Simultaneous Measurement of Peripheral Compres- Sion Using Oaes and Assr

Objective assessment of auditory function is an important topic in research and clinical practice. Particularly, assessment of the compressive nonlinearity provides useful information about the inner ear. One way to assess auditory processing is the measurement of the neural response elicited by acoustic stimulation via electroencephalography (EEG). Specifically, auditory-steady state responses (ASSR) receive increasing attention due to their ease of measurement and reproducibility. ASSRs have recently been used to estimate the state of the compressive nonlinearity in the peripheral auditory system. Since it is commonly assumed, that outer hair cells in the inner ear play an important role in the compressive nonlinearity, is it desirable to selectively obtain information about the inner ear, rather than the system as a whole. The common method to objectively measure inner ear activity is the measurement of distortion-product otoacoustic emissions (DPOAEs) via acoustical signals in the ear canal. The nonlinear nature of generation of the DPOAE however, complicates the interpretation of the results, especially on an individual basis. In the current study, the signal in the ear canal, present during ASSR measurements is utilized to extract sinusoidally-amplitude modulated OAEs (SAMOAEs). The hypothesis is, that the stimulus used to evoke ASSRs will cause acoustic energy to be reflected back from the inner ear into the ear canal, where it can be picked up as an OAE. This signal can provide information about a) the state of cochlear processing, and b) the contribution of cochlear compression to the compression obtained by ASSRs. Results indicate, that SAMOAEs can be extracted while measuring ASSRs using sinusoidally-amplitude modulated tones, with characteristics similar to those of stimulusfrequency otoacoustic emissions, SFOAE. A robust extraction and evaluation of SAMOAE in connection with ASSR provides additional information about the state of the peripheral auditory system without the need of additional measurement time.