Richard C. Seewald

The Desired Sensation Level Multistage Input/Output Algorithm

The Desired Sensation Level (DSL) Method was revised to support hearing instrument fitting for infants, young children, and adults who use modern hearing instrument technologies, including multichannel compression, expansion, and multimemory capability. The aims of this revision are to maintain aspects of the previous versions of the DSL Method that have been supported by research, while extending the method to account for adult-child differences in preference and listening requirements. The goals of this version (5.0) include avoiding loudness discomfort, selecting a frequency response that meets audibility requirements, choosing compression characteristics that appropriately match technology to the users needs, and accommodating the overall prescription to meet individual needs for use in various listening environments. This review summarizes the status of research on the use of the DSL Method with pediatric and adult populations and presents a series of revisions that have been made during the generation of DSL v5.0. This article concludes with case examples that illustrate key differences between the DSL v4.1 and DSL v5.0 prescriptions.

Clinical Protocols for Hearing Instrument Fitting in the Desired Sensation Level Method

A discussion of the protocols used particularly in the clinical application of the Desired Sensation Level (DSL) Method is presented in this chapter. In the first section, the measurement and application of acoustic transforms is described in terms of their importance in the assessment phase of the amplification fitting process. Specifically, the implications of individual ear canal acoustics and their impact on accurately defining hearing thresholds are discussed. Detailed information about the statistical strength of the real-ear-to-coupler difference (RECD) measurement and how to obtain the measure in young infants is also provided. In addition, the findings of a study that examined the relationship between behavioral and electrophysiologic thresholds in real-ear SPL is described. The second section presents information related to the electroacoustic verification of hearing instruments. The RECD is discussed in relation to its application in simulated measurements of real-ear hearing instrument performance. In particular, the effects of the transducer and coupling method during the RECD measurement are described in terms of their impact on verification measures. The topics of insertion gain, test signals, and venting are also considered. The third section presents three summary tables that outline the hearing instrument fitting process for infants, children, and adults. Overall, this chapter provides both clinical and scientific information about procedures used in the assessment and verification stages of the DSL Method.

Comparison of linear gain and wide dynamic range compression hearing aid circuits: aided speech perception measures.

OBJECTIVES The goal of this study was to test the theoretical advantages of a single-channel wide dynamic range compression (WDRC) circuit for speech intelligibility and loudness comfort for five speech spectra. DESIGN Twelve adolescents and young adults with moderate to severe hearing loss were fitted with the Siemens Viva 2 Pro behind-the-ear instrument set to DSL 4.0 targets for both linear gain and WDRC processing. Speech intelligibility was measured in the unaided, linear gain and WDRC conditions using two tasks in quiet: nonsense words and sentences. The items were digitally filtered to represent five speech spectra: average speech at 4 m, average speech at 1 m, own voice at ear level, classroom at 1 m, and shouted speech at 1 m. The subjects also rated the loudness of each hearing aid/speech spectrum combination using a categorical rating scale. RESULTS Both the linear gain and WDRC settings provided improved speech recognition relative to the unaided condition, and the two circuits resulted in equivalent performance for average speech input levels. On average, the WDRC aid resulted in high and uniform speech recognition scores across the five spectra. In contrast, the linear gain aid resulted in a lower recognition score for soft speech and shouted speech relative to that obtained with an average speech level. Analysis of individual speech recognition benefit scores revealed that 11 out of 12 subjects had equal or greater performance with the WDRC processing than the linear processing. Subjective loudness ratings in the linear gain condition were compatible with decreased sensation level for soft speech and loudness discomfort for shouted speech. CONCLUSIONS WDRC processing has potential applications in hearing aid fittings for listeners with moderate to severe hearing loss because it provides a consistently audible and comfortable signal across a wide range of listening conditions in quiet without the need for volume control adjustments.

Selecting amplification characteristics for young hearing-impaired children.

