Electrically Elicited Stapedius Reflex and Preferred Listening Level in a Patient with a Cochlear Implant

Abstract

In a patient with a multichannel cochlear implant, it was possible to demonstrate stapedial reflex contraction to intracochlear electrical stimulation. Using a standard immittance measurement technique, characteristics of the electrically evoked reflex were compared to analogous characteristics of the acoustically evoked reflex. Latency-intensity functions were similar for the two modes of excitation, but reflex waveform morphology and amplitude growth functions were different. The effects of electrode position and electrode spacing were of particular interest. In our patient, neither position nor spacing affected onset latency. Both electrode position and electrode spacing did, however, affect reflex amplitude. As position moved from base to apex, reflex amplitude increased systematically and substantially. Although we have reported amplitude results in suprathreshold current level, we also found the same relationship across electrode position for stimulation at constant current level. Reflex amplitude by electrode spacing was also affected. The widest spacing (3 mm) produced the largest reflex amplitude, and the narrowest spacing (1.5 mm) produced the smallest amplitude. The spacing effect, however, showed a strong interaction with electrode position, being greatest at the apical position and least at the basal position.