Distortion-product otoacoustic emissions measured at high frequencies in humans.

Distortion-product otoacoustic emissions (DPOAEs) elicited with stimulus frequencies less than or equal to 8 kHz have been used in hearing clinics to assess whether the middle ear and cochlea are normal, but high-frequency hearing (>4 kHz) is most vulnerable to cochlear pathology. It might prove useful to measure DPOAEs with even higher frequency stimuli (>8 kHz), but there have been few reports of such studies in humans. DPOAEs have been measured in other mammals to the upper range of hearing sensitivity. The purpose of this study was to compare some characteristics of DPOAEs in human subjects elicited with high-frequency stimuli with those that have been extensively measured with lower-frequency stimuli. The primary goal was to establish if the same phenomenon responsible for the behavior of low-frequency DPOAEs is responsible for the behavior of high-frequency DPOAEs. Specifically, the DPOAE level with stimuli varied from 2 to 20 kHz, growth functions of DPOAEs, effects of varying the primary frequency ratio (f2/f1) on the DPOAE level, and DPOAE group delay were determined. Because the behaviors appeared to vary smoothly with stimulus frequency, the study suggests that emissions measured from 2 to 20 kHz were the product of the same biological process.