Graeme Clark Collection

Permanent URI for this collection

Search Results

Now showing 1 - 5 of 5
  • Item
    Thumbnail Image
    Lateral inhibition in ventral cochlear nucleus chopper neurons: contribution to coding of a speech feature [Abstract]
    Needham, K. ; Paolini, A. G. ; Clarey, J. C. ; Clark, Graeme M. ( 2002)
    Lateral inhibition in the auditory system enhances excitatory responses by suppressing off-best frequency (BF) neural activity. Previous work has suggested that lateral inhibition activated by high frequency frication noise associated with stop consonant plays a role in coding voice onset time (VOT), the period between consonant release and onset of the ensuing vowel.
  • Item
    Thumbnail Image
    Improved sound processing for cochlear implants
    James, C.J. ; Just, Y. ; Knight, M.R. ; Martin, L.F.A. ; McKay, C.M. ; Plant, K.L. ; Tari, S. ; Vandali, A.E. ; Clark, Graeme M. ; Cowan, R.S.C. ; McDermott, H. J. ; Blamey, P. J. ; Dawson, P. ; Fearn, R. A. ; Grayden, D. B. ; Henshall, K. R. ( 2002)
    Four signal processing schemes currently under development aim to improve the perception of sounds/ especially speech, for children and adults using the Nucleus cochlear implant system. The schemes are (1) fast-acting input-signal compression, (2) Adaptive Dynamic Range Optimisation (ADRO), (3) TESM, a scheme that emphasises transients in signals, and (4) DRSP, a strategy that applies different stimulation rates to selected sets of electrodes.
  • Item
    Thumbnail Image
    A continuous supply of BDNF is necessary for sustained auditory neuron survival in deafened guinea pigs
    Gillespie, L. N. ; Clark, Graeme M. ; Bartlett, P. F. ; Marzella, P. L. ( 2002)
    Neurotrophic factors are well known to be involved in the development and maintenance of the auditory system, and have also been reported to act as survival factors for auditory neurons in 90th in vitro and in vivo deafness models. In this study we tested the longevity of the survival effects of brain-derived neurotrophic factor (BDNF) on auditory neurons in deafened guinea pigs -specifically, we aimed to determine if a single dose of BDNF is sufficient to maintain auditory neuron survival following loss of hair cells, or whether sustained delivery is required. Normal hearing guinea pigs were bilaterally deafened, and the left cochleae infused with 200 µl of BDNF (62.5µg/ml) over a period of 28 days via a cannula connected to a mini-osmotic pump. The right cochleae acted as deafened and untreated internal controls. Survival periods following the completion of the BDNF treatment varied from zero to two or four weeks. For all surgical procedures. guinea pigs were anaesthetised using ketamine (40mglkg) and xylazil (4mg/kg). Treatment with BDNF prevented the degeneration of auditory neurons normally seen following loss of hair cells, however, upon cessation of BDNF delivery, auditory neuron survival rates dropped rapidly, indicating that if trophic factor therapy is to be used in the treatment of hearing loss, continuous delivery is likely to be necessary.
  • Item
    Thumbnail Image
    Factors affecting speech perception outcomes for older children using multichannel cochlear implants
    Dowell, Richard C. ; Dettman, Shani J. ; Hill, Katie ; Winton, Elizabeth ; Hollow, Rod ; Clark, Graeme M. ( 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.
  • Item
    Thumbnail Image
    Post-implant habilitation for children using cochlear implants: effects on long-term outcome
    Dowell, Richard C. ; Dettman, Shani J. ; WILLIAMS, SARAH ; TOMOV, ALEXANDRA ; Hollow, Rod ; Clark, Graeme M. ( 2002)
    Most clinicians working in the cochlear implant field advocate a regular habilitation program for young children receiving implants. The development of auditory skills and the incorporation of these skills into language development are thought to be key areas for such programs. Studies of speech perception and language outcomes demonstrate that an educational approach that emphasises spoken language development appears to enhance the results for implanted children. It remains difficult, however, to demonstrate clearly the effect of habilitation objectively and to determine how much individual attention is desirable for each child. This pilot study considered the long term speech perception and language outcomes for two groups of children who received Nucleus cochlear implants in Melbourne. One group (n=17) was identified as receiving regular habilitation from the Melbourne Cochlear Implant Clinic over a four year post-operative period. Another group (n=l1) was identified as receiving very little regular habilitation over the post-operative period. The language and speech perception results for these two groups showed a significant difference in performance on a wide range of measures with the group receiving regular formal habilitation demonstrating 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. Further studies are needed to clarify these results on a larger group of children, and to control for additional confounding variables. Nonetheless, these preliminary results provide support for the incorporation of regular long-term habilitation into cochlear implant programs for children.