We propose to investigate effects of early hearing loss on binaural processing and high-frequency thresholds. Our Department attracts subjects with congenital aural atresia. These subjects have a malformed external and middle ear while the inner ear is usually normal. Successful surgery corrects large conductive hearing losses to normal or near normal limits. One set of experiments investigates the effects of hearing loss on different aspects of binaural processing. A battery of tests probes abilities to respond to interaural level, temporal, and phase differences. These tasks include binaural loudness, balances, interaural temporal difference limens, masking level differences, and freefield localizations. We hypothesize that many, but not all, of these abilities emerge rapidly after corrective surgery, showing that early conductive hearing loss does not necessarily lead to permanent impairment. A second and separate experiment investigates the cumulative effect of environmental noise. We propose to use hearing thresholds from protected and normal ears to measure relative contributions that genetic and environmental factors may have on long-term hearing loss. Data from a unique group of hearing-impaired listeners will be used to evaluate multiple effects of abnormal auditory experience. These subjects could yield significant answers to important questions in the study of auditory system development: particularly, the time course of recovery from altered inputs and the interaction of genetic and environmental influences.
