Speech coding strategies of the digisonic fully digitized cochlear implant.

The Digisonic is a fully digitized cochlear implant. Because of its articulated array, its 15 electrodes can be inserted in the cochlea. Each electrode is recessed in a special silastic compartment of the array and has a very large stimulation area thanks to its large microrelief surface area. The small volume of its implanted receiver (flat cylinder diam 29 mm, 6.9 mm thick) allows it to be placed in 2-year-old children. The 128 point FFT of this device supply the patient with a full set of sound information between 64 and 7800 Hz. Electrode stimulation mode is sequential and stimulation rhythm is programmable. Electric crosstalk is decreased by the shape of the electrode array, and optionally by special programming of the neighboring electrodes. The speech therapist may select the width and peak value of each frequency band handled by each functional electrode. Because the versatility of this digitized emitter, many speech coding strategies can be easily programmed as a function of electrode responses or particular scientific considerations. A special version of this device, consisting of 10 separate electrodes, has been designed for use in patients with total obstruction of the cochlea. These insulated wires may be inserted one by one in the inner ear in 10 different recesses gently drilled in the bony cochlea. This device was placed in 46 patients between 1992 and 1994, including 8 young children (aged 2-9 years, mean 5 years) and 9 patients with total cochlear obstruction.