The DPOAE-gram sreveal significant differences between the old subjects and the other two age groups. A) DPOAE levels were similar between the young adults and middle-aged mice, but large declines occurred in old age. Note the larger error bars in the oldest group. B) DPOAE level shifts compared with young adult: the middle-aged subjects showed a 2–5 dB change in the middle and high frequencies of the mouse hearing range, but there were large 10–25 dB shifts for the old group.
Abbreviations: DP, distortion product; DPOAE, distortion-product otoacoustic emission; NF, noise floor.