中川 誠司

We have been developing novel mobile phones using bone conduction, with flat-panel loudspeakers that convey speech sound by vibrating the pinna. In bone conduction via the pinna, i.e., pinna conduction, it is thought that speech sounds are conveyed via both air- and bone-conduction pathways. To obtain useful information for further development of bone-conduction mobile phones, peripheral mechanisms of the pinna conduction need to be clarified. In this study, hearing thresholds, sound field in the outer ear canals, and vibrations of the inner wall of the outer ear canals were measured while normal-hearing participants used pinna-conduction mobile phones.Thresholds decreased linearly as contact pressure increased below 1 kHz, but contact pressure did not affect thresholds above 2 kHz. Additionally, sound fields in the ipsilateral ear canal showed similar results. These results indicate that there is a considerable degree of bone-conduction components from the pinna to the inner ear, which only allow sounds below 1 kHz through. Because similar characteristics were observed in the threshold and the sound field in the outer ear canal, we suggest that osseotympanic emission, sound emission into the ear canal from the inner wall, and air conduction via external auditory foramen are the dominant components of pinna conduction.However, in the vibration measurement, differences between the ipsi- and contra-lateral responses were smaller than the sound field measurement. The smaller inter-lateral differences of the vibration in the outer ear canal suggest the existence of a significant amount of bone-conduction components that directly reach the middle or inner ear. Although the amount of such bone-conduction components does not seem sufficient for pinna

Objective: This study aimed to capture the neuronal frequency characteristics, as indexed by the auditory steady-state response (ASSR), relative to physical characteristics of constant sound pressure levels (SPLs). Relationship with perceptual characteristics (loudness model) was also examined.Methods: Neuromagnetic 40-Hz ASSR was recorded in response to sinusoidally amplitude-modulated sweep tones with carrier frequency covering the frequency range of 0.1-12.5 kHz. Sound intensity was equalized at 50-, 60-, and 70-dB SPL with an accuracy of +/- 0.5-dB SPL at the phasic peak of the modulation frequency. Corresponding loudness characteristics were modeled by substituting the detected individual hearing thresholds into a standard formula (ISO226: 2003(E)).Results: The strength of the ASSR component was maximum at 0.5 kHz, and it decreased linearly on logarithmic scale toward lower and higher frequencies. Loudness model was plateaued between 0.5 and 4 kHz.Conclusions: Frequency characteristics of the ASSR were not equivalent to those of SPL and loudness model. Factors other than physical and perceptual frequency characteristics may contribute to characterizing the ASSR.Significance: The results contribute to the discussion of the most efficient signal summation for the generation of the ASSR at 0.5 kHz and efficient neuronal processing at higher frequencies, which require less energy to retain equal perception. (C) 2015 International Federation of Clinical Neurophysiology. Published by 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. Taking this fact into account, we have developed a bone-conducted ultrasonic hearing aid (BCUHA). However, there remains considerable scope for improvement, particularly in terms of sound quality. Voice-modulated BCU is accompanied by a strong high-pitched tone and some distortion depending on the amplitude modulation method. In this study, the sound quality of a BCUHA with double-sideband transmitted carrier (DSB-TC) modulation and double-sideband suppressed carrier (DSB-SC) modulation methods was examined. The assessment was conducted by examining the transmission of the emotional state of the speaker. The evaluation used emotion-identification experiments. Types of emotion included Ekman's basic six emotions (“anger,” “disgust,” “fear,” “joy,” “sadness,” and “surprise”) and “neutral.” In addition, a series of subjective evaluations regarding “voice clarity,” “comfortableness,” and “preference” was conducted. The results showed that although DSB-SC sound was superior in “comfortableness” and “preference,” voice emotion transmission was more effective in DSB-TC conditions.

Birdsong is often used as an auditory signal for visually-challenged people in public spaces in Japan. However, more than 40% of visually-challenged people reported that such auditory signals were difficult to identify. We used auditory evoked magnetic field (AEF) responses in the human auditory cortex to uncover an auditory signal that was easy to identify. As an auditory signal, we focused on birdsong, which is currently used to inform passengers about the location of stairs in train stations in Japan. We presented birdsongs to participants in silent, noisy, reverberated, and interaural time-delay conditions. We analyzed the most prominent AEF response, N1m, and the correlation between the birdsong envelopes and the AEF. We found that the N1m amplitudes were maximal when the participants listened to the song of the Cuckoo and the above-mentioned correlation was maximal when the participants listened to the song of the Oriental Scops Owl. Thus, we believe the songs of the Cuckoo and Oriental Scops Owl to be candidates for optimal auditory signals. (C) 2015 Elsevier Ltd. All rights reserved.

