[Suppression tuning characteristics of the 2f1-f2 distortion product in cochlear microphonics and otoacoustic...

Suppression of the 2f1-f2 distortion product (DP) by the third tone was measured in cochlear microphonics (CM) and otoacoustic emissions (OAEs) in guinea pigs to clarify the generation site of the DPs. The DPs were elicited by the primary tones with frequencies of 4.62 kHz (f1) and 6 kHz (f2). Five dB-iso-suppression tuning curves (STCs) of the DPs were obtained by plotting the suppressor level as a function of its frequencies. The STCs in both CM DP and DPOAE had the shape of the letter "V" with the tip centering around the frequency of f2. The slopes of the STC on the higher frequency side were steeper than those on the lower side. As the intensity of the primary tones was decreased, the turning of the STC became sharper. These suppression properties indicate that the 2f1-f2 DPs were generated in the area on the basilar membrane where the characteristic frequency corresponded to those of primary tones, especially for the primaries at lower intensities. Because the suppression properties in CM DP and DPOAE were similar to each other, we concluded that these two phenomena had a common generation site.