Biennial Symposium of the International Evoked Response Audiometry Study Group (IERASG) edition:XXI location:Windsor Barra Hotel, Rio de Janeiro, Brazil date:8–11 June 2009
Auditory steady-state responses (ASSRs) can be evoked by sinusoidally amplitude-modulated tones or by low frequency click trains. The purpose of this study was to confirm that ASSRs from cochlear implant (CI) users can be reliably evoked by electrical pulse trains with a pulse rate in the 40 Hz range. A measurement setup to facilitate recording with scalp electrodes was developed and it was determined to what extent objectively estimated hearing thresholds based on these responses can predict behaviorally obtained threshold levels.
Six CI users with a Nucleus implant were stimulated with pulse trains at rates from 35 to 44 Hz to characterize the influence of various stimulus parameters on the EASSRs. Either a pulse train on one electrode or simultaneous pulse trains on multiple electrodes have been used. To compensate for the influence of the artifacts introduced by the electrical stimulation and the RF transmission, artifact interpolation and artifact estimation were evaluated. To ensure the validity of the EASSRs, (1) on/off responses were recorded, (2) EASSR apparent latency across pulse rates was determined and (3) the amplitude growth of stimulus artifact and response amplitude were compared with each other.
The results demonstrate that EASSRs from CI users evoked by low rate pulse trains can be successfully separated from the artifacts of the electrical stimulation. Response amplitudes and latencies are comparable to the ones obtained in acoustically stimulated normal hearing patients. Hearing thresholds obtained from EASSR growth correlate well with behaviorally obtained threshold levels for CI users.