Graeme Clark Collection

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 57
  • Item
    Thumbnail Image
    A preliminary report on a multiple-channel cochlear implant operation
    Tong, Y. C. ; Black, R. C. ; Clark, Graeme M. ; Forster, I. C. ; Millar, J. B. ; O'Loughlin, B. J. ; Patrick, J. F. (Cambridge University Press, 1979)
    Intra-cochlear single-channel electrical stimulation has recently been attempted by Michelson (1971) and by House and Urban (1973). Douek et at. (1977) have described experiments with a single-channel promontory electrode system. It is generally accepted that a single-channel system is useful in conveying crude auditory information such as the presence of sounds and some prosodic features of speech (Bilger et al., 1977; Douek et al., 1977). (From Introduction)
  • Item
    Thumbnail Image
    Critical bands following the selective destruction of cochlear inner and outer hair cells
    Nienhuys, Terry G. W. ; Clark, Graeme M. ( 1979)
    Critical bandwidths and absolute intensity thresholds were measured in cats before and after kanamycin treatment which induced selective inner and outer hair cell losses. Hair cell losses were measured from cochleograms constructed from surface preparations of the organ of Corti. Results suggested that, for the test frequencies and stimulus intensities employed, critical bandwidths were not affected for frequencies tonotopically located in cochlear regions where only outer hair cells were lost. Critical bands were widened or not measurable only when inner hair cell losses exceeding 40% were also associated with complete loss of outer hair cells. The experiment suggests that cochlear frequency selectivity can be mediated by inner hair cells alone.
  • Item
    Thumbnail Image
    The surgery for multiple-electrode cochlear implantations
    Clark, Graeme M. ; Pyman, Brian C. ; Bailey, Quentin R. (Cambridge University Press, 1979)
    The multiple-electrode hearing prosthesis designed in the Departments of Otolaryngology and Electrical Engineering (UMDOLEE) at the University of Melbourne (Clark et al., 1977) has been miniaturized with hybrid circuitry so that, if design changes are necessary as a result of initial patient testing, they can be made at minimal cost. This results, however, in increased package dimensions which makes its placement and the design of the surgery more critical. This problem is increased by the fact that we have considered it important to be able to remove the package and replace it with another without disturbing the implanted electrode array, should the first receiver-stimulator fail or an improved design become available. This has meant the design of a special connector (Patrick, 1977; Clark et al., 1978) which adds to the dimensions of the implanted unit. In addition the placement of the coils for transmitting power and information has to be considered. Not only is it desirable to site the coils at a convenient location behind the ear to facilitate the placement and wearing of the external transmitter, but there should also be no relative movement between the coils and the electronic package. These design considerations have led to the sitting of the coils on top of the hermetically-sealed box, and further increased the height of the package. The dimensions of the package shown in Fig. 1 are length 42 mm, width 32 mm, height of connector 8.5 mm, height of receiver-stimulato unit 13 mm. The surgical considerations discussed are the result of a number of temporal bone and cadaver dissections, and the surgical implantation at The Royal Victorian Eye and Ear Hospital of the UMDOLEE unit in a specially-selected patient.
  • Item
    Thumbnail Image
    A cochlear implant round window electrode array
    Clark, Graeme M. ; Patrick, J. F. ; Bailey, Q. (Cambridge University Press, 1979)
    One important aspect of cochlear implantation is the placement of a multiple-electrode array close to residual auditory nerve fibres so that discrete groups of fibres can be stimulated electrically according to the place basis of frequency coding. Furthermore, in patients who are postlingually deaf these electrodes should lie in relation to the nerve fibres which are responsible for transmitting the frequencies which are important in speech comprehension, viz. 300-3,000 Hz. The method of electrode insertion should also ensure that there is no significant damage to auditory nerve fibres.
