Ingrid Yeend

The National Acoustic Laboratories' procedure for selecting the saturation sound pressure level of hearing aids: experimental validation.

Objective: The primary aim of this study is to evaluate the accuracy of a new procedure for selecting the saturation sound pressure level (SSPL) of hearing aids. Secondary aims are to investigate what limits the minimum SSPL that is acceptable to clients and whether the type of limiting (peak clipping or compression limiting) affects the SSPL required. Design: The study comprised two experiments. In the first, subjects increased the SSPL of a laboratory master hearing aid until they experienced loudness discomfort and decreased it until the sound became less acceptable in some way. In the second study, subjects wore multi‐memory programmable hearing aids in their own environments and reported which of the two programs, differing only in SSPL setting, provided the more acceptable sound quality and comfort. Results: The theoretical procedure being investigated prescribed SSPLs that were within the acceptable range for 86% of the subjects in the laboratory study and for 63% of the subjects in the field experiment. On average, the theoretical predictions were neither too high nor too low. Incorporating individual measurements of loudness discomfort level into the prescription formula increased accuracy by such a small amount that it was not considered worthwhile. For a compression limiting hearing aid, the first thing that subjects noticed as SSPL was reduced was inadequate loudness. For the peak clipping hearing aid, however, both inadequate loudness and perception of distortion limited the acceptable SSPL range. Conclusion: The theoretical procedure provides a good initial prescription of three frequency average SSPL, but it is still essential to evaluate the fitting and, if necessary, fine tune the individuals hearing aid. Compression limiting hearing aids can have slightly lower SSPL settings than peak clipping hearing aids for the same acceptability.

The effect of frequency-dependent microphone directionality on horizontal localization performance in hearing-aid users.

Abstract Frequency-dependent microphone directionality alters the spectral shape of sound as a function of arrival azimuth. The influence of this on horizontal-plane localization performance was investigated. Using a 360° loudspeaker array and five stimuli with different spectral characteristics, localization performance was measured on 21 hearing-impaired listeners when wearing no hearing aids and aided with no directionality, partial (from 1 and 2 kHz) directionality, and full directionality. The test schemes were also evaluated in everyday life. Without hearing aids, localization accuracy was significantly poorer than normative data. Due to inaudibility of high-frequency energy, front/back reversals were prominent. Front/back reversals remained prominent when aided with omnidirectional microphones. For stimuli with low-frequency emphasis, directionality had no further effect on localization. For stimuli with sufficient mid- and high-frequency information, full directionality had a small positive effect on front/back localization but a negative effect on left/right localization. Partial directionality further improved front/back localization and had no significant effect on left/right localization. The field test revealed no significant effects. The alternative spectral cues provided by frequency-dependent directionality improve front/back localization in hearing-aid users. Sumario La direccionalidad de un micrófono frecuencia-dependiente altera la configuración espectral del sonido como función del azimuth de llegada. Se investigó la influencia de esto en el desempeño para la localización en el plano horizontal. Usando un sistema de altoparlante 360° y cinco estímulos con diferentes características espectrales, se midió el desempeño para la localización en 21 hipoacúsicos, sin usar auxiliares auditivos y con el apoyo de no direccionalidad, de direccionalidad parcial (de 1 y 2 kHz) y con direccionalidad total. Los esquemas de la prueba también se evaluaron en la vida cotidiana. Sin auxiliares auditivos, la precisión para localizar fue significativamente más pobre que los datos normativos. Debido a la inaudibilidad de la energía de altas frecuencias, las inversiones frente/atrás fueron prominentes. Las inversiones frente/atrás permanecieron prominentes cuando hubo apoyo con micrófonos omnidireccionales. Para estímulos con énfasis en frecuencias graves, la direccionalidad no tuvo un efecto adicional en la localización. Con estímulos cuya información de frecuencias medias y altas fue suficiente, la direccionalidad total tuvo un pequeño efecto positivo para la localización frente/atrás, pero un efecto negativo en la localización izquierda/derecha. La direccionalidad parcial mejoró adicionalmente la localización frente/atrás pero no tuvo un efecto significativo en la localización izquierda/derecha. La prueba de campo no mostró efectos significativos. Las claves espectrales alternativas proporcionadas por la direccionalidad frecuencia-dependiente, mejoraron la localización frente/atrás en usuarios de auxiliares auditivos.

