Graeme Clark Collection
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ItemBDNF-induced survival of auditory neurons in vivo: cessation of treatment leads to accelerated loss of survival effects( 2003)Neurotrophic factors are important for the development and maintenance of the auditory system. They have also been shown to act as survival factors for auditory neurons in animal deafness models. Studies have demonstrated recently that these neurotrophic factors not only maintain survival of auditory neurons, but that these surviving neurons retain functionality. It remains to be determined, however, if a single administration of a neurotrophic factor is sufficient to maintain auditory neuron survival after loss of hair cells, or if sustained delivery is required. This study investigated the longevity of the survival effects of BDNF on auditory neurons in deafened guinea pigs. Briefly, the left cochleae of deafened guinea pigs were infused with BDNF for 28 days via a miniosmotic pump, and neuronal survival was analysed at various stages after the completion of treatment. BDNF treatment prevented the degeneration of auditory neurons that normally is seen after a loss of hair cells, supporting previous studies. Our results indicate, however, that cessation of BDNF treatment leads to an accelerated decline in auditory neuron survival as compared to that observed in deafened, untreated cochleae. These findings indicate that much work remains to be done to establish a technique for the long-term survival of auditory neurons in the deaf ear.
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ItemCochlear implants(Springer, 2003)Over the past two decades there has been remarkable progress in the clinical treatment of profound hearing loss for individuals unable to derive significant benefit from hearing aids. Now many individuals who were unable to communicate effectively prior to receiving a cochlear implant are able to do so, even over the telephone without any supplementary visual cues from lip reading. The earliest cochlear implant devices used only a single active channel for transmitting acoustic information to the auditory system and were not very effective in providing the sort of spectrotemporal information required for spoken communication. This situation began to change about 20 years ago upon introduction of implant devices with several active stimulation sites. The addition of these extra channels of information has revolutionized the treatment of the profoundly hearing impaired. Many individuals with such implants are capable of nearly normal spoken communication, whereas 20 years ago the prognosis for such persons would have been extremely bleak. (From Introduction)
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ItemCochlear implants in children: safety as well and speech and language( 2003)Unavailable due to copyright.
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ItemCognitive processing in children using cochlear implants: the relationship between visual memory, attention, and executive functions and developing language skills( 2002)We performed this study to determine whether children using a cochlear implant performed differently from age- and gender-matched hearing aid users on 8 neuropsychological measures of visual memory, attention, and executive functioning. The study also examined whether differences in cognitive skills could account for some of the observed variance in speech perception, vocabulary, and language abilities of hearing-impaired children. In contrast to previous studies, our results revealed no significant cognitive differences between children who use a cochlear implant and children who use hearing aids. Partial correlation analysis indicated that the children’s visual memory skills, i.e., their recognition memory, delayed recall, and paired associative learning memory skills, correlated significantly with their language skills. When examined at a significance level of .01, attention and executive functioning skills did not relate to the children’s developing speech perception, vocabulary, or language skills. The results suggested that differences in visual memory skills may account for some of the variance seen in the language abilities of children using implants and children using hearing aids.
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ItemSummation of spatiotemporal input patterns in leaky integrate-and-fire neurons: Application to neurons in the cochlear nucleus receiving converging auditory nerve fiber input(SPRINGER, 2002)The response of leaky integrate-and-fire neurons is analyzed for periodic inputs whose phases vary with their spatial location. The model gives the relationship between the spatial summation distance and the degree of phase locking of the output spikes (i.e., locking to the periodic stochastic inputs, measured by the synchronization index). The synaptic inputs are modeled as an inhomogeneous Poisson process, and the analysis is carried out in the Gaussian approximation. The model has been applied to globular bushy cells of the cochlear nucleus, which receive converging inputs from auditory nerve fibers that originate at neighboring sites in the cochlea. The model elucidates the roles played by spatial summation and coincidence detection, showing how synchronization decreases with an increase in both frequency and spatial spread of inputs. It also shows under what conditions an enhancement of synchronization of the output relative to the input takes place.
