Graeme Clark Collection
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ItemPitch and vowel perception in cochlear implant users( 1994)Two methods of determining the pitch or timbre of electrical stimuli in comparison with acoustic stimuli are described. In the first experiment, the pitch of pure tones and electrical stimuli were compared directly by implant users who have residual hearing in the non-implanted ear. This resulted in a relationship between frequency in the non-implanted ear and position of the best-matched electrode in the implanted ear. In the second experiment, one- and two-formant synthetic vowels, with formant frequencies covering the range from 200 to 4000 Hz, were presented to the same implant users through their implant or through their hearing aid. The listeners categorised each stimulus according to the closest vowel from a set of eleven possibilities, and a vowel centre was calculated for each response category for each ear. Assuming that stimuli at the vowel centres in each ear sound alike, a second relationship between frequency and electrode position was derived. Both experiments showed that electrically-evoked pitch is much lower than that produced by pure tones at the corresponding cochlear location in normally-hearing listeners. This helps to explain why cochlear implants with electrode arrays that rarely extend beyond the basal turn of the cochlea have achieved high levels of speech recognition in postlinguistically deafened adults without major retraining or adaptation by the users. The techniques described also have potential for optimising speech recognition for individual implant users.
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ItemUsing an automatic word-tagger to analyse the spoken language of children with impaired hearing( 1994)The grammatical analysis and description of spoken language of children with impaired hearing is time-consuming, but has important implications for their habilitation and educational management. Word-tagging programs have achieved high levels of accuracy with text and adult spoken language. This paper investigates the accuracy of one automatic word tagger (AUTASYS 3.0 developed for the International Corpus of English project, ICE) on a small corpus of spoken language samples from children using a cochlear implant. The accuracy of the tagging and the usefulness of the results in comparison with more conventional analyses are discussed.
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ItemCombination and comparison of electric stimulation and residual hearing( 1994)Speech processing for cochlear implant users has now reached a level where some severely hearing-impaired hearing aid users may be better aided by a cochlear implant, or a hearing aid and implant together. This paper reviews studies comparing the loudness, pitch, and vowel perception in opposite ears of adults using cochlear implants and hearing aids. A study of nine subjects showed narrow dynamic ranges and steep loudness growth in both ears. Mismatches in aided thresholds and dynamic ranges at different frequencies resulted in highly variable loudness differences between the ears for some subjects. A comparison using pure tones showed that the electric pitch depended on both rate and electrode site. Pitch of electrodes was lower than expected from the characteristic frequency distribution in a normal cochlea. Synthetic vowels were used to show that signals presented via the implant and hearing aid may be perceived as different vowels in the two ears.
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ItemHabilitation issues in the management of children using the cochlear multiple-channel cochlear prosthesis( 1993)Since 1985, a significant proportion of patients seen In the Melbourne cochlear Implant clinic have been children. The children represent a diverse population, with both congenital and acquired hearing-impairment, a wide-range or hearing levels pre-Implant, and an age range from 2 years to 18 years. The habilitation programme developed for the overall group must be flexible enough to be tailored to the Individual needs of each child, and to adapt to the changing needs or children as they progress. Long-term data shows that children are continuing to show Improvements after 5-7 years of device use, particularly In their perception of open-set words and sentences. Habilitation programs must therefore be geared to the long-term needs of children and their families. Both speech perception and speech production need to be addressed In the specific content of the habilitation program for any Individual child. In addition, for young children, the benefits or Improved speech perception should have an Impact on development of speech and language, and the focus of the programme for this age child will reflect this difference In emphasis. Specific materials and approaches will vary for very young children, school-age and teenage children. In addition, educational selling will have a bearing on the Integration of listening and device use Into the classroom environment.