Variation in preferred gain with experience for hearing-aid users

This study aimed to determine whether gain adaptation occurs, and at which frequency bands, among new hearing aid (HA) users. Fifty new and 26 experienced HA users were fitted with three listening programs (NAL-NL1 and NAL-NL1 with low- and high-frequency cuts) in the same hearing instrument family. Real-life gain preferences and comfortable loudness levels were measured one, four, and 13 months post-fitting for the new HA users, and one month post-fitting for the experienced HA users. Relative to experienced HA users, new HA users preferred progressively less overall gain than prescribed as the hearing loss became more severe. Gain adaptation occurred in new HA users with greater hearing loss, but was not complete 13 months post-fitting, and was not explained by changes in loudness perception. Preferences for a high-frequency gain cut by half of all study participants could not be predicted from audiological data. Gain adaptation management is recommended for new HA users with more than a mild hearing loss.

Validity and reliability of in-situ air conduction thresholds measured through hearing aids coupled to closed and open instant-fit tips

Abstract Audiometric measurements through a hearing aid (‘in-situ’) may facilitate provision of hearing services where these are limited. This study investigated the validity and reliability of in-situ air conduction hearing thresholds measured with closed and open domes relative to thresholds measured with insert earphones, and explored sources of variability in the measures. Twenty-four adults with sensorineural hearing impairment attended two sessions in which thresholds and real-ear-to-dial-difference (REDD) values were measured. Without correction, significantly higher low-frequency thresholds in dB HL were measured in-situ than with insert earphones. Differences were due predominantly to differences in ear canal SPL, as measured with the REDD, which were attributed to leaking low-frequency energy. Test-retest data yielded higher variability with the closed dome coupling due to inconsistent seals achieved with this tip. For all three conditions, inter-participant variability in the REDD values was greater than intra-participant variability. Overall, in-situ audiometry is as valid and reliable as conventional audiometry provided appropriate REDD corrections are made and ambient sound in the test environment is controlled. Sumario Las mediciones audiométricas a través de un auxiliar auditivo (‘in-situ’) pueden facilitar la prestación de servicios auditivos donde éstos son limitados. Este estudio investigó la validez y confiabilidad de los umbrales auditivos por conducción aérea in-situ, medidos con domos abiertos y cerrados, en relación a umbrales medidos con auriculares de inserción, y exploró las fuentes de variabilidad en la medición. Veinticuatro adultos con hipoacusia sensorineural asistieron a dos sesiones donde se midieron los valores de los umbrales y de la diferencia de oído real a marcación (REDD). Sin corrección, se midieron umbrales en dB HL para las bajas frecuencias significativamente más altos in-situ que con los auriculares de inserción. Las diferencias se debieron predominantemente a diferencias en la SPL del canal auditivo, conforme se midieron con el REDD, y se atribuyeron a fuga de energía en las bajas frecuencias. Los datos de test-retest rindieron una mayor variabilidad con el acoplamiento de domos cerrados, debido al sello inconsistente que se obtuvo con esta punta. Para las tres condiciones, la variabilidad entre los participantes en los valores REDD, fue mayor que la variabilidad intra-participantes. Globalmente, la audiometría in-situ es tan válida y confiable como la audiometría convencional, en la medida que se realicen correcciones REDD apropiadas y que haya control de sonido en el ambiente de evaluación.

