Longitudinal study of hearing aid effectiveness. I: Objective measures.

This report is the first of two detailing a longitudinal follow-up of hearing aid users. Sixty-five subjects were followed for 12 months post-hearing aid fitting. Objective tests included insertion gain, the Speech Perception in Noise (SPIN) test (Kalikow, Stevens & Elliot, 1977; Bilger, Neutzel, Rabinowitz, & Rzeczkowski, 1984) and the Nonsense Syllable Test (NST) (Levitt & Resnick, 1978) presented in quiet and noise backgrounds. Initially each subject's hearing aid was fit to the revised National Acoustic Laboratories prescriptive formula (NAL-R) (Byrne & Dillon, 1986) using insertion gain measures. Use gain, measured at 6 and 12 months post-fitting, indicated that subjects generally used those prescribed values, except for subjects in the steeply sloping configuration subgroup. The NST and SPIN tests were administered at the fitting and at 1, 3, 6, and 12 months post-fitting. No change in performance, or training effect, was found for the group or for factors of experience, degree of hearing loss, configuration of hearing loss, use time, or circuit type. Failure to demonstrate a training effect may be attributed, in part, to the fact that initial speech recognition testing was done with the hearing aid volume set at the prescribed values. None of the circuits used showed performance superiority, except when comparing scores for the NST obtained in a quiet background to those obtained in a background of speech-weighted noise. In that comparison, the users of adaptive filter circuits exhibited less deterioration of performance in a noise background.