The results of the experiments showed that no significant difference between air-conduction and BCUHA conditions was observed. These results indicate that the BCUHA can transmit short/long vowels, single/geminate consonants and pitch accent information as well as segmental information.

We investigated the linearity of bone-conducted ultrasound transmission through a living human head. The frequency response functions and the coherence functions of head vibration at different signal levels were examined. Vibrations in the heads of six subjects were measured using a small accelerometer in the ear canal under bone-conducted tone stimulation from audible high frequencies to ultrasonic frequencies. Stepped sine signals from 10 to 45 kHz in 0.5 kHz steps at two different signal levels were used. The signal levels were set to the levels corresponding to 5 and 10 dB sensation level (SL) at 30 kHz in each subject. The result suggests that the head vibration increases almost linearly across an audible to ultrasonic frequency range and there was no significant difference in nonlinear behavior between the audible and ultrasonic sound transmissions. (C) 2011 The Japan Society of Applied Physics

Bone-conducted ultrasound (BCU) modulated by speech sound is recognized as speech sound and activates the auditory cortex similar to audible sound. To investigate the mechanisms of perception, the effects of stimulus duration on N1m were compared among air-conducted audible speech sound (AC speech), AC speech with carrier BCU and speech-modulated BCU in eight native Japanese with normal hearing. The Japanese vowel sound /a/ was used as a stimulus with durations of 10, 15, 20, 30, 40 and 60 ms. Comparison between AC speech with and without carrier showed that the presentation of carrier had no effect on N1m evoked by AC speech. Comparison among the three conditions showed that N1m amplitude for speech-modulated BCU differed from that for the two AC speeches. Moreover, N1m amplitude growth saturated at 40 ms for speech-modulated BCU, and at 20 ms for two AC speeches. These results suggest a difference in temporal integration of N1m between speech-modulated BCU and AC speech. Considering these results, it is reasonable to conclude that N1m evoked by speech-modulated BCU is influenced mainly by the ultrasonic component rather than demodulated audible sound. Given this finding, the notion needs to be considered that the mechanisms underlying perception and recognition of speech-modulated BCU depend on the ultrasonic component to some extent. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

Sediments undergoing compaction typically exhibit transversely isotropic (TI) elastic properties. We present a new experimental apparatus, the phased array compaction cell, for measuring the TI elastic properties of clay-rich sediments during compaction. This apparatus uses matched sets of P- and S-wave ultrasonic transducers located along the sides of the sample and an ultrasonic P-wave phased array source, together with a miniature P-wave receiver on the top and bottom ends of the sample. The phased array measurements are used to form plane P-waves that provide estimates of the phase velocities over a range of angles. From these measurements, the five TI elastic constants can be recovered as the sediment is compacted, without the need for sample unloading, recoring, or reorienting. This paper provides descriptions of the apparatus, the data processing, and an application demonstrating recovery of the evolving TI properties of a compacting marine sediment sample.

Mechanical properties (seismic velocities and attenuation) of geological materials are often frequency dependent, which necessitates measurements of the properties at frequencies relevant to a problem at hand. Conventional acoustic resonant bar tests allow measuring seismic properties of rocks and sediments at sonic frequencies (several kilohertz) that are close to the frequencies employed for geophysical exploration of oil and gas resources. However, the tests require a long, slender sample, which is often difficult to obtain from the deep subsurface or from weak and fractured geological formations. In this paper, an alternative measurement technique to conventional resonant bar tests is presented. This technique uses only a small, jacketed rock or sediment core sample mediating a pair of long, metal extension bars with attached seismic source and receiver-the same geometry as the split Hopkinson pressure bar test for large-strain, dynamic impact experiments. Because of the length and mass added to the sample, the resonance frequency of the entire system can be lowered significantly, compared to the sample alone. The experiment can be conducted under elevated confining pressures up to tens of MPa and temperatures above 100 degrees C, and concurrently with x-ray CT imaging. The described split Hopkinson resonant bar test is applied in two steps. First, extension and torsion-mode resonance frequencies and attenuation of the entire system are measured. Next, numerical inversions for the complex Young's and shear moduli of the sample are performed. One particularly important step is the correction of the inverted Young's moduli for the effect of sample-rod interfaces. Examples of the application are given for homogeneous, isotropic polymer samples, and a natural rock sample. (C) 2011 American Institute of Physics. [doi:10.1063/1.3579501]

