No abstract

In 1994, Moodie, Seewald, & Sinclair described the development of a clinical procedure for predicting real-ear hearing instrument performance in young children. The purpose of the present study was to determine the validity of this procedure for predicting the real-ear aided gain (REAG) and real-ear saturation response (RESR) of hearing instruments worn by children. To this end, both the REAG and RESR were measured, through probe-microphone measures, and predicted, using the Moodie et al. procedure. The findings confirmed that the 2-cc coupler-based procedure, with individualized acoustic transforms, described by Moodie et al., resulted in highly accurate predictions of real-ear hearing instrument performance for both REAG and RESR at five test frequencies. The implications of these findings for the clinical fitting of hearing instruments in infants and young children are discussed.

For a given individual, the applicability of an average real-ear-to-coupler transfer function in the fitting of hearing aids is of limited utility, because the acoustical properties of individual ears may differ substantially from average transformation values (Feigin, Kopun, Stelmachowicz, & Gorga, 1989; Fikret-Pasa & Revit, 1992). It has been suggested, therefore, that individual real-ear-to-coupler difference (RECD) measures should be obtained whenever possible and applied within the fitting process (Hawkins, 1992; Nelson Barlow, Auslander, Rines, & Stelmachowicz, 1988). The purpose of this study was to investigate the repeatability of a specific RECD measurement procedure that has been developed for clinical application with young children (Moodie, Seewald, & Sinclair, 1994). The test-retest reliability of this procedure is reported for 10 adults and 90 children in the birth-to-7-year age range.

The predicted real-ear-to-coupler difference (RECD) values currently used in pediatric hearing instrument prescription methods are based on 12-month age range categories and were derived from measures using standard acoustic immittance probe tips. Consequently, the purpose of this study was to develop normative RECD predicted values for foam/acoustic immittance tips and custom earmolds across the age continuum. To this end, RECD data were collected on 392 infants and children (141 with acoustic immittance tips, 251 with earmolds) to develop normative regression equations for use in deriving continuous age predictions of RECDs for foam/acoustic immittance tips and earmolds. Owing to the substantial between-subject variability observed in the data, the predictive equations of RECDs by age (in months) resulted in only gross estimates of RECD values (i.e., within ± 4.4 dB for 95% of acoustic immittance tip measures; within ± 5.4 dB in 95% of measures with custom ear molds) across frequency. Thus, it is concluded that the estimates derived from this study should not be used to replace the more precise individual RECD measurements. Relative to previously available normative RECD values for infants and young children, however, the estimates derived through this study provide somewhat more accurate predicted values for use under those circumstances for which individual RECD measurements cannot be made.

The foam tip to earmold correction values developed in this study can be used to provide improved estimations of earmold RECDs. This may support better accuracy in acoustic transforms related to transforming thresholds and/or hearing aid coupler responses to ear canal sound pressure level for the purposes of fitting behind-the-ear hearing aids.