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ItemThe effect of language ability and residual hearing on speech perception outcomes for older children using multichannel cochlear implants [Abstract]( 2002)Early-deafened teenagers or young adults have shown somewhat disappointing performance with cochlear implants in the past, however, in recent years a proportion of older children have demonstrated excellent speech perception performance. There is a great deal of variability in speech perception performance within this group. It is important to investigate the factors influencing performance so that adolescents and their families can make informed decisions regarding cochlear implant surgery. This study considered a number of possible predictive factors in a group of 25 children implanted in Melbourne between the ages of 8 and 18 years. Subjects completed open set speech perception testing using BKB sentences both pre-and postoperatively, 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 post-operative communication mode. Multivariate analysis suggested that three factors were associated with postoperative speech perception performance. Results were improved for subjects with better pre-operative speech perception, better pre-operative language ability, and when the duration of profound hearing loss was shorter. 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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ItemThe effects of post-implant habilitation on long-term outcomes for children using multichannel cochlear implants [Abstract]( 2002)Those working in the cochlear implant field advocate a regular habilitation program for young children receiving implants. Developing auditory skills and the incorporating these into general language development are considered to be key areas for such programs. Investigations of speech perception and language outcomes have demonstrated that the emphasis of spoken language development appears to enhance the results for implanted children. It remains difficult, however, to demonstrate the effect of habilitation as a separate factor and to determine how much individual attention is desirable for each child. This preliminary study considered the long term speech perception and language outcomes for two groups of children who received Nucleus cochlear implants in Melbourne. The first group (n = 17) was identified as receiving regular habilitation from the Melbourne Cochlear Implant Clinic over a four year post-operative period. A second group (n = 11) was identified as receiving very little regular habilitation over the post-operative period. Language and speech perception results for these two groups showed significant differences in performance on a wide range of measures. The group who received regular, formal habilitation demonstrated better performance on all measures. These groups included only congenitally, profoundly hearing- impaired children and did not differ significantly on mean age at implant or experience at the time of assessment. A more comprehensive study is needed to clarify these results on a larger group of children, and to control for additional confounding variables. Nonetheless, these results provide support for the incorporation of regular long-term habilitation into cochlear implant programs for children.
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ItemPredicting speech perception results for children using multichannel cochlear implants [Abstract]( 2002)It is most helpful in counselling families considering cochlear implantation to have some ability to predict outcomes for individual hearing-impaired children. Speech perception results for open-set words and sentences have been collected for all children implanted with the Nucleus device in Melbourne. Assessments are available at approximately six month intervals following implantation, Data was collected for each child regarding type of hearing loss, duration and age at onset of profound hearing loss, age at implantation, pre and post-implant communication mode, developmental delay, speech coding scheme and implant experience. These data were used as predictor variables in step-wise multiple linear regression analyses with the speech perception scores as the dependent variables. Shorter duration of profound hearing loss, later onset of profound hearing loss, exclusively oral communication mode following implantation, and longer implant experience were associated with significantly (p < 0.00 I) improved open-set speech perception. The use of the SPEAK signal coding scheme was shown to provide significantly better speech perception performance for children (p < 0.00 I). Developmental delay was associated with poorer speech perception outcomes (p < 0.0 I). Over 50% of the variance in speech perception scores was accounted for by these variables. The study suggests that younger implantation for congenitally deaf children leads to improved speech perception results. On the other hand, the development of auditory language skills in implanted children may be as important as age at implantation in enhancing long term outcomes. Regression equations derived from these results can be used to predict outcomes for cochlear implant candidates with a reasonable accuracy.
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ItemSpeech perception outcomes in older children who use multichannel cochlear implants: Older is not always poorer(ANNALS PUBL CO, 2002-05)Speech perception outcomes for early-deafened children who undergo implantation as teenagers or young adults are generally reported to be poorer than results for young children. It is important to provide appropriate expectations when counseling adolescents and their families to help them make an informed choice regarding cochlear implant surgery. The considerable variation of results in this group makes this process more difficult. This study considered a number of factors in a group of 25 children who underwent implantation in Melbourne between the ages of 8 and 18 years. Each subject completed open-set speech perception testing with Bamford-Kowal-Bench sentences before and after implantation and preoperative language testing with the Peabody Picture Vocabulary Test. Data were collected regarding the type of hearing loss, age at implantation, age at hearing aid fitting, audiometric details, and preoperative and postoperative communication mode. Results were submitted to a stepwise multiple linear regression analysis with postoperative open-set sentence scores as the dependent variables. The analysis suggested that 3 factors have a significant predictive value for speech perception after implantation: preoperative open-set sentence score, duration of profound hearing loss, and equivalent language age. These 3 factors accounted for 66% of the variance in this group. The results of this study suggest that children who have useful speech perception before implantation, and higher age-equivalent scores on language measures, would be expected to do well with a cochlear implant. Consistent with other studies, a shorter duration of profound hearing loss is also advantageous. The mean sentence score for this group, 47%, was not significantly different from the mean result across all children in the Melbourne program.