One source for distortion product otoacoustic emissions generated by low- and high-level primaries

Abstract

Distortion product otoacoustic emissions (DPOAE) elicited by tones below 60-70 dB sound pressure level (SPL) are significantly more sensitive to cochlear insults. The vulnerable, low-level DPOAE have been associated with the postulated active cochlear process, whereas the relatively robust high-level DPOAE component has been attributed to the passive, nonlinear macromechanical properties of the cochlea. However, it is proposed that the differences in the vulnerability of DPOAEs to high and low SPLs is a natural consequence of the way the cochlea responds to high and low SPLs. An active process boosts the basilar membrane (BM) vibrations, which are attenuated when the active process is impaired. However, at high SPLs the contribution of the active process to BM vibration is small compared with the dominating passive mechanical properties of the BM. Consequently, reduction of active cochlear amplification will have greatest effect on BM vibrations and DPOAEs at low SPLs. To distinguish between the "two sources" and the "single source" hypotheses we analyzed the level dependence of the notch and corresponding phase discontinuity in plots of DPOAE magnitude and phase as functions of the level of the primaries. In experiments where furosemide was used to reduce cochlear amplification, an upward shift of the notch supports the conclusion that both the low- and high-level DPOAEs are generated by a single source, namely a nonlinear amplifier with saturating I/O characteristic.

The Role of BKCa Channels in Electrical Signal Encoding in the Mammalian Auditory Periphery

“…Our present data confirm a modest degree of cochlear dysfunction evident in the DPOAE, which is consistent with OHC dysfunction (Liberman et al, 2002;Lukashkin et al, 2002). However, sharp mechanical frequency tuning critically requires the amplification process provided by OHCs (Kiang et al, 1970;Dallos and Harris, 1978).…”

Influence of Ketamine–Xylazine Anaesthesia on Cubic and Quadratic High-Frequency Distortion-Product Otoacoustic Emissions

“…Lukashkin et al 2002;Mills and Rubel 1994). However, in our case, phase data were quite variable and did not allow a consistent interpretation.…”

“…This is exceptional since in other mammals studied, the generation of the f2-f1 emission usually requires higher stimulus levels (e.g. Kujawa et al 1995;Frank and Kössl 1996;Lukashkin et al 2002;Wittekindt et al 2009). The fact that in the present study the stimulus frequency ratio was optimised for the f2-f1 distortion before the respective measurements may have contributed to this sensitivity.…”

Temperature dependence of distortion-product otoacoustic emissions in tympanal organs of locusts

“…Lukashkin et al, 2002) and in insects (e.g. Kössl et al, 2007) was found to be physiologically much more vulnerable than the high-level component, which could lead to the suggestion of two L2-level-dependent mechanisms for DPOAE generation.…”

“…Kössl et al, 2007) was found to be physiologically much more vulnerable than the high-level component, which could lead to the suggestion of two L2-level-dependent mechanisms for DPOAE generation. For mammals, Lukashkin et al (Lukashkin et al, 2002), however, provided evidence that both components are evoked by a single source, a non-linear amplifier with saturating input/output characteristics. Mammalian cochlear amplification of basilar membrane vibration is largest at low levels (Dallos and Fakler, 2002), and the impact of active amplification on the basilar membrane vibration reaches saturation if the input levels are increased beyond ~40-60dBSPL.…”