Auditory steady-state response evaluation of auditory thresholds in cochlear implant patients

The aims of this work were to characterize the electrophysiologic response obtained by measurement of the auditory steady-state response (ASSR) in patients with a cochlear implant (MXM Digisonic) and to study the relationship between the subjective thresholds of the implantees and those estimated using electrical auditory steady-state response (ASSR)-based objective audiometry. Five subjects were examined with the use of four carrier frequencies - 600, 1000, 2000 and 3500 Hz - modulated at frequencies between 70 and 85 Hz, a particular frequency of modulation being represented at a specific electrode (for each carrier frequency) as a particular pulse-width modulation frequency. The protocol consisted of testing Output and thresholds for different overall pulse durations for several stimulus (pulse) intensities, rendering multiple threshold measures (in duration) for each subject tested. The non-linearity of response growth, as a function of duration, provided the basis for teasing apart physioiogic response and electrical artefact in the supra-threshold recorded responses. Thresholds estimated with use of the electrical ASSR demonstrated reasonably good agreement with the subjective thresholds. The results obtained thus demonstrated the efficacy of the approach and are encouraging for further advances in cochlear implant applications.