Toshie Matsui

Benefit of a new hearing device utilizing cartilage conduction

OBJECTIVE Our previous study demonstrated that sound was effectively transmitted by attaching a transducer to the aural cartilage even without fixation pressure. This new method for sound transmission was found by Hosoi in 2004, and was termed cartilage conduction (CC). CC can be utilized even in hearing-impaired patients who cannot use air-conduction hearing aids owing to continuous otorrhea or aural atresia. A prototype hearing aid employing CC was investigated in this study. METHODS Four patients with conditions such as continuous otorrhea and acquired aural atresia after surgery participated in this study. The CC hearing aid was fitted, and its benefits were assessed by audiometric tests and interview. RESULTS Thresholds and speech recognition scores improved in all subjects. However, in subjects with continuous otorrhea, it was difficult to obtain the gains according to the target gains owing to their severe hearing loss and the limitation of the output level. On the other hand, unexpectedly large gains were obtained below 2kHz in the patient with acquired aural atresia. These large gains were probably caused by soft tissue filling the postoperative space. No subjects complained of pain associated with the attachment of the transducer, although such problems are usually observed for a bone-conduction (BC) hearing aid. This feature is considered one of the advantages of the CC hearing aid. CONCLUSION The results of the audiometric tests and interview suggest that the CC hearing aid has potential as a useful amplification device for hearing disability. Unfortunately, if the soft tissue pathway is not involved, the current device is insufficient for the patients with severe hearing loss. The improvement of the output level will lead to develop a reliable CC hearing aid as an alternative to BC hearing aids or bone anchored hearing aids.

Is cartilage conduction classified into air or bone conduction

The aim of this study was to establish the sound transmission characteristics of cartilage conduction proposed by Hosoi (2004), which is available by a vibration signal delivered to the aural cartilage from a transducer.

Cartilage conduction efficiently generates airborne sound in the ear canal

OBJECTIVE By attaching a transducer to the aural cartilage, a relatively loud sound is audible even with a negligibly small fixation force. Previous study has identified several pathways for sound transmission by means of cartilage conduction. This investigation focused on the relative contribution of direct vibration of the aural cartilage to sound transmission in an open and in an occluded ear. METHODS Thresholds with and without an earplug were compared for three experimental conditions: the transducer being placed on the tragus, pretragus, and mastoid. Eight volunteers with normal hearing participated. RESULTS The thresholds increased with distance of the transducer from the ear canal (tragus, pretragus, mastoid, in that order). The differences were statistically significant for all conditions except for the occluded ear at 4 kHz. With the earplug inserted, the thresholds for the tragus condition were most sensitive below 2 kHz, indicating a significant contribution of direct vibration of the aural cartilage. CONCLUSION Direct vibration of the aural cartilage can enhance sound transmission. At low frequencies, cartilage conduction can deliver sound efficiently across a blockage in the ear canal. Stray airborne sound radiating from the transducer dominates cartilage conduction in the open ear at high frequencies.

Activation of the left superior temporal gyrus of musicians by music-derived sounds.

Previous studies have suggested that professional musicians comprehend features of music-derived sound even if the sound sequence lacks the traditional temporal structure of music. We tested this hypothesis through behavioral and functional brain imaging experiments. Musicians were better than nonmusicians at identifying scrambled pieces of piano music in which the original temporal structure had been destroyed. Bilateral superior temporal gyri (STG) activity was observed while musicians listened to the scrambled stimuli, whereas this activity was present only in the right STG of nonmusicians under the same experimental conditions. We suggest that left STG activation is related to the processing of deviants, which appears to be enhanced in musicians. This may be because of the superior knowledge of musical temporal structure held by this population.

Advantages of cartilage sound conduction in hearing aids

A cartilage conduction hearing aid has been developed for patients who cannot use conventional hearing aids owing to particular diseases of the external or middle ear. A user of such a hearing aid places the ring-shaped transducer gently at the entrance of the external auditory canal, so that it does not cause any feeling of discomfort. The cartilage conduction transducer vibrates the aural cartilage of the user, and the transmitted vibration generates sound in the external auditory canal, particularly in the low and middle-frequency ranges. In this regard, the cartilage conduction hearing aid has a different principle of sound transmission from conventional hearing aids. In this study, the performance and possible advantages of cartilage sound conduction in hearing aids were examined. This was achieved through two experiments focusing on important indicators: (i) the susceptibility toward acoustic feedback compared with air sound conduction and (ii) the ability of the user to realize sound directivity during binaural use of the cartilage conduction hearing aid. It was found that cartilage conduction was less susceptible to acoustic feedback than air conduction through an open-fitting earplug, even though both the cartilage conduction transducer and the open-fitting earplug keep the external auditory canal open. With respect to the second experiment, the binaural use of cartilage conduction transducers was found to facilitate subjective lateralization for users when examined using the interaural intensity difference (IID) cue. These results show that the cartilage conduction hearing aid has distinct advantages over the conventional air conduction hearing aid in terms of the robustness against the acoustic feedback and effective binaural use. Although the cartilage conduction hearing aid was once considered merely an expedient alternative for patients suffering from particular diseases, the advantages highlighted in the present study may attract patients with mild and moderate hearing loss, who are currently using air conduction hearing aids.

