CORTICAL AUDITORY-EVOKED POTENTIALS IN COCHLEAR IMPLANT PATIENTS

The current adjustment of coch lear implant (CI) speech processors is based on a knowledge of the lower and upper limits (T- and C-levels) f or electrical stimulus currents. These data are usually acquired from subjective classifications of individual patients. In cases with non-r eliable patient responses, objective methods are necessary. Especially for the estimation of correct T-levels, auditory evoked potentials (A EP) can be applied, since they allow the determination of response thr esholds in a frequency-specific manner. By determining the AEP of diff erent latencies, late cortical responses can be registered almost with out artifact contamination. These patients have been examined in 20 pa tients provided with 22- or 8-channel CI-systems (Nucleus(R) or Med-El (R) implants). In all cases, clear responses and clearly discernible t hreshold transitions could be detected. By making use of acoustical st imulation in a free sound field,subjective hearing threshold and the T -levels of electrical stimulation could be verified. Since late respon ses are generated in the primary auditory cortex, their assessment per mits a nearly integral functional control of the aided hearing system. To date, no problems have occured from maturation or attentional effe cts in either pediatric or adult patients. The applicability in very y oung children remains to be explored.