Psychophysics of a peri-modiolar electrode array

Abstract

Psychophysical findings in three adult patients implanted with a CI22 cochlear prosthesis (Cochlear Limited) fitted with a developmental peri-modiolar electrode array have been reported. This array was moulded with a curvature approximating that of the inner wall of scala tympani but, after straightening and insertion into the cochlea, it adopted a position on average approximately half way between the inner and outer walls. However, the considerable variations in electrode trajectories across subjects allowed an analysis which could separate the effects due to longitudinal distance into the cochlea and lateral distance from the modiolus. Radiographic analysis enabled the positions of the individual electrodes to be measured, both longitudinally and laterally. This paper presents additional results and an in-depth analysis of the data, supported by psychophysical findings in subjects with straight arrays. It also introduces a model which describes the effect of distance from the modiolus on the loudness growth function.