A novel hearing aid system utilizing amplitude-modulated bone-conducted ultrasound (AM-BCU) is being developed for use by profoundly deaf people. However, there is a lack of research on the acoustic aspects of AM-BCU hearing. In this study, acoustic fields in the ear canal under AMBCU stimulation were examined with respect to the self-demodulation effect of amplitude-modulated signal components generated in the ear canal. We found self-demodulated signals with an audible sound pressure level related to the amplitude-modulated signal components of bone-conducted ultrasonic stimulation. In addition, the increases in the self-demodulated signal levels at low frequencies in the ear canal after occluding the ear canal opening, i.e., the positive occlusion effect, indicate the existence of a pathway by which the self-demodulated signals pass through the aural cartilage and soft tissue, and radiate into the ear canal. (C) 2015 The Japan Society of Applied Physics

Here, we propose a color barrier-free illumination consisting of white, red, and blue LEDs for people with deuteranopia-type defects in color perception. Color perceptions of 20 volunteers with normal vision and four examinees of deuteranopia were evaluated by both the Ishihara test for color blindness and the Farnsworth Panel D-15 test under color barrier-free illumination. The illumination was comparably effective, not only for discriminating between red and green but also for discrimination of the hues on a color chip continuously. (c) 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 218-223, 2015

Because body-conducted speech (BCS) sounds are conducted by skin, muscle, and bone and are not easily disrupted by airborne noises, noise-robust methods of speech detection using BCS have been developed. However, the intelligibility of BCS quickly deteriorates because it does not contain high-frequency components greater than 2 kHz. Thus, we previously proposed and evaluated a method that improves the sound quality of BCS using acceleration difference and noise reduction techniques. However, assessments based on human perception are essential. Consequently, in this paper, we report on evaluations conducted to verify the efficacy of the proposed method using word intelligibility tests and subjects with normal hearing.

Exposure to light modulates not only human alertness but also cognitive functions. The present study examined the temporal dynamics of the effects of light exposure on cortical activity related to cognitive processes. Event-related potentials (ERPs) were measured while participants performed an auditory oddball task during exposure to short-, medium- or long-wavelength light or darkness. Experiments were conducted in the daytime. After a 10-min period of darkness, one of the three lights was presented for 28 min. In the control condition, darkness was maintained for the entire session. The ERP component observed approximately 300 ms after the onset of the target stimulus (P300) was analyzed. The amplitude of P300 was larger after 5-20 min of exposure to short-wavelength light than at equivalent time points in the darkness. No differences were observed in the amplitude of P300 between the medium- or long-wavelength light condition and darkness at any time point. These results suggest that the amount of attentional resource allocated to the oddball task was increased by daytime exposure to short-wavelength light, and that following approximately 5 min of exposure the impact of light on cortical activity related to cognitive processes was able to be detected. (C) 2014 Elsevier Inc All rights reserved.

The Krauklis wave is a slow dispersive wave mode that propagates in a fluid layer bounded by elastic media. The guided properties of this wave and its ability to generate very short wavelengths at seismic frequency range predict possibility of resonances in fluid-filled rock fractures. Study of Krauklis wave properties at laboratory scales requires evaluation of its propagation velocities in models with finite and thin elastic walls. Analysis of an exact solution for a fluid-filled trilayer with equal thickness plates reveals existence of the Krauklis waves in such a model, as well as another mode which propagates mostly in the solid part. Both propagation modes exist at all frequencies. We derived and verified various asymptotic solutions by comparing their dependencies on layer thicknesses and frequency with the exact numerical solution. Analytical and computational results demonstrate that in a 60-cmlong model, the first resonant frequency can be below 10 Hz. This result suggests that the Krauklis-wave effects can be studied in a laboratory at seismic range of frequencies avoiding a notorious problem of frequency downscaling. Strong dispersive properties of Krauklis waves and their dominant behavior in fluid-fracture systems are likely phenomena explaining the observed frequency-dependent seismic effects in natural underground reservoirs.

A novel hearing aid system based on bone-conducted ultrasonic (BCU) hearing is being developed for use by profoundly deaf people. However, the perception mechanisms involved in BCU hearing remain unclear. In this study, the way in which the mechanical frequency characteristics of human head vibration under BCU stimulation contribute to the hearing process was considered and examined in terms of the effects of the elasticity of the surface tissue that was in contact with a bone conduction vibrator. The results suggest that head vibration under BCU stimulation has low-pass filter-type characteristics with a cut-off frequency of between 30 and 40 kHz, which is attributed to the effects of the elasticity of living human skin. However, the issue of the psychoacoustic characteristics of the BCU hearing process not necessarily reflecting the mechanical frequency characteristics of head vibration remains. (C) 2014 The Japan Society of Applied Physics

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.