Measurement of medial olivocochlear efferent activity in humans: comparison of different distortion product otoacoustic emission-based paradigms.

OBJECTIVE

To assess the suitability of contralateral suppression (CS) of distortion product otoacoustic emissions (DPOAEs) for measurement of activity of the medial olivocochlear (MOC) efferents.

BACKGROUND

The MOC efferent system has been shown to be involved in sound discrimination, selective attention to tones, sound localization, and protection of the cochlea against noise. A great variety of paradigms for measurement of MOC activity by CS of OAE (MOC reflex [MOCR]), has been described. An issue of this approach is the dependence of the CS values on stimulus parameters, especially when DPOAE are used.

METHODS

Four different measurement paradigms, which used different combinations of stimulus frequencies and primary tone levels, were applied in 16 human subjects.

RESULTS

Mean absolute values of CS were in the range of 1.2 to 2.6 dB. The use of different stimulus parameters produced not only MOCR values of different size-which was expected-but, in many cases, also different relative classifications of the subjects according to their MOCR strength.

CONCLUSION

The suppression effects on DPOAE demonstrated in this study reflect MOC activity. However, the new conclusion from our data is that CS of DPOAE measurements, as they were used in this study, may not allow for a consistent quantitative classification of human subjects according to their MOCR strength. This finding concerns interpretation of previous studies using CS of DPOAE and analogous future studies. One future approach may lie in the separation of the DPOAE components to distinguish interference phenomena, which complicate interpretation of CS values.