Relationship between outer ear resonance and permanent noise-induced hearing loss.

INTRODUCTION: Prolonged exposure to noise produces permanent hearing loss in the frequency region centered around 4,000 Hz despite differences in the spectral and temporal characteristics of the noise. It is unclear to what extent properties of the auditory system contribute to the development of permanent hearing loss in this frequency region. This study was designed to evaluate the relationship between the frequency of peak outer ear resonance and the frequency of maximum hearing loss in a population of patients with a history of noise exposure. MATERIALS AND METHODS: Analysis of the frequency of maximum hearing loss was completed with sweep frequency Bekesy audiometry with resolution of 100 Hz. Peak outer ear resonant frequency was determined with a resolution of 175 Hz. RESULTS: The mean frequency of maximum hearing loss was 4,481 Hz whereas the mean peak outer ear resonant frequency was 2814 Hz for 43 ears. Pearson product correlation coefficient equaled .64 (P < .0001). CONCLUSIONS: Despite differences in the type and duration of noise exposure reported by the patients, the positive correlation between outer ear resonant frequency and frequency of maximum hearing loss emphasizes the role that external ear properties play in the development of the 4,000 Hz audiometric notch.

Perceived benefits of amplification as a function of central auditory status in the elderly.

A measure of perceived hearing aid benefit was obtained from 24 older hearing-impaired adults who had received their hearing aids a minimum of 6 months prior to this study. Subjects were also administered a battery of tests, including comparisons of maximum scores for phonetically balanced words and the Synthetic Sentence Identification Test to identify central auditory disorder. There appears to be no relationship between perceived hearing aid benefit and central auditory function as measured in this study. Several explanations for these somewhat surprising findings are offered, as well as clinical implications regarding the use of hearing aids by older adults.