中川 誠司

Several studies have reported that bone-conducted ultrasound (BCU) is even perceived by the profoundly sensorineural deaf however, the mechanisms involved remain unclear. We previously reported some unique characteristics of BCU perception that suggest unique neurophisiological mechanisms. For example: (1) the pitch of BCU is 10-odd kHz and is independent of its frequency (2) no beats occur between BCU and 10-odd-kHz air-conducted sinusoids (3) BCU masks 10-14 kHz air-conducted sounds and (4) the dynamic range of loudness for BCU is less than 20 dB. In the present study, several electrophysiological measurements were carried out to clarify the neural pathway involved in BCU perception. Specifically, auditory brainstem responses (ABRs), middle latency responses (MLRs), and cortical magnetic activities evoked by BCU were measured in humans. Substantial ABRs (wave I -V) and MLRs were evoked by BCU as well as air-conducted audible sound. In terms of cortical activities, clear N1m responses were elicited by BCU, with their sources being localized in the auditory cortices. However, BCU showed later, smaller, more posterior, and more lateral sources than audible-frequency sounds, and therefore did not appear to follow a tonotopic organization at the cortical level. These results indicate that: (1) the cochlea substantially contributes to BCU perception (2) BCU goes through the normal auditory pathway and there is no special organ for BCU perception and (3) some differences in the inner ear mechanisms may exist between audible sounds and BCU. © 2011 IEEE.

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.

カルバマゼピン（テグレトール^TM）の過量服薬による急性中毒に伴って伝導障害を呈した若年の症例を経験したので報告する。症例：20歳代，女性。境界型人格障害の診断で精神科へ通院中。衝動的にカルバマゼピン9,800mgを服用し，当院救命救急センターヘ搬送となった。来院時，高度意識障害と嘔吐を認め，気管挿管後に胃洗浄し集中治療室へ収容して人工呼吸器管理を行った。来院時心電図は正常であったが，カルバマゼピン血中濃度の上昇に伴い伝導障害がみられ，血中濃度の低下とともに正常化した。意識障害もカルバマゼピン血中濃度の低下とともに改善して第4病日には意識清明となり，第7病日精神科病院へ転院となった。結語：カルバマゼピンの過量服薬による急性薬物中毒の患者では，長期服用者や高齢・心疾患などの危険因子をもつ症例と同様に，経時的な血中濃度とECGの測定が必要と考えられた。

ある大きさの音を聞いていて，その後音の大きさが変化した時の脳磁界活動を解析した．音圧レベルの増加とともに脳磁界活動強度も増大したが，音圧レベルの減少に対して脳磁界活動強度はほとんど変化しなかった．

難聴が重篤になると従来型の補聴器の使用は困難になる.一方,骨伝導で呈示された周波数20,000Hz以上の高周波(骨導超音波)であれば,聴覚健常者はもとより重度難聴者にも知覚される場合があるが,その知覚メカニズムはほとんど未解明であった.我々は脳磁界計測(magnetoencephalography: MEG)によって骨導超音波が重度感音性難聴者にも音として知覚されること,骨導超音波を振幅変調することで音声伝達が可能であることを客観的に証明した.その上で,聴覚心理計測,神経生理計測,音響物理計測等を駆使した骨導超音波知覚メカニズムの解明と,骨導超音波知覚を応用した新型補聴器(骨導超音波補聴器)の開発に取り組んでいる.

難聴が重篤になると従来型の補聴器の使用は困難になる.一方,骨伝導で呈示された周波数20,000Hz以上の高周波(骨導超音波)であれば,聴覚健常者はもとより重度難聴者にも知覚される場合があるが,その知覚メカニズムはほとんど未解明であった.我々は脳磁界計測(magnetoencephalography: MEG)によって骨導超音波が重度感音性難聴者にも音として知覚されること,骨導超音波を振幅変調することで音声伝達が可能であることを客観的に証明した.その上で,聴覚心理計測,神経生理計測,音響物理計測等を駆使した骨導超音波知覚メカニズムの解明と,骨導超音波知覚を応用した新型補聴器(骨導超音波補聴器)の開発に取り組んでいる.

腰痛の原因が胸髄腫瘍であった1症例を報告する．62歳の女性で，腰痛と右鼠径部痛で治療を受けていたが，痛みは軽減しなかった．その後，右下肢の感覚障害が出現した．当科の初診時に明らかな間歇跛行はなく，両側のアキレス腱反射は軽度亢進していた．右下肢の運動障害があり，脱力が進行性であった．MRIでTh10の高さの脊髄内にガドリニウムで造影される結節状病変があった．手術で摘出した胸髄腫瘍の病理所見は肉芽腫であった．神経学的異常が進行性の腰痛では，脊髄腫瘍などの器質疾患の有無を判断するために，MRI等の画像診断を積極的に行うべきである．

