Bone-conducted Ultrasound Research Articles

The effect of amplitude-modulation methods and speaker gender on monosyllable articulation by distantly-presented bone-conducted ultrasound

Bone-conducted ultrasound (BCU) can be heard and can transmit speech information using amplitude-modulation (AM). Additionally, BCU can be heard even on distal-parts of the body; e.g., the neck, trunk, and upper limbs. Since transmission path of the distantly-presented BCU is much longer and complicated than the ordinary-BCU presented to the head, it may contain tissues with strong nonlinearity like cartilages and generate some amount of self-demodulation components. Previous studies have indicated that the self-demodulation components contribute to improve the hearing of distantly-presented AM-BCU, however, self-demodulation components are thought to be affected by AM-methods and modulator characteristics. In this study, effects of the AM-methods and the speaker-gender on distantly-presented AM-BCU hearing were assessed by Japanese mono-syllable articulation testsin seven normal-hearing subjects. The articulation generally decreased as the presentation location moved away from the head, whereas the neck showed higher than the mastoid in some conditions. Effects of AM-methods on the articulationwere similarto those observed in the previous study on ordinary-BCU (DSB-TC ≒ Transposed ≫ SSB, DSB-SC). Also, female-voice showed higher articulation than male-voice, especially in the distal locations. The results suggested that self-modulation components have significant effect, although the AM-methods affect dominantly on hearing of the distantly-presented AM-BCU.

Characteristics of speech perception by distantly-presented bone-conducted ultrasound assessed by word intelligibility and monosyllable articulation tests.

High-frequency sounds above 20 kHz presented via bone conduction can be heard clearly and transmit speech information using amplitude modulation. Additionally, bone-conducted ultrasound (BCU) can be perceived even when the vibrator is presented to body parts distant from the head, such as the neck, arm, and trunk. To evaluate this previously presented BCU hearing, word intelligibility and monosyllable articulation tests were conducted in Japanese. The results suggested that a practical speech transmission, comparable to ordinary BCUs presented onto the head, can be obtained by distantly presented BCU.

Word Categorization of Vowel Durational Changes in Speech-Modulated Bone-Conducted Ultrasound.

Ultrasound can deliver speech information when it is amplitude-modulated with speech and presented via bone conduction. This speech-modulated bone-conducted ultrasound (SM-BCU) can also transmit prosodic information. However, there is insufficient research on the recognition of vowel duration in SM-BCU. The aim of this study was to investigate the categorization of vowel durational changes in SM-BCU using a behavioral test. Eight Japanese-speaking participants with normal hearing participated in a forced-choice behavioral task to discriminate between “hato” (pigeon) and “haato” (heart). Speech signal stimuli were presented in seven duration grades from 220 ms to 340 ms. The threshold at which 50% of responses were “haato” was calculated and compared for air-conducted audible sound (ACAS) and SM-BCU. The boundary width was also evaluated. Although the SM-BCU threshold (mean: 274.6 ms) was significantly longer than the ACAS threshold (mean: 269.6 ms), there were no differences in boundary width. These results suggest that SM-BCU can deliver prosodic information about vowel duration with a similar difference limen to that of ACAS in normal hearing.

Perception Mechanism of Bone-Conducted Ultrasound and Its Clinical Use.

It is generally believed that ultrasound cannot be heard. However, ultrasound is audible when it is presented through bone conduction. Bone-conducted ultrasound (BCU) has unique characteristics; the most interesting is its perception in patients with profound deafness. Some patients can perceive it and discriminate speech-modulated BCU. Previous reports have suggested that BCU can be used for a hearing aid or tinnitus sound therapy. In this review, the perception of BCU at both the peripheral and central levels was investigated based on previous studies, although some of them remain controversial. We also investigated the clinical use of BCU. To develop hearing aids utilizing BCU, the encoding of speech signals into BCU has to be established. The outcomes of the reported speech modulations were evaluated. Furthermore, the suppression of tinnitus by BCU was reviewed, and the feasibility of the application of BCU to tinnitus treatment was investigated.

Assessment of the difference limens for frequency, monosyllable articulation and word intelligibility by distantly-presented bone-conducted ultrasound.

