Coding of voice source information in the Nucleus cochlear implant system

Abstract

Two studies are reported in which the effectiveness of explicitly coding voicing and fundamental frequency information for the Nucleus cochlear implant was investigated. ln the first study, the voicing perception of a group of three experienced Multipeak users was evaluated when they were using Multipeak and a modified Multipeak in which the explicit fundamental frequency and voicing cues were eliminated and replaced with a 250-Hz constant rate of stimulation. The results of consonant and monosyllabic word tests showed that there was no significant difference in the subjects' ability to discriminate voicing. In the second study, the ability of a group of five experienced users of the constant rate spectral maxima sound processor (SMSP) strategy to discriminate suprasegmental contrasts was evaluated when they were using the SMSP strategy and a modified SMSP strategy that included a rate-encoded representation of the fundamental frequency on the most apical stimulation channel. The results of intonation, roving stress, and question-statement tests showed that there was no significant difference between the scores recorded with these strategies. Since the temporal voicing cue is not a primary cue to voicing discrimination for Multipeak users, and the provision of an additional rate cue to the SMSP strategy does not improve SMSP users' ability to discriminate suprasegmental contrasts, the results of these studies indicate that in the cases investigated, the coding of voice source information by rate of stimulation does not significantly augment the cues present in the spatially distributed constant rate stimulation pattern.