Audiology and Speech Pathology - Theses
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ItemThe perception and production of prosody by adolescent users of cochlear implants( 2013)The development of the cochlear implant (CI) has provided access to speech for many people with profound hearing impairment. While access to coarse spectral information supports the perception of vowels and consonants, the temporal fine structure which supports an accurate perception of pitch is generally not perceived by CI users. In English, a stress-accent language, intonation is part of the prosodic system, and is realised through variations in pitch. For those profoundly deaf individuals who are implanted prelingually, the development of prosody is based solely on the input they receive from their device. In this study, the perception and production of prosody was investigated in a group of prelingually-deaf adolescent CI users, and compared to that of a normally-hearing (NH) control group. The CI users ranged in age from 12.1 – 21.5 years at the time of testing, with a mean age of implantation of 4.5 years, and a mean of 11.0 years experience listening with their CI. All used Nucleus devices and the Advanced Combinational Encoder (ACE) or SPeak processing strategies. The analysis of the perception and production of prosody by this group is of particular interest, as they form the first cohort of prelingually-deaf CI users who have now reached an age where their development of intonation should be mature, but who were implanted ‘early’ (for the time) at the Melbourne Cochlear Implant Clinic in Melbourne, Australia. Results of standard measures of speech perception and production indicated that the CI group members largely perceived vowels and consonants accurately with use of their CI, and produced acceptable phonetic variants of these sounds as well. The group also scored highly when discriminating between speech tokens with a stable fundamental frequency (F0) and those having a rising F0 of 11, 15 or 19 semitones (st). When discriminating between differences in rise onset and offset alignment which are typical of early- and late-aligned bitonal intonational pitch accents, the NH group could reliably discriminate differences in tonal alignment of 80 milliseconds. The CI group members performed inconsistently, with the results of only four users patterning in the same way as those of the NH listeners. The analysis of the production of prosody made use of an autosegmental metrical approach which combined phonetic and phonological considerations, and auditory and acoustic analyses. At a phrasal level, the CI users made more use of variations to phrasing to mark linguistic focus than the NH speakers did. The simultaneous control of durational cues at different levels of the prosodic hierarchy was a problem for the CI users, whose lengthening of the prosodic foot at the phrasal level reduced the cues to strong/weak syllables at the syllable level. Analyses indicated that many of the CI users produced either simple (H*) or bitonal pitch accents (L+H* and L*+H) on focused items, although some differences in fine phonetic detail were evidenced between the NH and CI groups’ productions. Overall, for the CI users, difficulties in the perception of pitch did not preclude the use of pitch accentuation to mark linguistic focus, but differences were seen between the CI users and the NH speakers in the fine timing of tones within pitch accents, and in the type and amount of pitch accents used.