Identification of Speech by Cochlear Implant Recipients with the Multipeak (MPEAK) and Spectral Peak (SPEAK) Speech Coding Strategies I. Vowels

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Abstract
The main objective was to evaluate differences in performance associated with the two speech coding strategies. To achieve this objective, acoustic and electrical analyses of vowels identified by cochlear implant recipients were compared with their responses when they used the Multipeak (MPEAK) and the Spectral Peak (SPEAK) speech coding strategies of the Nucleus Cochlear Implant System. Nine subjects identified pure and r-colored English vowels with the two speech coding strategies. The two processing strategies were compared using an ABAB design. Evaluations were conducted at two weekly sessions after at least 3 wk of use with each strategy. Group vowel identification scores with the MPEAK versus the SPEAK strategy were not significantly different (72.3% and 73.4%, respectively). However, hierarchical loglinear analysis of group data showed that transmitted information of r-color, duration, and second-formant features was significantly better with the SPEAK than with the MPEAK strategy. In contrast, identification of the first formant feature was significantly better with the MPEAK than with the SPEAK strategy. Individual subjects had different error patterns in response to the 14 vowels. Electrical stimulation with the SPEAK strategy provides clearer spectral representation of second formant and duration information as well as second and third formant change in r-colored vowels than with the MPEAK strategy. Consequently, there was marked improvement in recognition of r-colored vowels with SPEAK compared with MPEAK. In contrast, transmitted information for first-formant features was significantly less with SPEAK than with MPEAK. This may have occurred because four instead of six to eight electrodes were assigned to first formant frequencies with SPEAK versus MPEAK.