Takuya Hotehama

Modulation detection for amplitude-modulated bone-conducted sounds with sinusoidal carriers in the high- and ultrasonic-frequency range

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.

Propagation Velocity of Bone-Conducted Ultrasound in the Human Head

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 100 Hz steps with an interlateral phase difference from -2π to 2π in π/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.

Lateralization of amplitude‐modulated bone‐conducted ultrasounds: Discrimination of interaural time and intensity differences

Ultrasonic vibration generates a sensation of sound via bone conduction; the phenomenon is called bone‐conducted ultrasonic (BCU) hearing. Complex sounds also can be perceived by an amplitude‐modulated BCU (AM‐BCU). In this study, to investigate whether listeners can use an interaural time difference (ITD) in the amplitude envelope and an intensity difference (IID) as cues for lateralization, difference limens for an ITD (ITDL) and an IID (IIDL) for AM‐BCU were evaluated. Thirty‐kHz sine waves modulated by low‐passed noises with cutoff frequencies of 250, 500, 1000, 2000, and 4000 Hz were used as the AM‐BCU stimuli. ITDLs and IIDLs for air‐conducted (AC) low‐passed noises which correspond to modulator of the AM‐BCU were also evaluated. Both ITDLs and IIDLs for AM‐BCU were observed; AM‐BCU was larger in ITDL and smaller in IIDL than AC. The results suggest that it is possible to lateralize AM‐BCU using ITD in the envelope and/or IID; however, IID is a more effective cue than ITD.

Frequency characteristics of neuromagnetic auditory steady-state responses to sinusoidally amplitude-modulated sweep tones.

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 0.1-12.5kHz. 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 0.5kHz, and it decreased linearly on logarithmic scale toward lower and higher frequencies. Loudness model was plateaued between 0.5 and 4kHz. 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 0.5kHz and efficient neuronal processing at higher frequencies, which require less energy to retain equal perception.

Development of bone-conduction mobile phones: Assessment of hearing mechanisms by measuring psychological characteristics and acoustical properties in the outer ear canal

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.

Transient acceleration response of a bone-conducted ultrasonic pulse in living human head

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.

Development of a novel hearing-aid for the profoundly deaf using bone-conducted ultrasonic perception: Evaluation of transposed modulation

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.

Development of a novel hearing-aid for the profoundly deaf using bone-conducted ultrasonic perception: Assessments of the modulation type with regard to articulation, intelligibility, and sound quality

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf. We have developed a novel hearing-aid using BCU perception (BCU hearing aid: BCUHA) for the profoundly deaf. In the BCUHA, ultrasonic sinusoids of about 30 kHz are amplitude-modulated by speech and presented to the mastoid. Generally, two sounds are perceived: one is a high-pitched tone due to the ultrasonic carrier, with a pitch corresponding to a 8-16 kHz air-conducted (AC) sinusoid, and the other is the envelope of the modulated signal. As a method of amplitude modulation (AM), double-sideband with transmitted carrier (DSB-TC) modulation had been used, however, the DSB-TC modulation is accompanied by a strong high-pitched tone. In this study, two new AM methods, double-sideband with suppressed carrier (DSB-SC) and transposed modulations, that can be expected to reduce the high-pitched tone were newly employed in the BCUHA, and their resulting articulations, intelligibilities and sound qualities were evaluated. The results showed that DSB-TC and transposed modulation had higher articulation and/or intelligibility scores than DSB-SC modulation. Further, in terms of sound quality, the transposed speech was closer than other types of BCU speech to AC speech. These results provide useful information for further development of the BCUHA.

Psychoacoustic studies for development of the “binaural” Bone-Conducted Ultrasonic Hearing Aids

Ultrasound with a frequency greater than 20 kHz, which is generally recognized as a sound beyond the upper limit of human hearing, can be heard via bone-conduction. Such “audible” ultrasound through bone-conduction is referred to as bone-conducted ultrasound (BCU). It have been reported that profoundly hearing-impaired people can also hear a BCU and recognize part of the information on the modulating signal from the amplitude-modulated BCU. These perceptual characteristics were utilized in the development of a new hearing-aid system, Bone-Conducted Ultrasonic Hearing Aids (BCUHA), for the profoundly hearing-impaired. In this study, to verify the feasibility of “binaural” BCUHAs, we investigated whether listeners can use the interaural time differences in the amplitude envelopes (envelope-ITDs) and the intensity differences (IIDs) as cues for lateralization of BCUs. Results showed that listeners can detect changes in envelope-ITDs or IIDs of BCUs. Also, the discrimination thresholds of the polarities of IIDs were compensated by envelope-ITDs, i.e., the time-intensity trading was observed in the BCU perception. These findings indicate that the auditory system has the ability for lateralization using envelope-ITDs and IIDs of bilaterally presented BCUs. Further, it suggest that bilaterally presented BCUs are processed in the auditory pathway associated with lateralization in a similar manner to high-frequency amplitude-modulated sounds.

Sound source localization in the horizontal plane through the bilaterally applied bone-conducted ultrasonic hearing aids

Bone-conducted ultrasound (BCU) can be perceived not only by normal hearing but also by the profoundly hearing impaired who cannot make use of a conventional hearing aid. BCU hearing aid (BCUHA), in which an ultrasonic carrier is amplitude-modulated (AM) by collected external sound and presented through a bone-conduction vibrator onto the mastoid portion, has been developed for the profoundly hearing impaired. To obtain useful information in order to realize accurate sound source localization through the BCUHAs. In this study, localization performance in the horizontal plane through bilaterally applied BCUHAs was investigated by psychological experiments. Results show that subjects hardly lateralized when the BCUHAs were simply applied bilaterally with the double-sideband modulation method. On the other hand, the localization performances were improved when the inter-lateral intensity and time differences of presenting signals of BCUHAs were enhanced on the basis of those of the collected external sounds ...