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf. We have been developing a novel hearing-aid using BCU perception, which transmits a 30-kHz bone-conducted carrier that is amplitude-modulated by speech. The fundamental capabilities of the BCU hearing-aid (BCUHA) were objectively assessed by magnetoencephalography. Frequency- and temporal-resolution were assessed by measuring mismatch fields (MMFs). As well, the capability to discriminate two-channel BCUs presented to the left and right mastoids was verified by the laterality of auditory evoked magnetic field N1m. In the frequency-discrimination tests, amplitude-modulated BCU (AM-BCU) and air-conducted sound (AC) showed almost the same MMF-magnitudes when frequency/modulation-frequency of the standard-stimuli were 1.0 kHz, even though MMF-magnitudes for BCU were smaller than those of AC at 0.125 kHz. In the temporal-discrimination tests, MMFs for changes of stimulus-duration were measured. MMF-magnitudes for AM-BCUs reached more than 80% of those for air-conducted sounds (ACs). In addition, in the laterality-discrimination tests, N1m evoked by contralateral stimuli were larger in amplitude and shorter in latency than those evoked by ipsilateral stimuli for both AM-BCUs and ACs. This result agrees with earlier reports of AC auditions, and suggests that two-BCU channels presented to the left and right mastoid were separately localized. These findings objectively indicate that the BCUHA has practical frequency- and temporal resolution, and give a rationale for the development of a multi-channel (at least two) BCUHA.

難聴が重篤になると従来型の補聴器の使用は困難になる。一方、骨伝導で呈示された周波数20,000Hz以上の高周波(骨導超音波)であれば、聴覚健常者はもとより重度難聴者にも知覚される場合があるが、その知覚メカニズムはほとんど未解明であった。我々は脳磁界計測(magentoencephalography:MEG)によって骨導超音波が重度感音性難聴者にも音として知覚されること、骨導超音波を振幅変調することで音声伝達が可能であることを客観的に証明した。その上で、聴覚心理計測、神経生理計測、音響物理計測等を駆使した骨導超音波知覚メカニズムの解明と、骨導超音波知覚を応用した新型補聴器(骨導超音波補聴器)の開発に取り組んでいる。(著者抄録)

In recent years, the silence of hybrid cars is regarded as questionable from a viewpoint of pedestrian protection. This situation tends to obligate to add the car sound. In this study, we focused on half order spectrum and then subjective preference (subjective annoyance) of acceleration car sound for subjects who infrequently drive a car and who frequently drive it was evaluated. In addition, a sinusoidal model was adopt for acceleration car sound synthesis and the auditory impressions of car acceleration sound was examined using the psychological method and brain magnetic fields.

To clarify mechanisms of the bone-conducted ultrasonic (BCU) perception, tympanic membrane (TM) vibrations under BCU stimuli were measured in a human subject using a laser Doppler vibrometer (LDV). We presented a signal processing algorithm to increase the SNRs (signal-to-noise ratios) of measured LDV signals by removing only optical noise components from the wave signals. Further, we analyzed the TM vibrations using the presented method to investigate the contribution of nonlinear distortion in the BCU perception, i. e. the possibility of generating the audible subharmonics. As a result, we did not find any audible signals corresponding to the subjective pitch of BCU in the TM vibrations. This suggests that there is no evidence for nonlinear distortion in the outer and middle ear.

Engineers working in the engine rooms of ships are unable to communicate using normal speech. The engine room becomes a noise environment of engine and generators. To extract a normal speech produced in such noisy environments, we investigated construction of the body-conducted speech recognition system. Body-conducted speech is classified into solid propagated sound on skin or bone; thus it is not influenced by noise in the air. Body-conducted speech produces a low quality signal, because it does not include high frequency components of 2 kHz and greater. For this reason, many researchers have proposed signal retrieval methods, but conventional methods require both normal speech and body-conducted speech. In this paper, we propose the signal retrieval technique that does not require normal speech. First, the method converts the emphasized signal into body-conducted speech as a differential acceleration signal. Second, conventional noise reduction is applied to the emphasized signal to produce the retrieval signal. Our previous research investigated body-conducted speech under calm. The experiment confirmed the effectiveness of the new body-conducted speech retrieval technique, extracting in 98 dB SPL (-20 dB SNR). We conclude that the signal improves in sound quality on frequencies of 2 kHz and greater.

The production concept of car engine sounds has evolved from one of noise reduction to one of sound design. Auditory impressions have been examined from a psychological point of view. However, it is difficult to gain a full understanding of the issue using this approach alone. Thus, we investigated the relationships between subjective preference and brain magnetic fields for accelerating car interior noise. The acceleration noise was measured with an in-line 4-cylinder engine and harmonic complex tones that simulate acceleration noise used as the stimuli. Subjective evaluations were examined using the paired-comparison method. At the same time, the magnetoencephalography (MEG) alpha-waves range (8-13 Hz) measurements were made and analyzed using the ACF (autocorrelation function). The results indicate that the effective duration of the ACF of the MEGs of between 8 and 13 Hz lengthens after the presentation of a preferred sound.