Age-related changes in evoked otoacoustic emission in normal-hearing ears.

The evoked otoacoustic emissions (e-OAEs) elicited by both tone-bursts and clicks were investigated in normal-hearing ears of three age groups: young age group (approximately 30 years), middle age group (31-50 years) and old age group (51 years approximately). The pseudothreshold of tone-burst e-OAE at stimulus frequencies between 500 Hz and 2 kHz was significantly elevated in the middle and old age groups compared with that in the young age group. When the relationship between averaged emission cochleograms drawn from the mean pseudothresholds of tone-burst e-OAEs at 6 stimulus frequencies between 500 Hz and 4 kHz and averaged pure-tone audiograms was analyzed, a clear difference was found among the three age groups in a frequency range between 500 Hz and 2 kHz. Total echo power, reproducibility, highest peak power and frequency area peak power up to 4 kHz in click e-OAE significantly decreased in the middle and old age groups compared with those in the young age group. These results indicate the possibility that the function of cochlear micromechanics deteriorates in all cochlear partitions with increasing age, even in normal-hearing ears.