Jürgen Kiessling

Adaptive Fitting of Hearing Instruments by Category Loudness Scaling (ScalAdapt)

The introduction of programmable as well as non-linear hearing instruments has shown that audiogram-based fitting procedures are inappropriate for meeting the individual needs of hearing aid users with sensorineural loss. Particularly the present and future development of hearing instruments with advanced analog and digital signal processing requires suitable fitting procedures. In this context, we developed an adaptive fitting strategy (ScalAdapt) using category loudness scaling. In this paper the procedure is described and tested using programmable 3-channel AGC instruments. However, it can be modified for any other hearing aid design. The underlying idea is to normalize the aided loudness perception for two input levels, one around the most comfortable level (MCL) and the other just below the uncomfortable level (UCL), as anchor points in each channel by interactive fine-tuning of the fitting parameters (channel gain, compression onset, compression ratio, etc.). The benefits of ScalAdapt have been evaluated by a field test study in 17 experienced hearing aid users. The results showed that ScalAdapt provides consistently higher objective (speech recognition in noise) and subjective benefits (self-assessment inventory) than for instance NAL-based fittings.

Hearing aid fitting procedures - state-of-the-art and current issues

The increasing degree of sophistication in hearing aid technology calls for appropriate fitting strategies, as otherwise hearing aid users cannot receive the full benefit from the most modern technological achievements. This paper describes the state of the art in hearing aid fitting procedures and offers a look into possible future developments. Currently, threshold-based fitting formula compete with loudness- and sound-based fitting procedures. Whereas threshold-based approaches are straightforward and timesaving, they do not consider loudness growth and the sound preferences of the listener. On the other hand, loudness- and sound-based procedures do take these aspects into account, but they are time consuming and it is not yet proven that they provide higher benefit for the end user. This may be due to the fact that either there is actually no extra benefit or more likely that the evaluation tools or study designs have to be improved. Concerns about how to fit more advanced future hearing instruments seem to be inappropriate, as an analysis of possible future signal processing algorithms shows that they probably do not need extra fitting to the individual hearing impairment but rather need optimization according to the acoustical environment.

Benefit of a digital feedback suppression system for acoustical telephone communication.

Because hearing instruments have traditionally performed poorly during acoustical telephone use, the benefit of using a Digital Feedback Suppression (DFS) system for acoustical telephone communication was evaluated. For this purpose a special speech test based on the method and material of the Oldenburg Sentence Test was developed, presenting the speech signal via a telephone receiver. The correct coupling of the receiver and the hearing aid was monitored by means of a probe microphone. The word score was determined for two different settings of the hearing aid: (1) DFS activated (2) DFS deactivated. The difference in word score between these two conditions is an indication of the benefit provided by the DFS system. For almost all subjects, speech recognition at the telephone could be improved using the DFS system. This is a significant contribution in increasing end-user overall satisfaction with hearing aids.

A fitting strategy for digital hearing aids based on loudness and sound quality

In order to find an adequate fitting strategy for digital compression hearing aids a combination of two interactive fitting strategies was developed, one of these based on frequency specifice loudness (ScalAdapt) and the other based on overall loudness and on sound quality (Cambridge Procedure). This new fitting strategy was tested against the sound and overall loudness based strategy and against a prescriptive fitting strategy in a 2-weeks field test with questionnaires and in laboratory measurements, subjectively as well as objectively. With six sensorineural hearing impaired participants no straightforward results were achieved. Additionally, the different testing procedures indicate (in tendency) different fitting strategies to be superior. More subjects will have to be tested and innovative evaluation methods have to be considered.

Fitting strategies and candidature criteria for unilateral and bilateral hearing aid fittings

In this paper, hearing aid fitting strategies are reviewed and candidature criteria for unilateral and bilateral fittings are discussed. Fitting strategies are primarily governed by the objectives of hearing aid fitting that can be set in different ways. Based on common goals, fitting strategies can be broken down into three stages: (1) basic fitting, (2) fine-tuning and (3) verification and validation. A fine-tuning concept basing on so-called meta-controllers is described and the issue of bilateral fitting strategies is discussed. In a first order approach, bilateral hearing aids can be fitted in parallel as unilateral aids, followed by bilateral fine-tuning, making sure that loudness is balanced and overall loudness is accepted. Parallel fitting of bilateral aids is more favourable than sequential fitting to avoid rejection because of a negative experience with unilateral amplification due to difficulties in disadvantageous listening situations. Candidature criteria are presented by means of a flow chart structuring the decision making process and arriving at the conclusion that bilateral fitting should be considered the normal case. If there is any doubt about the benefit of bilateral fitting, a trial with bilateral aids should be performed.

