Distortion product otoacoustic emissions in hearing-impaired mutant mice.

The acoustic intermodulation distortion product (2f1-f2) was recorded in the ear canal of two different types of normally hearing mice and in four different types of hearing-impaired mutant mice. In the normally hearing animals, primary tones at levels of 60- to 100-dB SPL evoked distortion product emissions (DP's) at 20-50 dB below the primary levels. In the hearing-impaired mutants the level was dependent on the particular type of auditory dysfunction associated with the mutation. In both the deafness and the viable dominant spotting mutants, where either the whole organ of Corti or the stria vascularis is affected by the mutation, no DP's could be detected. The quivering mutant has a central auditory dysfunction associated with the nuclei of the superior olivary complex and the lateral lemniscus, with apparently normal cochlear function. DP's at levels and thresholds similar to those in normally hearing animals were recorded in quivering mice. The Bronx Waltzer mutant has a full complement of outer hair cells but only about of 20%-25% inner hair cells. DP's of small amplitude were recorded but the thresholds were raised by about 30 dB. The data suggest that the 2f1-f2 emission can be used as a noninvasive monitor of cochlear function.