Group correlations between decline in the outer hair cell system and overall auditory sensitivity start to occur in middle age. A) Correlations between ABR thresholds and DPOAE level shifts are significant, only at the higher frequencies (30–50 kHz) in middle age: F(1,124) = 5.32, P = 0.0228, r2 = 0.0411. B) The correlations in the high frequency range become much stronger in old age: F (1,84) =15.21, P = 0.0002, r2 = 0.1533. Here, and in the remaining figures, dashed lines in the regression plots represent 95% confidence intervals.
Abbreviations: ABR, auditory brainstem response; DPOAE, distortion-product otoacoustic emission.