Characterization and Prediction of Speech Intelligibility at the Output of Hearing Aids in a Noisy Working Environment.

Objective: Hearing aids are more and more technically advanced, but do not necessarily guarantee the reproduction of useful signals in all working environments. This is particularly the case for speech intelligibility. This study focuses on the prediction of hearing aid performance in the case of a moderate deafness setting, in service and industrial work environments. To improve intelligibility, hearing aids propose signal processing options such as noise reduction and compression. These processes can transform hearing aids into nonlinear systems. The aim of this study is to develop a nonlinear method for the characterization of hearing aids. Materials and Methods: The method is based on the synchronized swept sine (SSS) signal method.[16] The SSS method is applied for determining hearing aid frequency responses fitted according to the present methodology and several processing options. The characterization of hearing aid's program containing the noise reduction function is specifically analyzed. Indeed, to be fully active and efficient, the hearing aid, with the noise reduction feature activated, needs to be immersed in a noisy environment which does not allow nonlinear characterization. A linear approach is taken to study this feature. Three hearing aids commonly sold by hearing care professionals are studied here; all of them have three different programs. The characterization for each program is discussed. Results: The statistical study showed that the intelligibility, assessed using the speech transmission index in these sound environments, is well estimated for every program, although certain differences are observed when the compression effect is too high in the service work sector. Conclusion: The characterizations of hearing aids using the programs studied did not highlight the presence of frequency nonlinearities. The characterization method could not take into account amplitude nonlinearities when there is too much gain compression in the hearing process. Globally, all the hearing aid programs provided a very significant improvement in intelligibility in service and industrial work contexts.

A new device for real-time peroperative monitoring of ossicular chain reconstruction during middle ear surgery.

To limit functional surgical failure and reduce the rate of revision surgery in case of surgical ossicular chain reconstruction, a piezoelectric device was developed for assessment of ossicular chain vibrations during the middle ear surgery. The device resembled a pen and consisted of a reusable main body and a disposable sensitive head including piezoelectric polymer sensor. Almost all of components of the device were made of polymer for light weight and for acoustic impedance matching to the middle ear system. Several frequencies can be analyzed simultaneously and several measures can be taken by time. The results showed that the device can record normal and reconstructed ossicular chain vibration in response to an acoustic stimulation, with similar results to those achieved by laser Doppler vibrometer. This light, handheld and low-cost device allows fast, easy and safe assessments of normal ossicular chain mobility and ossicular chain reconstruction efficiency. Primary pre-clinical trial showed very promising performance of the device that could be used to qualitatively control ossiculoplasty during real-time surgical procedure. Clinical assessments will be done to further evaluate the real-life performance of the device.

Auditory fatigue among call dispatchers working with headsets.

OBJECTIVES: To determine whether call center dispatchers wearing headsets are subject to auditory fatigue at the end of a work shift. MATERIAL AND METHODS: Data was gathered at times when call centers were busiest. All call operators wore a headset for up to 12 h. Acoustic environment and noise exposure under the headset were continuously recorded during the entire work shift. Variations in auditory parameters were assessed using pure-tone air-conduction audiometry and an objective test based on distortion product otoacoustic emissions - contralateral suppression of distortion product otoacoustic emission (DPOAE) amplitudes (EchoScan test). Thirty-nine operators and 16 controls, all volunteers, were selected from 3 call centers (sales, assistance, and emergency) where all cognitive tasks were accomplished by phone and on computers. RESULTS: No acoustic shock was detected during the investigation. The highest normalized noise exposure (daily noise exposure level - LEX,8 h) measured was 75.5 dBA. No significant variation in auditory performances was detected with either pure-tone air-conduction audiometry or the EchoScan test. Nevertheless, dispatchers expressed a feeling of tiredness. CONCLUSIONS: For an equivalent diffuse field noise exposure, the use of a headset does not seem to worsen auditory fatigue for call center operators. The dispatcher's fatigue was probably due to the duration of the work shift or to the tasks they performed rather than to the noise exposure under a headset. Int J Occup Med Environ Health 2018;31(2):217-226.