[Effect of channel number decrease performance in two groups of implanted patients with Nucleus 22 and Med-el]

ABSTRACT

One of the main questions in the design of Cochlear Implants is "How many channels of stimulation are needed to achieve a high level, of speech understanding? Recently, some investigations have been carried out in which experiments were conducted with adults to provide an answer to this question. To reach 90% accuracy in quit. 5 channels are necessary for more difficult sentences produced by multiple talkers [Loizou et a1.1999] and 8 or more channels are necessary for monosyllabic rods [Dorman et al., in press]. In our research we extend our observations on the number of channels necessary to reach high levels of word Recognition Scores [Without Lip-reading]to a group of 30 implanted patients using the Nucleus 22 and Med-el[Combi 40+] cochlear implant devices, who had at least six months of Auditory Verbal Training experience following implant surgery. Simulating various numbers of channels was performed by reducing the number of active electrodes while the overall spectral band width was preserved. Five levels of active electrodes were simulated for nucleus devices, including 22, 16, 12.8 and 4 electrodes. Three levels of active electrodes were simulated for Med-El devices including 12, 8, and 4 electrodes. Word recognition score was measured on ten disyllabic words after each level. The results showed that word recognition scores decreased dramatically, as the number of electrodes was decreased from 12 to 8 and 4 electrodes [in nucleus devise] and from 8 to 4 electrodes [in med-el devices]. There was no significant difference in word recognition score as the number of electrodes was increased from 12 to 16 and 22 electrodes [in nucleus devices], and from 8 to 12 electrodes [in Med El devices]. Results indicate that if signal processors / electrode arrays could provide implanted patients with the equivalent of 8-1 2 functional channels of stimulation then the tasks of word recognition and language acquisition would be significantly facilitated