Deep Electrode Insertion in Cochlear Implants: Apical Morphology, Electrodes and Speech Perception Results

Ingeborg Hochmair[1], Wolfgang Arnold[2],

Peter Nopp[1], Claude Jolly[1], Joachim Müller[3] and Peter Roland[4]

[1] MED-EL Medical Electronics - Innsbruck, Austria, [2] HNO- Universitätsklinik, Klinikum Rechts der Isar, Munich, Germany, [3] Klinik und Poliklinik für HNO Kranke, Julius-Maximilians-Universität, Würzburg, Germany and [4] Department of Otolaryngology, University of Texas, Dallas, Texas, USA

Results:

Test results in a study conducted with 10 MED-EL subjects implanted with a fully inserted standard electrode array (31 mm), indicate advantages of an electrode configuration that provides a wide distribution of channels over the entire length of the cochlea. Subjects were tested in 4 conditions: only the 8 most basal channels activated (basal 8), an uneven distribution of 8 channels over the full length of the cochlea (spread 8a and 8b)and with all 12 channels active. Subjects were post-lingually deaf adults, evaluated with monosyllabic word, and a sentence test used to determine the speech reception threshold. The spread 8 conditions, which provides stimulation over the entire length of the cochlea, yielded an average improvement of 24% in monosyllabic words score, compared to the basal 8 condition Speech reception thresholds decreased significantly in the spread 8 condition compared to the basal 8 condition, where only a restricted region of the cochlea was stimulated. (Hochmair, 2003)

Similar findings were shown in a study of eight MED-EL implant users. The investigators assessed the effects of electrode insertion depth and contact separation on speech discrimination. The results showed that, for six active channels, speech perception was significantly higher with the channels distributed over almost the entire length of the array (spread 6) when compared with the channels concentrated near to the basal end of the array (partial 6). (Nahler, 2005)

There are two possible reasons why speech discrimination improves and speech thresholds are lower when stimulating the entire cochlea. Complete cochlear coverage allows a more natural frequency to place match, meaning that the physical location of the electrode contacts more closely matches the natural tonotopicity of the cochlea. A second possible reason is that a longer electrode array allows wider contact spacing, thus reducing channel interaction. From these studies and others, we see that complete cochlear stimulation has clear advantages in speech performance for cochlear implant users.

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