Distortion-product otoacoustic emission suppression growth in normal and noise-exposed rabbits

This study investigated noise-induced changes in suppression growth (SG) of distortion product otoacoustic emissions (DPOAEs). Detailed measurements of SG were obtained in rabbits as a function of f2 frequencies at four primary-tone levels. SG measures were produced by using suppressor tones (STs) presented at two fixed distances from f2. The magnitude of suppression was calculated for each ST level and depicted as contour plots showing the amount of suppression as a function of the f2 frequency. At each f2, SG indices included slope, suppression threshold, and an estimate of the tip-to-tail value. All suppression measures were obtained before and after producing a cochlear dysfunction using a monaural exposure to a 2-h, 110-dB SPL octave-band noise centered at 2 kHz. The noise exposure produced varying amounts of cochlear damage as revealed by changes in DP-grams and auditory brainstem responses. However, average measures of SG slopes, suppression thresholds, and tip-to-tail values failed to mirror the mean DP-gram loss patterns. When suppression-based parameters were correlated with the amount of DPOAE loss, small but significant correlations were observed for some measures. Overall, the findings suggest that measures derived from DPOAE SG are limited in their ability to detect noise-induced cochlear damage.