The Results in Patients Implanted with the Nucleus Double Array Cochlear Implant: Pitch Discrimination and Auditory Performance

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Abstract
In patients with total or surgically inaccessible cochlear obliteration, only a reduced number of active electrodes can be inserted with standard cochlear implants, resulting in below average auditory performance. Therefore, a special implant with two electrode arrays was developed on the basis of the Nucleus 22 cochlear implant, the socalled Double Array. One electrode array with 11 active electrodes is inserted into the basal turn of the cochlea, while the second array with 10 active electrodes is inserted into the second turn. The Double Array is now available on the basis of the more advanced Nucleus 24 with 11 active electrodes on each array and two reference electrodes, one at the case and the second one an additional ball electrode, which is placed under the temporalis muscle. For device description and surgical technique see Lenarz et al. (2001). This paper presents psychophysical data on pitch discrimination and auditory performance of patients implanted with a Double Array on the basis of the Nucleus 22. A prospective intra-individual study using a Latin square paradigm was performed in six adult patients with obliterated cochlea who received the Nucleus 22 Double Array. After appropriate fitting and loudness balancing, patients were tested either with the basal, the apical or both electrode arrays. Apart from auditory performance tests including numbers and monosyllable word tests, pitch discrimination was determined with a defined procedure. When activating each array alone, auditory performance was better with the basal array than with the apical array. Both arrays together showed marked improvement compared with the basal array, indicating an additional effect of the second array. Pitch discrimination was significantly better for the electrodes in the basal turn than in the second turn, indicating differences in electrical excitation of the auditory nerve fibers. Pitch discrimination was positively correlated with auditory performance data. The additional apical array leads to significant improvement in auditory performance in patients with obliterated cochleae by increasing the number of intracochlear electrodes. Despite reduced pitch discrimination, the apical array provides important information for speech recognition. For this reason the Double Array provides a profound advantage for patients with obliterated or surgically inaccessible cochleae.