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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Elisabeth Noordanus (Donders Institute for Brain, Cognition and Behaviour)
Lei Wang (Donders Institute for Brain, Cognition and Behaviour)
John van Opstal (Donders Institute for Brain, Cognition and Behaviour)

Abstract:
Auditory steady-state response (ASSR) is the sustained response on a periodic auditory stimulus, e.g., an amplitude-modulated sine. The modulation frequency(ies) of these tones can be measured using EEG. The clinical use of ASSR is the assessment of auditory function and hearing loss in newborns and young children. In this study, we used ASSR to explore nonlinearity in the human auditory system. Specific nonlinearities can putatively be used as the hallmark of function or dysfunction of a processing level in the auditory pathway (including the cochlea and the auditory nerve). Our main objective is to develop a reliable method to characterize the monaural and binaural auditory performance of hearing-impaired listeners, to be used for automatic fitting of hearing aids and cochlear implants. The secondary objective is to localize generators of significant ASSR associated with different nonlinearities of the auditory pathway. Methods: We performed two experiments to evaluate 2nd and 3rd-order nonlinearities of the auditory system. In both experiments (employing different frequency combinations) we presented stimuli as a superposition of four pure tones, two in the left and two in the right ear. The frequencies were chosen such that each interaction component between two or more sinuses would yield a unique frequency. Ten normal-hearing subjects were measured on two different days to check response repeatability. We used spectral analysis to identify frequencies with a significant response. Results: Major frequencies generated by 2nd (e.g., f2-f1) and 3rd-order (e.g., 2f2-f1) nonlinearities could be reliably detected in the EEG signals, which indicates that both 2nd and 3rd-order nonlinearities exist in the human auditory system. In general, the interactions between frequencies presented in the same ear were stronger than the interactions of frequencies across ears; moreover, 2nd-order responses were typically stronger than 3rd-order responses. The binaural response resulted to be larger when stimuli generated no 2nd-order monaural response. We also found that EEG electrodes above the temporal lobe and the central-frontal area yielded the highest signal-noise ratios. Finally, within-subject variability is smaller than between-subject variance. Conclusion: ASSR can be used to assess nonlinearities in the human auditory systems, both on a generic and an individual level.