The effects of limiting the number of Nucleus 22 cochlear implant electrodes programmed on speech perception

The purpose of this double-blind study was to evaluate systematically the effects of varying programmed electrodes on speech perception. The performance of five subjects implanted with the Nucleus 22-electrode cochlear implant was compared on the Four-Choice Spondee test, the Central Institute for the Deaf Sentence test, and Speech Tracking across the following conditions: (1) five most apical electrodes eliminated from the subject's MAP (stimulus parameters); (2) five most basal electrodes eliminated from subject's MAP; (3) the middle five electrodes eliminated from subject's MAP; and (4) subject's current MAP. Statistically significant differences were found for the Four-Choice Spondee test and both the auditory-only and auditory-plus-lipreading Speech Tracking measures. Three subjects demonstrated poorer performance on all test measures when the five electrodes from the apical portion of the array were not programmed. Two subjects performed equally well, regardless of MAP condition. Group means for all test measures present a trend of consistently poorer performance when the -5 Apex MAPs were utilized. A subjective rating scale was consistent with the perceptual tests, with all subjects best liking their current MAP and least liking the -5 Apex MAP. Results suggest that for some subjects, a fixed place code may control their ability to use spectral information for speech discrimination. For these subjects, first formant information (F1) traditionally coded on the most apical electrodes could not be utilized as effectively when coded on the adjacent middle electrodes.