Identification of speech by cochlear implant recipients with the multipeak(MPEAK) and spectral peak (SPEAK) speech coding strategies II. Consonants

Objective: The major objective of this study was to evaluate differences in consonant recognition with the Multipeak (MPEAK) and the Spectral Peak (SP EAK) speech coding strategies of the Nucleus-22 Cochlear Implant System, Th is objective was addressed by comparison of acoustic and electrode activati on analyses of consonants with cochlear implant recipients' responses to th ese same consonant tokens when they used the two speech coding strategies. Design: Nine subjects identified 14 English consonants with the MPEAK and S PEAK speech coding strategies, These strategies were compared with an ABAB design. Evaluation occurred during two weekly sessions after subjects used each strategy for at least 3 wk in everyday life. Results: Group medial consonant [aCa] identification scores with the SPEAK strategy were significantly higher than with the MPEAK strategy (76.2% vers us 67.5%; p < 0.001). This improvement was largely due to the significant i ncrease in information transmitted for the place feature (p < 0.001) throug h accurate tracking of second formant transitions and spectrally specific s timulation patterns to differentiate [s] from [integral] and [n] from [m], and the stop consonant bursts. For this reason, more nasal consonants were correctly identified with SPEAK, but there also were more non-nasal error r esponses when the nasal murmur was of unusually low amplitude. Consequently , significantly less information was transmitted for the nasality feature w ith SPEAK than MPEAK (p < 0.001). Conclusions: Electrical stimulation with the SPEAK strategy provided better spectral representation of the stop consonant bursts, tracking formant tra nsitions into the following vowel, frication in the consonant [integral], a nd the formants for the nasals [m] and [n] than with the MPEAK strategy. Th e marked improvement in recognition of the velar consonants, [g] and [k], w hich cannot be seen during speechreading, should allow greater ease and acc uracy of communication with SPEAK than MPEAK.