Graeme Clark Collection
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ItemSpeech perception outcomes for older patients using the nucleus cochlear implant [Abstract]( 2002)With improved medical technology and increased life expectancy, more patients are receiving cochlear implants at a later age. It is important to examine speech perception outcomes for older patients, in order to be able to provide appropriate pre-operative counselling regarding post-operative expectations. Speech perception scores for patients at the Melbourne Cochlear Implant Clinic implanted at age 65 or more were examined, and compared to the adult population implanted under the age of 65. (All of these patients were users of SPEAK or later strategies.) The aims were to see if speech perception scores were significantly different between the two groups as a whole, and to see if a correlation existed between increasing age of implantation above 65 and speech perception scores. Preliminary results suggest that there is a small but significant effect of age on speech perception outcomes. The findings from this study will be used to help clinicians provide more accurate advice and counselling for older patients, regarding the potential outcomes from a cochlear implant.
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ItemFactors affecting speech perception outcomes for older children using multichannel cochlear implants( 2002)Experience with cochlear implantation in early-deafened teenagers or young adults has been somewhat disappointing, however, in recent years a proportion of older children have demonstrated excellent speech perception performance. There appears to be a wide gap between the good and poor performers within this group. It is important to investigate the possible factors influencing performance so that adolescents and their families are able to make informed decisions regarding cochlear implant surgery. This study considered a number of factors in a group of 25 children implanted in Melbourne between the ages of 8 and 18 years. Each subject completed open set speech perception testing using BKB sentences before and after implantation and pre-operative language testing using the Peabody Picture Vocabulary Test. Data were collected regarding the type of hearing loss, age at implant, age at hearing aid fitting, audiometric details, and the pre-and postoperative communication mode. Multivariate analysis suggested that three factors have a significant predictive value for post-implant speech perception: pre-operative open-set sentence score, duration of profound hearing loss and equivalent language age. These three factors accounted for 66% of the variance in this group. The results of this study suggest that children who have useful pre-implant speech perception, and higher age-equivalent scores on language measures, would be expected to do well with a cochlear implant. A shorter duration of profound hearing loss is also advantageous. Mean speech perception scores for the older group were not significantly different from younger children.
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ItemInhibition underlies the encoding of short voice onset times in the ventral cochlear nucleus( 2001)Recent experiments in our laboratory have shown that voice onset time (VOT), the time between consonant release and the first glottal pulse of an ensuing vowel, is effectively encoded by neurons within the ventral cochlear nucleus (VCN). In this investigation we examined the possible neural mechanisms which may underlie this VOT encoding. In male rats anaesthetised with urethane (2.5g1kg i.p), microelectrodes containing 1M potassium acetate, were inserted into the VCN. Speech stimuli consisting of 3 syllables spoken naturally by a male and female were presented at double rate and 3 intensities (/bεt/, /dεt/, and /gεt/ at 45, 65 and 75 dB SPL). Intracellular recordings were made in 12 neurons, eight of which had a response to pure tones typical of spherical bushy neurons, responding in a primary-like (PL) fashion. The remaining cells were classified as either globular bushy (n=2) or stellate cells (n=2). In PL neurons, the VOT period was associated with hyperpolarisation. The duration and amplitude of this hyperpolarising influence was greater for female speech. These PL units showed better encoding of VOT than other cell types in which hyperpolarisation was less evident and action > potentials were often evoked during this period at the highest intensity level. We propose that this hyperpolarisation is due to stimulation of inhibitory sidebands by the high frequency frication noise within the VOT period. This inhibition reduces the probability of action potential generation during the VOT period and enhances the salience of the voice onset enabling more effective encoding of VOT than seen in the auditory nerve.