The behavior of acoustic distortion products in the ear canals of chinchillas with normal or damaged ears^a)

Acoustic intermodulation distortion products were measured in 15 ear canals of chinchillas with normal or damaged ears. Pretreatment results showed that when two primary tones at frequencies f_x and f₂f 1f2, were presented at levels from 30 to 90 dB SPL, acoustic distortion products at 2f1 f₂and 2f₂ f₁were 30 to 50 dB below primary-tone levels. Noise exposures that caused temporary or permanent hearing loss produced corresponding temporary or permanent reductions in distortion-product levels. Mechanical damage to the cochlea or middle ear reduced the distortion-product levels to below the noise floor of the measurement system. Comparisons of distortion-product level with behaviorally measured threshold shift and cochlear histopathology suggest that, in the absence of conductive impairment, the level of 2f₁ — f₂or 2f₂ — f₁can be used as a sensitive indicator of hearing sensitivity and the condition of the cochlea.