Relationship between Intelligibility and autocorrelation factors of Japanese monosyllables

The amplification of speech sounds by hearing aids only partially improve speech intelligibility for sensorineural hearing loss. Previous research has identified the indiscernible consonants in Japanese monosyllables, but it remains unclear which acoustical features in those consonants cause hearing difficulty. Therefore, the aim of this study is to clarify the influential factors in speech intelligibility using the autocorrelation function (ACF), which can capture the temporal features of signals. We compared the ACF factors with the percent articulations obtained by a Japanese speech intelligibility test (n = 144). The time-series factors were calculated by running ACF along a monosyllable which then represented the median values of the ACF factors. Results showed the effective duration (τe [ms]) of the ACF was correlated with the averaged percent articulations among the consonants (r = 0.87, p < 0.01). Variable τe indicates the temporal fluctuation of speech signals including its fundamental frequency. Deteriorated perceptual function for temporal fluctuation may reduce recognition ability of the consonants, and thus the application of ACF analysis for hearing aids may help improve the hearing of patients with sensorineural hearing loss.

Speech intelligibility of hearing impaired participants in long-term training of bone-conducted ultrasonic hearing aid

Bone-conducted ultrasonic hearing aid (BCUHA) system is the unique device to provide the auditory sensation to profoundly hearing-impaired persons without any surgical operations. To clarify effects of long-term hearing training with this device, two deaf participants engaged the BCUHA training for 9 months. They were trained to use BCUHA through repetition of sentences read aloud and free conversation, and then they took part in word recognition tests and monosyllabic identification tests. Both participants showed that they could recognize words above chance using auditory sensation only provided by BCUHA device if alternatives or context were presented to them during the trials. Besides, it was observed that monosyllabic intelligibility score with both of auditory and visual cue had much increased with the day of training than the score with auditory cue only and that with visual cue only. The result suggests that the long-term training with BCUHA achieves efficient integration of auditory and visual cu...

Autocorrelation factors and intelligibility of Japanese monosyllables in individuals with sensorineural hearing loss

Some Japanese monosyllables contain consonants that are not easily discernible for individuals with sensorineural hearing loss. However, the acoustic features that make these monosyllables difficult to discern have not been clearly identified. Here, this study used the autocorrelation function (ACF), which can capture temporal features of signals, to clarify the factors influencing speech intelligibility. For each monosyllable, five factors extracted from the ACF [Φ(0): total energy; τ1 and ϕ1: delay time and amplitude of the maximum peak; τe: effective duration; Wϕ(0): spectral centroid], voice onset time, speech intelligibility index, and loudness level were compared with the percentage of correctly perceived articulations (144 ears) obtained by 50 Japanese vowel and consonant-vowel monosyllables produced by one female speaker. Results showed that median effective duration [(τe)med] was strongly correlated with the percentage of correctly perceived articulations of the consonants (r = 0.87, p < 0.01). (τe)med values were computed by running ACFs with the time lag at which the magnitude of the logarithmic-ACF envelope had decayed to -10 dB. Effective duration is a measure of temporal pattern persistence, i.e., the duration over which the waveform maintains a stable pattern. The authors postulate that low recognition ability is related to degraded perception of temporal fluctuation patterns.

Speech Intelligibility Prediction Based on the Envelope Power Spectrum Model with the Dynamic Compressive Gammachirp Auditory Filterbank.

In this study, we develop a new method to realize speech intelligibility prediction of synthetic sounds processed by nonlinear speech enhancement algorithms. A speech envelope power spectrum model (sEPSM) was proposed to account for subjective results on a spectral subtraction, but it is untested by recent state-of-the-art speech enhancement algorithms. We introduce a dynamic compressive gammachirp auditory filterbank as the front-end of the sEPSM (dcGC-sEPSM) to improve the predictability. We perform subjective experiments on speech intelligibility (SI) of noise-reduced sounds processed by the spectral subtraction and a recently developed Wiener filter algorithm. We compare the subjective SI scores with the objective SI scores predicted by the proposed dcGC-sEPSM, the original GT-sEPSM, the three-level coherence SII (CSII), and the shorttime objective intelligibility (STOI). The results show that the proposed dcGC-sEPSM performs better than the conventional models.

Analysis of acoustic features for speech intelligibility prediction models analysis of acoustic features for speech intelligibility prediction models

We have developed a new model to predict speech intelligibility of synthetic sounds processed by nonlinear speech enhancement algorithms. The model involves two recent auditory models: the dynamic compressive gammachirp (dcGC) auditory filterbank and the speech envelope power spectrum model (sEPSM). The dcGC-sEPSM was compared with commonly used prediction models based on perceptual intelligibility scores of speech sounds enhanced by classic spectral subtraction and state-of-the-art Wiener filtering. As a result, the dcGC-sEPSM predicted the scores better than the coherence SII (CSII), the short-time objective intelligibility (STOI), and the original sEPSM using the gammatone filterbank. There was, however, still inconsistency between the prediction and data. In this work, we show the analysis of acoustic features used in the prediction models. The CSII calculates the magnitude-squared coherence between clean and processed spectra to derive a signal-to-distortion ratio. The STOI calculates the correlation...