Auditory distortion products measured with averaged auditory evoked potentials.

The purpose of this investigation was to describe the properties of averaged auditory evoked potential distortion products (AEP-DPs) in guinea pigs. This study provided a step toward developing a clinical index of nonlinear processing of auditory signals and supplied a baseline for studies evaluating the effect of cochlear damage on AEP-DPs. The amplitude of the AEP-DPs was evaluated as a function of f2/f1 ratio (1.12-1.52) and primary frequency (500 Hz-2000 Hz). The amplitude of the AEP cubic difference tone (AEP-CDT) increased with increasing f2/f1 ratio for the 500-Hz f1 primary and remained constant for the 800-Hz and 1700-Hz f1 primaries. The AEP-CDT generated by the 1100-Hz and 1400-Hz f1 primaries was maximum for the middle f2/f1 ratios (1.22, 1.32, and 1.42). The AEP-CDT could not be distinguished from the noise floor for the 2000-Hz f1 primary. The AEP difference tone (AEP-DT) was larger and more frequently identified than the AEP-CDT. The amplitude of the AEP-DT decreased with an increase in f2/f1 ratio. The decrease was more pronounced for low-frequency f1 primaries than for high-frequency f1 primaries.