(Why) Do Transparent Hearing Devices Impair Speech Perception in Collocated Noise?

Hearing aids and other hearing devices should provide the user with a benefit, for example, compensate for effects of a hearing loss or cancel undesired sounds. However, wearing hearing devices can also have negative effects on perception, previously demonstrated mostly for spatial hearing, sound quality and the perception of the own voice. When hearing devices are set to transparency, that is, provide no gain and resemble open-ear listening as well as possible, these side effects can be studied in isolation. In the present work, we conducted a series of experiments that are concerned with the effect of transparent hearing devices on speech perception in a collocated speech-in-noise task. In such a situation, listening through a hearing device is not expected to have any negative effect, since both speech and noise undergo identical processing, such that the signal-to-noise ratio at ear is not altered and spatial effects are irrelevant. However, we found a consistent hearing device disadvantage for speech intelligibility and similar trends for rated listening effort. Several hypotheses for the possible origin for this disadvantage were tested by including several different devices, gain settings and stimulus levels. While effects of self-noise and nonlinear distortions were ruled out, the exact reason for a hearing device disadvantage on speech perception is still unclear. However, a significant relation to auditory model predictions demonstrate that the speech intelligibility disadvantage is related to sound quality, and is most probably caused by insufficient equalization, artifacts of frequency-dependent signal processing and processing delays.

Occlusion and coupling effects with different earmold designs - all a matter of opening the ear canal?

OBJECTIVE: Ear canal occlusion by a hearing aid leads to an unnatural sound of the own voice due to a level increase of bone-conducted low-frequency components of the ear canal. Opening the ear through vents or domes reduces this so-called occlusion effect, however at the cost of reduced hearing aid performance. For individual earmolds, several other design options to reduce the occlusion effect have been proposed but not reliably evaluated. DESIGN: The occlusion effect and coupling parameters were assessed through subjective ratings and real-ear measurements. STUDY SAMPLE: Six individual earmold designs, each with different venting options, were tested in 10 subjects. RESULTS: In line with previous studies, our data show that the opening of the ear as described by the acoustic mass of the vent is the prime parameter that predicts both the occlusion effect and coupling parameters. However, the design of the earmold, most importantly the location where sealing of the ear canal is achieved, is another important factor for occlusion and coupling effects. CONCLUSIONS: Although no reduction of the occlusion effect seems possible without additional opening of the ear canal, some earmold modifications seem to aggravate the occlusion effect as compared to a standard earmold with equivalent vent.

[(Air-conduction) Hearing aids-indication, designs and applications : Signal processing and importance of individual fitting]. / (Luftleitungs­)Hörsysteme ­ Indikation, Bauformen und Einsatzmöglichkeiten : Signalverarbeitung und die Bedeutung der individuellen Anpassung.

Many people in Germany and worldwide suffer from a reduced communication ability due to impaired hearing. Especially older people are affected. Hearing aids, which pick up ambient sounds, process them, and output airborne sound in the ear canal, can help in most cases. These so-called air-conduction hearing aids are commonly used to compensate for hearing loss and are described in more detail in this article. To this end, indications, differences to other hearing aids and implants, various designs, the importance of individual ear coupling, features of the signal processing, and the importance of the individual hearing aid fitting are explained in detail.

Design and verification of a measurement setup for wireless remote microphone systems (WRMSs).

OBJECTIVE: This work presents the design and verification of a simplified measurement setup for wireless remote microphone systems (WRMSs), which has been incorporated into guidelines of the European Union of Hearing Aid Acousticians (EUHA). DESIGN: Three studies were conducted. First, speech intelligibility scores within the simplified setup were compared to that in an actual classroom. Second, different WRMSs were compared in the simplified setup, and third, normative data for normal-hearing people with and without WRMS were collected. STUDY SAMPLE: The first two studies include 40 older hearing impaired and the third study 20 young normal-hearing adults. RESULTS: Speech intelligibility with WRMS was not different across actual classroom and simplified setup. An analog omnidirectional WRMS showed poorer speech intelligibility and poorer quality ratings than digital WMRSs. The usage of a WRMS in the simplified setup resulted in significantly higher speech intelligibility across all tested background noise levels. CONCLUSIONS: Despite being a simplified measurement setup, it realistically emulates a situation where people are listening to speech in noise from a distance, such as in a classroom or meeting room. Hence, with standard audiological equipment, the individual benefit of WRMSs can be measured and experienced by the user in clinical practice.

Evaluation of Noise Reduction Algorithms in Hearing Aids for Multiple Signals From Equal or Different Directions.

One objective way to evaluate the effect of noise reduction algorithms in hearing aids is to measure the increase in signal-to-noise-ratio (SNR). To this end, Hagerman and Olofsson presented a method where multiple recordings take place and the phase of one signal is inverted between the measurements. This phase inversion method allows one to separate signal and noise at the output of the hearing aid so that the increase in SNR can be evaluated. However, only two signals can be distinguished, for example, speech and noise. As many realistic situations include more than two signals, we extend the method to an arbitrary number of signals. Two different approaches are discussed. For the first one, groups of the signals are created and presented in such a way that the basic phase inversion method can be used. The second, more efficient approach defines a linear system of equations considering all signals. As the robustness of this approach depends on the structure of the system matrix, the design of this matrix is described in detail. To prove the concept, the proposed efficient method was applied to a setup in which nine different signals were presented by eight loudspeakers, and an analysis of errors was performed. With this setup, a state-of-the-art hearing aid was analyzed for four different settings, that is, with the digital noise reduction or the directional microphones turned on or off. As a result, the SNRs for all directions can be investigated individually.