Ultrasound can be clearly perceived by bone-conduction, and this "bone-conducted ultrasound (BCU)" can transmit speech information by using amplitude modulation (AM). Further, BCU can be perceived not only on the head but also on the distal parts of the body like the neck, trunk and arms. This "distantly-presented BCU" can be applied to the novel interface that can transmit sound information selectively to specific users who touches the vibrator. However, the ability to transmit sound information of distantly-presented BCU is unclear. First, to assess frequency discrimination ability, difference limens for frequency (DLFs) of the distantly-presented AM-BCU were measured with/without a low-pass masking noise that masked the self-demodulated components generated by the nonlinearity of biological tissues. DLFs comparable to that of air-conducted sounds were observed, whereas DLFs significantly increased above 1 kHz under the masking condition. These results suggest that practical frequency discrimination ability can be obtained even when BCUs were presented to distal body parts. Additionally, it is indicated that the demodulated components may contribute to transmitting frequency information above 1 kHz. Second, monosyllable articulation and word intelligibility tests were conducted in Japanese. The intelligibility and articulation at the neck were 55% and 38% respectively, whereas they decreased as the stimulus placement gets farther from the head. The results suggest the distantly-presented BCU device can be applied to transmission of speech information.

Self-demodulation characteristics of amplitude-modulated bone-conducted ultrasound in the human body presented to the neck, trunk and arm

Bone-conducted ultrasound (BCU) can be clearly perceived and can transmit speech information using amplitude-modulation (AM). BCU can also be perceived when presented to body parts like the neck, trunk and arms. When AM-BCUs propagate in the biological tissues with nonlinearity, like the cartilage, modulator signals may be self-demodulated. This demodulated-sound may affect BCU hearing. To examine the availability of the demodulated-components, difference limens for frequency (DLFs) were measured with/without the low-pass-masking noises that masked the demodulated-components. Practical frequency-discrimination ability was obtained even at distant body parts, whereas DLFs increased when the demodulation components were masked. Additionally, to elucidate the demodulation mechanisms in the human body, vibrations were measured around the cartilage. Significant demodulated-components were generated at especially the cartilage near the outer ear canal. These results indicated the availability of demodulated-components to improve hearing of the distantly-presented BCU, and provide useful information to optimize the novel BCU devices.

Propagation characteristics of amplitude-modulated bone-conducted ultrasound presented to the neck, trunk and arms

Bone-conducted ultrasound (BCU) is perceived even by the profoundly hearing impaired and a novel hearing aid has been developed. In the BCU hearing aid, the ultrasonic carrier is amplitude-modulated by speech signals and presented to the mastoid process of the temporal bone by a vibrator. However, BCU presented to parts of the body distant from the head can be perceived. In this study, vibration at the external auditory meatus was measured when amplitude-modulated BCU was presented to distal parts of the body. The results showed spectrum peaks corresponding to the carrier frequency (30 kHz) and the modulation frequency. The peak level of the carrier frequency tended to decrease depending on the distance between the external auditory meatus and the stimulation part basically. On the other hand, the peak level of the modulation frequency did not change with the distance between the external auditory meatus and the stimulation part, whereas the effect of modulation frequency was significant.

Measurements of vibration at the external auditory meatus and the upper limb in the living human body caused by distantly presented bone-conducted ultrasound

In bone conduction, vibrators are usually pressed onto the mastoid process, however, bone-conducted ultrasound (BCU) presented to body parts distant from the head can also be perceived. To elucidate mechanisms of the distantly presented BCU perception, transmissions of BCU were investigated on living human bodies. First, vibration at the external auditory meatus were measured when 30 kHz BCU was presented to distal parts. Second, vibrations of the upper limb were measured at nine surface points lined up straight from the forearm to shoulder when 30 kHz BCU was presented to nearby the wrist. The results showed that prominent spectrum peaks corresponding to the stimulus-frequency were observed at all parts. The vibration tended to decrease depending on the distance between the stimulus and measurement points, however, some exceptions existed. Efficiency of the BCU transmission seems to vary depending on factors like shape of the body, acoustical properties of the tissue, and coupling of the vibrator and the skin.

