Distortion product otoacoustic emission level maps from normal and noise-damaged cochleae.

Distortion product otoacoustic emission (DPOAE) level mapping may be useful for detecting noise-induced hearing loss (NIHL) early. Employing DPOAE mapping effectively requires knowledge of the optimal mapping parameters to use for detecting noise-induced changes. The goal of this project was to show the map regions that differ most between normal and noise-damaged cochlea to determine the optimal mapping parameters for detecting NIHL. DPOAE level maps were generated for the 2f 1 -f 2 and the 2f 2 -f 1 DPOAEs for 17 normal hearing male subjects and 19 male subjects with NIHL. DPOAEs were measured in DPOAE frequency steps of approximately 44 Hz from 0.5 kHz to 6 kHz using constant f 2 /f 1 ratios incremented in 0.025 steps from 1.025 to 1.5 using both unequal-level (L1,L2 = 65,55 dB sound pressure level (SPL)) and equi-level (L1,L2 = 75,75 dB SPL) stimulus paradigms. Maximal responses for the 2f 2 -f 1 emission at L1,L2 = 65,55 dB SPL were found at lower ratios compared to previous studies. The map regions where NIHL eliminated or reduced DPOAE magnitude were identified. DPOAE level mapping using higher-level, equi-level primaries produced significantly more detectable emissions particularly for the 2f 2 -f 1 emission. The data from this study can be used to optimize DPOAE level mapping parameters for tracking noise-exposed subjects longitudinally.