Tadao Okayasu

Peripheral perception mechanism of ultrasonic hearing

Ultrasound can be perceived by bone conduction, and its characteristics differ from those of air-conducted audible sound (ACAS) in some respects. Despite many studies on ultrasonic hearing, the details have not yet been clarified. In this study, to elucidate the perception mechanism, the masking of bone-conducted ultrasound (BCU) produced by ACAS and the sensitivity of BCU in hearing impaired subjects were evaluated. We found that BCU was masked by high frequency ACAS, especially in the frequency range of 10-14 kHz. The most effective masker frequency depended on masker intensity. For hearing impaired subjects, the pure tone thresholds at 1-8 kHz and the maximum audible frequencies at cut-off intensities of 70-100 dB HL were significantly associated with the BCU threshold (p < 0.01 or p < 0.05). No subjects with estimated total loss of the inner hair cell system in the cochlear basal turn could hear BCU. These results suggest the peripheral perceptual region to be located in the cochlea. The results of masking show the faster excitation spread to the lower frequency range, depending on the intensity. This faster excitation spread may be due to nonlinearity in cochlear mechanics, which may work even without cochlear amplifier, and induce unique characteristics of BCU.

Comparison between bone-conducted ultrasound and audible sound in speech recognition

Conclusion: This study showed that it is possible to transmit language information using bone-conducted ultrasound (BCU) in normal-hearing subjects. Our results suggest the possibility of a difference in speech recognition between BCU and air-conducted audible sound (ACAS). Objective: Ultrasound was audible when delivered by bone conduction. Some profoundly deaf subjects as well as normal-hearing subjects can discriminate BCU whose amplitude is modulated by different speech sounds. These findings suggest the usefulness of developing a bone-conducted ultrasonic hearing aid (BCUHA). However, the characteristics of BCU are still poorly understood. The aim of the present study was to compare BCU and ACAS in terms of their associated speech perception tendency and to investigate the different perceptual characteristics of BCU and ACAS. Subjects and methods: Speech discrimination tests using both BCU and ACAS were performed with normal-hearing subjects. BCU and ACAS were compared for intelligibility and hearing confusion. Results: With BCU, the maximum percentage correct totaled about 75%. Our comparison of the hearing confusion with ACAS and BCU according to the individual syllabic nuclear group showed a clear difference in the incorrect rates. In addition, the stimulus nuclear groups were often perceived in other nuclear groups in BCU.

Surgical results and psychological status in patients with intractable Ménière's disease

OBJECTIVES Mental disorder is often one of the causes to make treatments for Ménières disease more difficult. The aim in the present study is to examine ratios of the neurosis and depression in patients with intractable Ménières disease and also relationships between the ratios and surgical results after endolymphatic sac drainage with large doses of steroids. METHODS Between 1998 and 2009, we enrolled 263 intractable Ménières patients and divided into two groups, 207 in surgical group and 56 in non-surgical group. We used the Cornell Medical Index (CMI) and the Self-rating Depression Scale (SDS) at the diagnosis in our hospital to evaluate their psychological condition before treatments. CMI domains III and IV were defined as neurosis and SDS scores more than 40 as depression as a matter of convenience. Two years as well as seven years after surgery, patients with vertigo zero/month and hearing change>-10dB were evaluated in success group and the others in non-success group. RESULTS Neurosis and depression were diagnosed in approximately 40% and 60%, respectively, of intractable Ménières disease. Our results showed that surgical treatment significantly improved vertigo suppression and hearing gain in patients with no psychological symptoms compared with those exhibiting psychological symptoms both in surgical and non-surgical groups. Furthermore, surgical results in cases with mental disorder were superior to non-surgical results in cases without mental distress. CONCLUSIONS All taken together, psychological supports could be necessary for improving results both in the surgical and non-surgical treatments for patients with intractable Ménières disease. Some cases with intractable Ménières disease should really require additional surgical treatments even after psychological therapies.

Negative prognostic factors for psychological conditions in patients with audiovestibular diseases.

OBJECTIVE To examine the backgrounds of patients with audiovestibular disease regarding what influences their psychological state. METHODS During a 12-year period, 375 successive patients with audiovestibular diseases were enrolled in this study. Diseases included unilateral (n=174) and bilateral (n=51) Menières disease, sudden deafness with vertigo (n=70), and vestibular neuritis (n=80). Diagnosis, sex, age, duration of disease, vertigo frequency, persistent nystagmus, and ipsilateral/contralateral hearing levels were recorded. Cornell Medical Index (domains III-IV=neurosis) and Self-Rating Depression Scale (score>40=depression) were applied during acute vertigo remissions in all patients. RESULTS Neurosis and depression, respectively, were diagnosed in 62.7% and 82.4% of bilateral Menières, 32.7% and 48.9% of unilateral Menières, 15.7% and 38.6% of sudden deafness/vertigo, and 12.7% and 31.3% of vestibular neuritis patients. Multivariable logistic regression analysis showed that Menières disease with longer disease duration (Oz 1.212; P=0.021) and worse hearing in the secondary affected ear (Oz 1.131; P=0.042); sudden deafness/vertigo with persistent nystagmus (Oz 1.895; P=0.005); and vestibular neuritis with longer disease duration (Oz 1.422; P=0.019) and persistent nystagmus (Oz 1.950; P=0.0003) had mental illness significantly more often than those with shorter-duration disease, better hearing and no persistent nystagmus. CONCLUSION Mental disorder increased in accordance with solo vertigo, vertigo/hearing loss, repeated symptoms, and bilateral lesions. Treatment strategies should be carefully constructed for patients with persistent nystagmus, long disease duration, and hearing loss in the secondary affected ear to avoid psychological disorders.

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.

Magnetoencephalographic Study on Forward Suppression by Ipsilateral, Contralateral, and Binaural Maskers

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.

Duration-dependent growth of N1m for speech-modulated bone-conducted ultrasound

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.

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 sug...

Suppression of Subsequent N1m Amplitude When the Masker Frequency is Different from the Signal

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.

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.