Temporal window of integration estimated by omission in bone-conducted ultrasound

Bone-conducted ultrasound (BCU) can be heard for both normal-hearing and some profoundly deaf individuals. Moreover, amplitude-modulated BCU can transmit the speech signal. These characteristics of BCU provide the possibility of the developing a bone-conducted ultrasonic hearing aid. Previous studies on the perception mechanism of speech-modulated BCU have pointed to the importance of temporal rather than frequency information. In order to elucidate the perception of speech-modulated BCU, further investigation is need concerning the processing of temporal information. The temporal processing of air-conducted audible sounds (ACASs) involves the integration of closely presented sounds into a single information unit. The long-temporal window of integration was estimated approximately 150–200 ms, which contribute to the discrimination of speech sound. The present study investigated the long-temporal integration system for BCU evaluated by stimulus omission using magnetoencephalography.Eight participants with normal hearing took part in this study. Ultrasonic tone burst with the duration of 50 ms and frequency of 30 kHz was used as the standard stimulus and presented with steady onset-to-onset times or stimulus-onset asynchronies (SOAs). In each sequence, the duration of the SOAs were set to 100, 125, 150, 175, 200, or 350 ms. For deviant, tones were randomly omitted from the stimulus train. Definite mismatch fields were elicited by sound omission in the stimulus train with an SOA of 100–150 ms, but weren’t with an SOA of 200 and 350 ms for all participants.We found that stimulus train for BCUs can be integrated within a temporal window of integration with an SOA of 100–150 ms, but are regarded as a separate event when the SOA is 200 or 350 ms in duration. Therefore, we demonstrated that the long-temporal window of integration for BCUs estimated by omission was 150–200 ms, which was similar to that for ACAS (Yabe et al. NeuroReport 8 (1997) 1971–1974 and Psychophysiology. 35 (1998) 615–619). These findings contribute to the elucidation and improvement of the perception of speech-modulated BCU.

Establishment of a cochlear injury model using bone-conducted ultrasound irradiation in guinea pigs and investigation on peripheral coding and recognition of ultrasonic signals

The cochlea of guinea pigs was irradiated with different frequencies of bone-conducted ultrasound (BCU) at a specific dose to induce cochlear hair cell-specific injuries, in order to establish frequency-related cochlear hair cell-specific injury models. Cochlear near-field potentials were then evoked using BCU of different frequencies and intensities to explore the peripheral coding and recognition of BCU by the cochlea. The inner ears of guinea pigs were irradiated by 30 kHz at 100 db and 80 kHz at100 db BCU for 6h to create frequency-related, ultrasound-specific cochlear injury models. Then, 30 kHz and 80 kHz BCU of different intensities were used to evoke auditory brainstem response (ABR) thresholds, compound action potential (CAP) thresholds, and action potential (AP) intensity-amplitude input-output curves in the normal control group and the ultrasonic cochlear injury group. This allowed us to explore the coding and recognition of BCU frequencies and intensities by cochlear hair cells. Immunofluorescence assay of outer hair cell (OHC) Prestin and inner hair cell (IHC) Otofelin was performed to verify the injury models. Irradiation of guinea pig inner ears by 30 kHz and 80 kHz BCU at a specific dose induced hair cell injuries at different sites. Irradiation with low frequency BCU mainly induced OHC injury, whereas irradiation with high frequency BCU induced IHC injury; moreover, IHC injury was more serious than OHC injury. The 30 kHz-evoked ABR threshold was significantly higher in the 30 kHz ultrasonic cochlear injury group compared to the normal control group. The 30 kHz-evoked ABR threshold was significantly higher in the 30 kHz ultrasonic cochlear injury group compared to the 80 kHz ultrasonic cochlear injury group. The difference in the 80 kHz-evoked ABR thresholds were not significant between the 30 kHz and 80 kHz ultrasonic cochlear injury groups. The click- and 30 kHz-evoked AP intensity-amplitude curves for the 30 kHz ultrasonic cochlear injury group indicate that the AP amplitude evoked at the same intensity was higher in the 30 kHz-evoked group than the click-evoked group. The spatial positions of cochlear hair cells in guinea pigs had a coding function for the frequencies of low-frequency ultrasound. OHCs have an amplification effect on the coding of low-frequency ultrasonic intensities. The peripheral perception of high frequency BCU may not require the participation of cochlear hair cells.

Assessments of basic properties of distal-presented bone-conducted ultrasonic hearing.