The task of selecting the electroacoustic characteristics of hearing aids for young hearing-impaired children continues to challenge many clinical audiologists. The rationale for a theoretically based approach to this problem is presented. Additionally, issues related to the choice of an idealized speech spectrum for a theoretical selection model are considered in relation to the acoustic environment and auditory needs of young hearing-impaired children. Finally, the preliminary version of a computer assisted speech spectrum approach, which facilitates the initial selection of frequency/gain and frequency/SSPL characteristics is presented.

The DSL Method for Pediatric Hearing Instrument Fitting: Historical Perspective and Current Issues

The Desired Sensation Level (DSL) Method was originally developed in the early 1980s to provide clinicians with a systematic, science-based approach to pediatric hearing instrument fitting that ensures audibility of amplified speech by accounting for factors that are uniquely associated with the provision of amplification to infants and young children who have hearing loss. This review identifies and describes several of the primary factors that have been considered in the development of the DSL Method. Specifically, the issues discussed relate to: (1) the definition and measurement of relevant acoustic, electroacoustic and audiometric variables; (2) how the external ear acoustics of infants and young children are accounted for in the DSL Method for both audiometric assessment and in the fitting of amplification; and (3) how the DSL Method has evolved concurrently with developments in hearing instrument and electroacoustic measurement technologies. Finally, current issues in the field are identified that have motivated the development of version 5.0 of the DSL Method for hearing instrument fitting.

Ear level recordings of the long-term average spectrum of speech.

The long-term average speech spectrum (LTASS) was measured at two different recording positions: 30 cm directly in front of the talker (reference position), and at the tragus of the talkers ear (ear-level position), for three groups of subjects: adult males, adult females, and children. Results indicated significant differences in the overall level and frequency spectra between the LTASS obtained at each microphone location. For all three groups of subjects the LTASS measured at the ear-level position consisted of more low frequency energy (i.e., below 1000 Hz) and less high frequency energy (i.e., above 2500 Hz) than did the LTASS measured at the reference microphone position. The findings suggest that the algorithms currently used to prescribe hearing aid gain may underestimate the sensation level of a hearing-impaired individuals own amplified speech productions at frequencies below 1000 Hz and overestimate the sensation level of a talkers own speech above 2500 Hz. The implications of these findings concerning selection of the electroacoustic characteristics of an amplification system for hearing-impaired individuals are discussed.

Protocol for the provision of amplification within the Ontario Infant hearing program

Abstract This document describes the protocol for the provision of amplification to infants and preschool children registered with the Ontario infant hearing program (OIHP) in Canada. The provision of amplification includes the prescription and dispensing of hearing instruments to infants and preschool children identified with permanent childhood hearing impairment (PCHI) in the province of Ontario. The first section deals with the structure and processes of the program, while the second section specifies the clinical procedures that are applied in providing hearing instruments to infants and young children with hearing impairment. Sumario Este documento describe el protocolo para el suministro de amplificación a niños y preescolares registrados en el programa de audición infantil de Ontario (OIHP) en Canadá. El suministro de amplificación incluye la prescripción y entrega de instrumentos auditivos a niños y a preescolares identificados con discapacidad infantil auditiva permanente (PCHI) en la provincia de Ontario. La primera sección trata sobre la estructura y los procesos del programa, mientras que la segunda sección, especifica los procedimientos clínicos que se aplican para suministrar instrumentos auditivos a bebes y ninos pequeños con discapacidad auditiva.

Comparison of linear gain and wide dynamic range compression hearing aid circuits II : Aided loudness measures

Objectives: The goal of this study was to test the theoretical advantages of a single‐channel wide dynamic range compression (WDRC) circuit fitted using the DSL method for increased dynamic range and normalized loudness growth. Design: Ten adolescents and young adults with moderate to severe sensorineural hearing loss were fitted monaurally with the Siemens Viva 2 Pro behind‐the‐ear instrument set to DSL 4.0 targets for both linear gain and WDRC processing. Threshold, upper limit of comfort and loudness growth were measured in the unaided, linear gain and WDRC conditions for warble tones, environmental sounds and speech. Twelve adult listeners with normal hearing also were tested monaurally in the unaided condition to provide normative data for comparison purposes. Results: The WDRC hearing aid provided a greater input dynamic range than the linear circuit for all stimuli. The dynamic range was normalized for more subjects with the WDRC than the linear hearing aid. In addition, exponential loudness growth functions fitted to the loudness growth data showed that, on average, loudness growth was more normalized with the WDRC hearing aid fitted to DSL[i/o] targets than the linear hearing aid fitted to DSL[i/o] targets. Conclusions: WDRC processing, fitted using the DSL[i/o] method, has potential applications in hearing aid fittings for listeners with moderate to severe hearing loss because it provides an audible, comfortable and tolerable amplified signal across a wider range of inputs than linear gain processing, without the need for volume control adjustments.

