This project aims to combine assessment of hearing abilities among subjects of different ages over time, together with information from their communication and health histories. Medical and cognitive data collected from subjects in the longitudinal study will be examined with respect to the audiologic and case history data. The two principal objectives of this project are: A) To study the contribution of medical, genetic, dietary and social factors to age-related auditory dysfunction; and B) To determine to what extent age, independent of other etiologic factors, causes a deterioration in hearing abilities. Measures of hearing assessment that continue to be collected include pure-tone hearing sensitivity, sentence understanding in noise, self-perceived hearing handicap, tympanometry, acoustic reflex thresholds, acoustic reflex magnitude, acoustic reflex adaptation, and acoustic reflex latency (the last five measures are part of the acoustic immittance battery of electrophysiologic tests). Age and gender specific reference ranges have been determined for hearing level and change in hearing level at 0.5, 1, 2, and 4 kHz. The resulting percentile curves represent norms for changes in hearing level and provide a reference for detecting when a person deviates from a normal pattern of change, thus helping in diagnosing problems with hearing or in monitoring hearing in occupational settings. These percentiles are the first reference curves that 1) provide standards for hearing level changes over periods of up to 15 years, 2) account for age differences in the distribution of hearing levels, and 3) are based on data from persons who have been systematically screened for otological disorders and evidence of noise induced hearing loss.