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf and a novel hearing aid using the perception of amplitude-modulated BCU (BCU hearing aid) has been developed. In the BCU hearing aid, the vibrator is pressed onto a part of the cranial bone behind the ear (mastoid process). However, BCU can be heard on distal parts of the body; i. e., the muscle of the neck, the clavicle, and the upper limb. In this study, to assess basic properties of such distal-presented BCU hearing, hearing thresholds were measured when 30-kHz tone bursts were presented to the neck and the upper and lower arms in normal hearing participants. Further, to assess the basic capability of transferring information by the distal-presented BCU hearing, temporal modulation transfer functions (TMTFs), that reflect the temporal resolution of the hearing, were estimated for 30-kHz carrier. The results showed that BCUs presented to the distal parts, including the lower arm, can be perceived at least in the normal hearing, whereas threshold increased depending on the distance from the head. Also, the temporal resolutions of the distal-presented BCU hearing at the neck, and the upper and lower arms were comparable to that of the mastoid process of the temporal bone. These results provide useful information not only for the improvement of the existing BCU hearing aid, but also for the development of novel distal-presented BCU devices that can provide sound information selectively to the specific person who touches the device by the arms or so.

Mechanisms of Bone-conducted Ultrasonic Perception Assessed by Measurements of Acoustic Fields in the Outer Ear Canal and Vibrations of the Tympanic Membrane.

Bone-conducted ultrasound (BCU) is even perceived by the profoundly sensorineural deaf; however, the mechanisms involved remain unclear. Acoustic fields in the external auditory meatus and vibrations of the tympanic membrane (TM) under BCU stimulation were measured to examine the generation of audible subharmonics in the bone-conduction transmission pathway. In the results, no significant audible-frequency signals were observed. These findings indicate that nonlinear distortions do not contribute to BCU perception and specific properties of BCU perception may be related to mechanisms in the cochlea or afferent neural pathway.

Assessment of detection threshold and temporal resolution of distantly presented bone-conducted ultrasonic hearing

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural hearing-impaired and has been applied to a novel hearing aid. The vibrator is usually pressed against a part of the cranial bone behind the ear (mastoid process); however, BCU presented to parts of the body distant from the head can be perceived. In this study, to assess the basic properties of distantly presented BCU hearing, hearing thresholds were measured when 30 kHz tone bursts were presented to the neck and the upper and lower arms in normal-hearing participants. Furthermore, temporal modulation transfer functions (TMTFs), which reflect the temporal resolution of hearing, were estimated for the distantly presented 30 kHz carrier. The results showed that BCU presented to parts of the body distant from the head, including the lower arm, can be perceived at least by normal-hearing persons, whereas the threshold increased depending on the distance from the head. Moreover, the temporal resolutions of the hearing of BCU distantly presented to the neck and the upper and lower arms were comparable to that distantly presented to the mastoid process of the temporal bone.

Outer hair cell function in human ultrasonic perception

Ultrasound can be heard by bone conduction. It is hypothesized that this bone-conducted ultrasound (BCU) is perceived in the basal turn of the cochlea and is a result of direct ultrasonic stimulation of inner hair cells via basilar membrane vibrations without cochlear amplifier. In order to clarify the contribution of outer hair cell function to ultrasonic perception, the present study evaluated changes in hearing sensitivity for BCU and air-conducted audible sound before and after ototoxic treatment. Twenty participants (40 ears) who were undergoing chemoradiation therapy with cisplatin participated in this study. After the treatment, 62.5% ears were diagnosed with hearing loss according to the criteria of the American Speech-Language-Hearing Association. The reduction of sensitivity to air-conducted audible sound occurred in the high-frequency range, which is thought to be important for ultrasonic perception. Surprisingly, BCU sensitivity was significantly improved after the treatment. These results suggest that direct ultrasonic stimulation of the cochlea, without audible sound generation, induces ultrasonic perception. The improvement of BCU sensitivity following the cisplatin administration may be explained by hypersensitivity associated with outer hair cells’ disorder.

