Estimation of Auditory Thresholds in Cochlear Implant Subjects Using ASSR

Abstract

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 and to study the relationship between the subjective thresholds of the implantees and those estimated using acoustical auditory steady-state response -based objective audiometry. Nine subjects were examined with the use of four carrier frequencies--500, 1000, 2000 and 4000 Hz-- modulated at frequencies between 78 and 95 Hz. Free field behavioral threshold estimation was carried out using standard test protocols. The results revealed that there was a good correlation between the acoustical ASSR and behavioral thresholds. In addition there was no statistical difference between the two data, suggesting acceptable accuracy of behavioral threshold estimation with the use of ASSR. Thus, ASSR technique shows great promise as a way to assess auditory sensitivity in subjects with cochlear implants who cannot reliably respond on behavioral testing. The results of the present study also suggests need for an in depth investigation into efficacy of some measurement of supra threshold processes which would be much more helpful in terms of monitoring device performance and adjust mapping. Finally the results need to be confirmed in a greater number of subjects, not only for further validation of the method, but also to acquire sufficient data to support the development of an expert system, allowing the automated assessment of cochlear implantees and the programming of these processors. The present study highlights the potential implications of ASSR instead of behavioral methods in fitting of young children and other difficult-to-test to test patients.