Factors affecting reliability and validity of self-directed automatic in situ audiometry: implications for self-fitting hearing AIDS

BACKGROUND A reliable and valid method for the automatic in situ measurement of hearing thresholds is a prerequisite for the feasibility of a self-fitting hearing aid, whether such a device becomes an automated component of an audiological management program or is fitted by the user independently of a clinician. Issues that must be addressed before implementation of the procedure into a self-fitting hearing aid include the role of real-ear-to-dial difference correction factors in ensuring accurate results and the ability of potential users to successfully self-direct the procedure. PURPOSE The purpose of this study was to evaluate the reliability and validity of an automatic audiometry algorithm that is fully implemented in a wearable hearing aid, to determine to what extent reliability and validity are affected when the procedure is self-directed by the user, and to investigate contributors to a successful outcome. RESEARCH DESIGN Design was a two-phase correlational study. STUDY SAMPLE A total of 60 adults with mild to moderately severe hearing loss participated in both studies: 20 in Study 1 and 40 in Study 2. Twenty-seven participants in Study 2 attended with a partner. Participants in both phases were selected for inclusion if their thresholds were within the output limitations of the test device. DATA COLLECTION AND ANALYSIS In both phases, participants performed automatic audiometry through a receiver-in-canal, behind-the-ear hearing aid coupled to an open dome. In Study 1, the experimenter directed the task. In Study 2, participants followed a set of written, illustrated instructions to perform automatic audiometry independently of the experimenter, with optional assistance from a lay partner. Standardized measures of hearing aid self-efficacy, locus of control, cognitive function, health literacy, and manual dexterity were administered. Statistical analysis examined the repeatability of automatic audiometry; the match between automatically and manually measured thresholds; and contributors to successful, independent completion of the automatic audiometry procedure. RESULTS When the procedure was directed by an audiologist, automatic audiometry yielded reliable and valid thresholds. Reliability and validity were negatively affected when the procedure was self-directed by the user, but the results were still clinically acceptable: test-retest correspondence was 10 dB or lower in 97% of cases, and 91% of automatic thresholds were within 10 dB of their manual counterparts. However, only 58% of participants were able to achieve a complete audiogram in both ears. Cognitive function significantly influenced accurate and independent performance of the automatic audiometry procedure; accuracy was further affected by locus of control and level of education. Several characteristics of the automatic audiometry algorithm played an additional role in the outcome. CONCLUSIONS Average transducer- and coupling-specific correction factors are sufficient for a self-directed in situ audiometry procedure to yield clinically reliable and valid hearing thresholds. Before implementation in a self-fitting hearing aid, however, the algorithm and test instructions should be refined in an effort to increase the proportion of users who are able to achieve complete audiometric results. Further evaluation of the procedure, particularly among populations likely to form the primary audience of a self-fitting hearing aid, should be undertaken.

Evaluation of frequency compression and high-frequency directionality

Testing for hearing loss among farmers augusT 2010 • Vol. 63 • no. 8 Although the concept of frequency lowering has been around for at least four decades,1 it has recently seen a resurgence as a “hot topic” in amplification. In the past 2 years, it has been implemented in products from major hearing aid manufacturers, including Phonak. The goal of frequency lowering is to shift highfrequency sounds that cannot be adequately amplified by a hearing aid or used by the corresponding region of the cochlea to lower frequencies where the information can be better amplified or used. In particular, the feature is expected to assist in making available such important information as high-frequency speech sounds (e.g., /s/, /f/, /θ/) and frequencies between 2000 and 5000 Hz that are uniquely shaped by the pinna, depending on their angle of origin, to assist with front-back (F-B) discrimination. The frequency-lowering technique implemented in Phonak’s Naida product range (non-linear frequency compression, hereafter called frequency compression) affects only the frequency range above the frequencycompression threshold and is permanent. The compressed input range is consistently mapped to the output range, so wearers may be better able to adapt to the change in auditory stimulation than if the frequency lowering were transient. Extensive research was performed in developing Naida’s frequency compression and post-release using predominantly speech in quiet.2-6 However, its effect on horizontal localization and possible synergy with high-frequency directionality, a feature that has been demonstrated to improve F-B discrimination in users of behind-the-ear (BTE) hearing aids,7 has not been investigated. The study reported here was designed to explore the effect of frequency compression, high-frequency directionality, and the combination of the two on horizontal localization and speech recognition in noise.