An examination of the effects of broadband air-conduction masker on the speech intelligibility of speech-modulated bone-conduction ultrasound

Ultrasound can be heard by bone-conduction, and speech-modulated bone-conducted ultrasound (BCU) delivers the speech information to the human ear. One of the recognition mechanisms is the demodulation of the signals. Because some of the profoundly deaf can also hear speech-modulated BCU, another mechanism may also contribution to the recognition of speech-modulated BCU. In this study, eight volunteers with normal hearing participated. The intelligibilities of speech-modulated BCU were measured using a numeral word list under masking conditions. Because the masker can mask the demodulated sounds, the evaluation of the masking reveals the contribution of the demodulation to the recognition of speech-modulated BCU. In the current results, the masking of speech-modulated BCU differed from that of original non-modulated speech. Although the masking shifted the recognition curve for the original speech upward, the same results were not observed for the speech-modulated BCU. The masking generated the difference in the correct answers among the words for the speech-modulated BCU. The current results suggested the importance of the envelope of the modulated ultrasonic signal to the recognition under masking condition. Both demodulation and direct ultrasonic stimulation contribute to the recognition of speech-modulated BCU for the normal hearing individuals, and the direct ultrasonic stimulation plays an important role in the recognition for the profoundly deaf.

Residual inhibition of tinnitus induced by 30-kHz bone-conducted ultrasound

Sounds at frequencies of >24-kHz are classified as ultrasound which cannot be heard by humans if presented by air conduction, but can be perceived if presented by bone conduction. Some research studies involving ultrasonic hearing have reported that tinnitus is masked by bone-conducted ultrasound (BCU). However, little is known about residual inhibition (RI), which is a continuous reduction or disappearance of tinnitus after presentation of BCU. This study investigated whether RI could be induced by BCU. Five types of the masker sounds were used to measure RI in 21 subjects with tinnitus. A bone-conducted 30-kHz pure tone was used as a BCU, and an air-conducted 4-kHz pure tone, narrow-band noise, white noise, and a bone-conducted 4-kHz pure tone were used as controls of audible sounds. The masker intensities of the 30-kHz BCU and audible sounds were set at the minimum masking levels of tinnitus plus 3 and 10 dB, respectively, considering the narrow dynamic range of BCU. The duration of RI induced by the 30-kHz BCU was significantly longer than those induced by the 4-kHz sounds, but was not significantly different from that induced by the white noise. BCU activates the cochlear basal turn in response to the high frequency, which may broadly overlap with the frequency range that included the dominant tinnitus pitch in most of our subjects. The longer RI duration for the 30-kHz BCU was probably derived from this characteristic. These results suggested that the peripheral stimulation characteristic of BCU probably contributed to inducing long RI durations.

Evaluation of prosodic and segmental change in speech-modulated bone-conducted ultrasound by mismatch fields

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.

Development of a Bone-Conducted Ultrasonic Hearing Aid for the Profoundly Deaf: Evaluation of Sound Quality Using a Semantic Differential Method

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.

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 is accompanied by a strong high-pitched tone. In this study, two new AM methods, double-sideband with suppressed carrier (DSB-SC) and transposed modulation (TM), 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 TM had higher articulation and intelligibility scores than DSB-SC. Further, in terms of sound quality, the TM speech was closer than other types of BCU speech to AC speech. These results provide useful information for further development of the BCUHA.

Human ultrasonic hearing is induced by a direct ultrasonic stimulation of the cochlea

Ultrasound can be perceived by bone-conduction. The cochlear basal turn is involved in processing bone-conducted ultrasound (BCU) information. Previous studies have suggested that ultrasonic perception is induced by ultrasound itself. In contrast, it has also been suggested that a lower frequency sound is generated in non-linear process during the transmission pathway to the cochlea to induce an auditory sensations. To address this issue, we assessed cisplatin-induced changes in BCU sensitivity at 27, 30 and 33kHz in 20 participants (40 ears) who were scheduled to undergo cisplatin chemoradiation therapy. Following the treatment, 62.5% ears were diagnosed with hearing loss according to the criteria of the American Speech-Language-Hearing Association. As expected, significant increases in sensitivity threshold were observed for air-conducted sounds ranging from 8 to 14kHz. In contrast, the BCU threshold significantly decreased after the treatment. Considering that both air-conducted high-frequency sound and BCU are perceived in the cochlear basal turn, these findings indicate that ultrasonic perception is independent of hearing a lower frequency sound generated in non-linear process. In addition, our findings support the hypothesis that ultrasound itself induces ultrasonic perception in the cochlea. The observed cisplatin-induced increase in BCU sensitivity may be explained by hypersensitivity associated with outer hair cells’ disorder.