Validity and Repeatability of Level-independent Hl to Spl Transforms

Objective: The purpose of this study was to evaluate the reliability and validity of the real ear to coupler difference (RECD) and the real ear to dial difference (REDD) in predicting real ear SPL (RESPL). Design: The RESPL, RECD, and REDD were measured in the right ear of 24 normal‐hearing subjects using probe microphone equipment and both insert and supra‐aural earphones. The phones and probe tube were removed and replaced, and the RECD and REDD were remeasured. Results: RESPL was predicted using the RECD for insert earphone data and the REDD for supra‐aural earphone data. Reliability estimates were calculated as the difference between test and retest values for the RECD and REDD. Validity estimates were calculated as the difference between measured and predicted RESPL. Results indicate that the RECD and REDD have equal and high reliability and validity in predicting RESPL. Conclusions: It is concluded that the RECD and REDD may be used as level‐independent HL to SPL transforms as a substitute for in situ audiometric procedures.

A cross-over, double-blind comparison of the NAL-NL1 and the DSL v4.1 prescriptions for children with mild to moderately severe hearing loss

Abstract The relative effectiveness of the NAL-NL1 and the DSL4.1 prescriptions for 48 children with mild to moderately severe hearing loss was studied using a double-blind, four-period, two-treatment cross-over design in Australia and in Canada. Evaluations included speech perception tests, loudness ratings, reports from parents and teachers on functional performance in real life, childrens self-reports, paired-comparison judgements of intelligibility, and childrens preferences in real-world environments. Electroacoustic measures of hearing aids revealed that gain differences dominated the comparison. Across trials and measures, individual Australian children consistently preferred either the NAL-NL1 or the DSL v.4.1 prescription. An overall figure of merit (FOM), calculated by averaging the standardized difference scores between prescriptions for all measures, revealed that the strongest prescription-related differences were found in Australia. On average, an advantage and preference for the NAL-NL1 prescription was associated with lesser degrees of hearing loss. This research provides evidence on the effectiveness of the NAL-NL1 and DSL v.4.1 prescriptions, and highlights the need for evaluating and fine-tuning amplification to meet the diverse needs of individual children in real life. Sumario Se estudió la relativa efectividad de las prescripciones NAL-NL1 y DSL 4.1 en 48 niños con pérdidas auditivas de leves a moderadamente severas, usando un estudio doble ciego, en cuatro períodos y con un diseño cruzado de dos tratamientos en Australia y en Canadá. Las evaluaciones incluyeron pruebas de percepción de la palabra, tasas de reclutamiento, auto-reportes de los niños, juicios de inteligibilidad comparados por pares y preferencias de los niños en ambientes de mundo real. Las mediciones electroacústicas de los auxiliares auditivos revelaron que las diferencias en ganancia dominaron la comparación. En todas las pruebas y mediciones, los niños Australianos individualmente prefirieron de manera consistente tanto la prescripción NAL-NL1 como la DSL v.4.1. Una figura global de mérito (FOM), calculada al promediar las puntuaciones de diferencias estandarizadas entre prescripciones de todas las medidas, revelaron que las diferencias más fuertemente relacionadas con la prescripción, se encontraron en Australia. En promedio, la ventaja y preferencias hacia la prescripción NAL-NL1 se asoció con grados menores de pérdida auditiva. Esta investigación proporciona evidencia de la efectividad de las prescripciones NAL-NL1 y DSL v.4.1 y pone de relieve la necesidad de evaluar y de afinar la amplificación para alcanzar las diversas necesi-dades individuales de los niños en la vida real.