An existing problem for speech recognition is that the recognition rate tends to decrease because of the noise. Body-conducted speech offers a robust signal extraction method to extract speech signals from noisy environments, particularly because body-conducted speech is a propagated sound and not easily influenced by noise. However, when body-conducted speech is extracted with an accelerator, the typical frequency component of 2 kHz or more decreases in comparison with normal speech. Therefore, much research has been carried out investigating the techniques for improving the sound quality of body-conducted speech. Particularly, conventional methods require normal speech to estimate clear speech. Here, we propose a technique that combines differential acceleration and noise reduction to estimate a clear signal using only body-conducted speech. By comparing spectrogram differences with each method, we found that the Wiener filtering method was suitable for eliminating noise with differential acceleration. Thereafter, improvements in recognition rates were obtained using retrieval signals although the decoder has an acoustic model made by speech parameters. (C) 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

For a flickering light with two or more frequency components, the temporal envelope of the flickering light is perceived, although there is no frequency component at the frequency of the envelope. To address the processing of the temporal envelope, we compared cortical responses to the envelope of amplitude-modulated (AM) flickering lights with responses to sinusoidal flickering lights. We measured magnetoencephalographic (MEG) responses to AM and sinusoidal flickering lights while changing the frequency of the temporal envelope of AM flickering light and the stimulus frequency of sinusoidal flickering light. The result showed that the strength of the MEG response to sinusoidal flickering light increased with stimulus frequency in the low frequency range. This probably resulted from the band-pass filtering in the visual system. However, such an increase in the low frequency range was not observed for the envelope of AM flickering light. The absence of the increase in MEG responses suggests that the envelope of AM flickering light is not subject to band-pass filtering in the visual system. It is therefore possible that the envelope is represented after the band-pass filtering stage. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

Human listeners can perceive speech signals in a voice-modulated ultrasonic carrier from a bone-conduction stimulator, even if the listeners are patients with sensorineural hearing loss. Considering this fact, we have been developing a bone-conducted ultrasonic hearing aid (BCUHA). The purpose of this study is to evaluate the usability of BCUHA regarding transmission of speaker discrimination information. For this purpose, a prototype of speaker discrimination test was developed. The test consists of 120 pairs of 10 words spoken by 10 speakers, and examinee is requested to judge the speakers of each pair are "same" or "different". The usability of BCUHA was assessed by using the speaker discrimination test. The test was also conduced to air-conduction (AC) and cochlear implant simulator (CIsim) condition. The results show that BCUHA can transmit speaker information speaker as well as CIsim.

<jats:p>Ultrasonic vibration generates a sensation of sound via bone-conduction. This phenomenon is called bone-conducted ultrasonic (BCU) hearing. Complex sounds can also be perceived by amplitude-modulating a BCU stimulus (AM-BCU). The influence of the modulation frequency on the sensitivity to detecting amplitude modulation of sinusoidal carriers of 10, 20, and 30 kHz was examined to clarify the characteristics of the perception of amplitude modulation over the sonic or audio-frequency range and the ultrasonic range. In addition, the detection sensitivity for single-sideband modulation for a 20 kHz carrier was measured. Temporal modulation transfer functions (TMTFs) obtained at each carrier frequency suggest that the auditory system has the ability to process timing information in the envelopes of AM-BCUs at lower modulation frequencies, as is the case with audio-frequency sounds. The possible influence of peripheral filtering on the shape of the TMTF at higher frequencies was examined.</jats:p>