Chirp-evoked auditory steady-state responses: Optimal parameters for rapid and objective tests of hearing

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Reliable methods for the assessment of hearing thresholds in quiet are of fundamental importance in audiology. For cooperative patients, the audiogram is measured in hearing tests whereas in non-cooperative patients such as in infants auditory evoked potentials (AEP) and otoacoustic emissions are used to assess the hearing ability. Especially auditory evoked potentials that were extracted from the electroencephalograms provide a robust and objective measure of threshold in quiet. For over 40 years, click-evoked auditory-brainstem responses (ABR) are used in clinical routine for the assessment of an average threshold in quiet over a wide range of frequencies but this stimulus type is not very useful when a frequency-specific estimate is required. An established approach is to use tone pulses instead of clicks but the responses to these stimuli are not robust enough for a clinical routine.Auditory steady state responses (ASSR) are a promising tool to overcome the above mentioned limitations. ASSR can be analysed in the spectral domain with powerful statistical tests. From a clinical perspective, it is useful that ASSR can be recorded for up to four frequencies and in both ears simultaneously. Commercial implementations were already successfully used in some clinics for the past few years. The limitation of this method is, so far, that the recordings are fairly time consuming. This may be overcome by an optimal choice of the stimuli and recording parameters. The aim of the present study is to investigate the impact of stimulus and recording parameters on ASSR for the clinically highly relevant stimulus type chirp in a multi-frequency setting. The chirp compensates for the delay of the traveling wave in the cochlea and thus produces large AEP response amplitudes. Although chirp-evoked ASSR are already used in the clinic, data on the influence of basic stimulus and recording parameters on chirp-evoked ASSR are not yet available. The multi-frequency chirp-evoked ASSR with optimised parameters may be the final step towards an objective assessment of frequency-specific thresholds in quiet in a clinic. The impact of stimulus and recording parameters is investigated in adult normal-hearing listeners and participants with a sensorineural hearing loss. These data are used as a basis for the optimisation of the parameters for a robust and efficient clinical ASSR recording.