Modeling Relationships between Various Domains of Hearing Aid Provision

Various inventories have been developed to quantify the success of hearing aid provision. Though numerous parameters including initial measures (hearing disability, handicap) or ‘outcome measures’ (e.g. benefit, satisfaction and usage) are recorded, relationships and interactions among them are still unclear. A study applying a questionnaire addressing 11 domains relevant to amplification was conducted in order to generate different psychometric models with the AMOS© software package for structural equation modeling. The models expose easily interpretable interactions and are helpful in understanding effects occurring with commonly used outcome measures: benefit reflects the difference between the aided and unaided condition but additionally comprises the importance of the hearing aid within a specific situation. Satisfaction is highly reliant on benefit. Usage is strongly dependent on the severity of hearing problems and therefore not appropriate in assessing the success of amplification. Moreover, the models help to predict the outcome of clinically used inventories (i.e. the Glasgow Hearing Aid Benefit Profile).

Clinical Evaluation of a Programmable Three-Channel Automatic Gain Control Amplification System

This paper reports on the clinical evaluation of a commercially available head-worn programmable 3-channel automatic gain control (AGC) hearing instrument (Siemens, Triton 3000). A preliminary fitting procedure is developed for the 3-channel AGC amplification system, which is compared by 26 experienced hearing instrument wearers with their own single-channel AGC instruments. The benefits of both amplification systems are assessed by speech audiometry at different signal-to-noise ratios utilizing German rhyme test speech material. In addition, subjective judgements concerning sound quality, speech intelligibility and comparison with the subjects own instrument are evaluated. The results indicate that the multichannel compression instrument is superior to single-channel aids in competitive speech situations. If the 3-channel AGC instrument is used as an automatic noise reduction system in patients requiring a certain amount of low-frequency gain, a markedly better speech recognition can be achieved compared to the subjects personal aids.

Functionality of hearing aids: state-of-the-art and future model-based solutions

Abstract A review about technical and perceptual factors in hearing aid technology, research and development is provided, covering current commercial solutions, underlying models of hearing loss for usage in hearing devices and emerging future technical solutions for hearing aid functionalities. A chain of techniques has provided incremental, but steady increases in user benefit, e.g. in the fields of hearing aid amplification, feedback suppression, dynamic compression, noise reduction and situation adaptation. The models describing the perceptual consequences of sensorineural hearing impairment describe the effects on the acoustical level, the neurosensory level and the cognitive level and provide the framework for compensatory (or even substitutional) functions of hearing aids in terms of the attenuation component, the distortion component and the neural component of the hearing loss. A major factor is the requirement of a strong individualisation of hearing aid solutions calling for an appropriate assessment of the different sensorineural components of a hearing loss, especially with respect to bilateral and binaural hearing aid solutions.

Technische Hilfsmittel zur Rehabilitation von Hör- und Kommunikationsstörungen

HAufig ist eine HOrgerAteversorgung allein nicht ausreichend, um im Altag alle HOr- und Kommunikationssituationen zu bewAltigen. Daher werden zusAtzliche technische Hilfsmittel notwendig. Es wird ein Uberblick Uber verschiedene Systeme und GerAte gegeben, in dem die verschiedenen Kommunikationsmittel dargestellt und durch Beispiele belegt werden. In ErgAnzung zu HOrgerAten wird auf den Audioeingang, auf die Induktions-/Telefonspule sowie auf drahtlose Kommunikationshilfen und ZubehOr fUr Radio und Fernsehen eingegangen. Zu den Kommunikationshilfen, die ohne HOrgerAt Verwendung finden, gehOren Infrarotanlagen, ZubehOr fUr Telefon und TUrklingel, ZusatzgerAte und Hilfsmittel fUr das Telefon sowie verschiedene Therapiehilfen bei HOr- und SprechstOrungen. Auf diverse Formen der HOrhilfen, wie vibrotaktile Systeme, Kochleaimplantate und Mittelohrimplantate wird abschliessend ebenfalls verwiesen. Unter BerUcksichtigung der Heil- und Hilfsmittelrichtlinien werden Aspekte zur Verordnung der hier vorgestellten HOr- und Kommunikationshilfen diskutiert.

Comparison of single-microphone noise reduction schemes: can hearing impaired listeners tell the difference?

Abstract Objective: The perceived qualities of nine different single-microphone noise reduction (SMNR) algorithms were to be evaluated and compared in subjective listening tests with normal hearing and hearing impaired (HI) listeners. Design: Speech samples added with traffic noise or with party noise were processed by the SMNR algorithms. Subjects rated the amount of speech distortions, intrusiveness of background noise, listening effort and overall quality, using a simplified MUSHRA (ITU-R, 2003) assessment method. Study sample: 18 normal hearing and 18 moderately HI subjects participated in the study. Results: Significant differences between the rating behaviours of the two subject groups were observed: While normal hearing subjects clearly differentiated between different SMNR algorithms, HI subjects rated all processed signals very similarly. Moreover, HI subjects rated speech distortions of the unprocessed, noisier signals as being more severe than the distortions of the processed signals, in contrast to normal hearing subjects. Conclusions: It seems harder for HI listeners to distinguish between additive noise and speech distortions or/and they might have a different understanding of the term “speech distortion” than normal hearing listeners have. The findings confirm that the evaluation of SMNR schemes for hearing aids should always involve HI listeners.