Evidence for the influence of aging on distortion-product otoacoustic emissions in humans.

Previous measures of distortion-product otoacoustic emissions (DPOAEs) in young adults suggested that these responses were capable of detecting the functional effects of auditory aging. The primary goal of the present study was to provide more detailed evidence for the influence of aging processes on the ability of healthy, older ears to generate DPOAEs. Toward this end, DPOAEs were examined in a series of human subjects, with clinically normal hearing, ranging in age from 31 to 60 years. Acoustic-distortion products were measured in two basic forms consisting of "audiograms" and response/growth or input/output functions. Distortion-product "audiograms" depicted the detailed frequency pattern of DPOAE amplitudes in response to constant-level stimuli, whereas the growth functions described the detection "threshold" and suprathreshold aspects of DPOAE activity, at specific frequencies, in response to primary tones that were systematically increased in level. The principal finding was that, when compared to emissions in young ears, DPOAEs accurately tracked the systematic deterioration of high-frequency hearing in aging individuals.