A comparison of three speech coding strategies using an acoustic model of a cochlear implant

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Abstract
Three alternative speech coding strategies suitable for use with cochlear implants were compared in a study of 3 normally hearing subjects using an acoustic model of a multiple-channel cochlear implant. The first strategy (F2) presented the amplitude envelope of the speech and the 2nd formant frequency. The 2nd strategy (F0 F2) included the voice fundamental frequency, and the 3rd strategy (F0 F1 F2) presented the 1st formant frequency as well. Discourse level testing with the speech tracking method showed a clear superiority of the F0 F1 F2 strategy when the auditory information was used to supplement lipreading. Tracking rates averaged over 3 subjects for nine 10 min sessions were 40 wpm [words per min] for F2, 52 wpm for F0 F2, and 66 wpm for F0 F1 F2. Vowel and consonant confusion studies and a test of prosodic information were carried out with auditory information only. The vowel test showed a significant difference between the strategies, but no differences were found for the other tests. Apparently, the amplitude and duration cues common to all three strategies accounted for the levels of consonant and prosodic information received by the subjects, while the different tracking rates were a consequence of the better vowel recognition and the more natural quality of the F0 F1 F2 strategy.

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