  • Item
    Thumbnail Image
    Frequency discrimination following the selective destruction of cochlear inner and outer hair cells
    Nienhuys, Terry G. W. ; Clark, Graeme M. ( 1978)
    http://www.sciencemag.org/cgi/content/abstract/199/4335/1356?ijkey=OnDf2slSrU.DE&keytype=ref&siteid=sci
  • Item
    Thumbnail Image
    Critical bandwidth in the cat following the selective destruction of cochlear inner and outer hair cells [Abstract]
    Nienhuys, T. G. W. ; Clark, Graeme M. (Australian Physiological and Pharmacological Society, 1978)
    It is of interest to determine the significance of the inner and outer hair cells of the cochlea in critical bandwidth measurements, as there is evidence for a difference in their roles in frequency selectivity (Dallos et at., 1977) and in frequency discrimination (Nienhuys and Clark, 1978). The present study has been undertaken on-four monauralized cats which were trained to respond by a conditioned suppression technique. Behavioural auditory thresholds were measured by plotting suppression ratios for frequencies of 1kHz, 4kHz, 8kHz, 10kHz, 12kHz and 16kHz. Critical bands were measured at the same frequencies by recording the pure tone thresholds in the presence of a masking noise with six different bandwidths, a constant total power, and geometrically centred on the test tone (Greenwood, 1961). The cats were then given a series of intramuscular injections of kanamycin (200mg kg-l d- l ) for 10 days to selectively destroy the outer hair cells, and behavioural thresholds determined shortly afterwards. Critical bands were again measured at all the previous frequencies except 16kHz, where the auditory behavioural threshold was too high. At the completion of the experiments behavioural thresholds were re-determined, the animals were anaesthetized with pentobarbital sodium (40mg/kg, i.p.) and auditory nerve action potentials recorded.
  • Item
    Thumbnail Image
    A multiple-electrode cochlear implant
    Clark, Graeme M. ; Tong, Y. C. ; Bailey, Q. R. ; Black, R. C. ; Martin, L. F. ; Millar, J. B. ; O'Loughlin B. J. ; Patrick, J. F. ; Pyman, B. C. ( 1978)
    Interest in artificially stimulating the auditory nerve electrically for sensori-neural deafness was first sparked off by Volta in the 18th century. Count Volta, who was the first to develop the electric battery, connected up a number of his batteries to two metal rods which he inserted into his ears. Having placed the rods in his ears he pressed the switch and received "une secousse dans la tete" and perceived a noise like "the boiling of thick soup".
  • Item
    Thumbnail Image
    Design criteria of a multiple-electrode cochlear implant hearing prosthesis
    Clark, Graeme M. ; Black, R. C. ; Forster, I. C. ; Patrick, J. F. ; Tong, Y. C. ( 1978)
    Abstract not available due to copyright.
  • Item
    Thumbnail Image
    Electrical network properties and distribution of potentials in the cat cochlea [Abstract]
    Black, R. C. ; Clark, Graeme M. (Australian Physiological and Pharmacological Society, 1978)
    The-patterns of electrical resistance and capacitance in the cochlea formed by the anatomical organisation of the tissue structures and fluids are important in determining the distribution of electrical potentials which arise during normal acoustic stimulation (von Bekesy,1951). Cochlear potential distributions have in the past been measured by recording from the scalar fluids both the spread of cochlear microphonics and also potentials due to electrical stimulation. However, similar distributions in the hair cell-nerve ending region of the organ of Corti may not necessarily occur because of current shunting effects due to the electrical network patterns. To examine these current shunting effects, a three dimensional mathematical model of the electrical properties of the cat cochlea was constructed. This was formed from a two dimensional cochlear cross-section model similar to that proposed by Johnstone et al., (1966) for the guinea pig. Sixteen such sections were resistively coupled to form the three dimensional model. Results derived from this model predict that during electrical stimulation of the cochlea, the current in the organ of Corti region attenuates quite differently to the scalar voltage by a degree which depends on the stimulus electrode configuration.
  • Item
    Thumbnail Image
    Frequency discrimination and critical bands following the selective destruction of cochlear inner and outer hair cells
    Nienhuys, T. G. W. ; Clark, Graeme M. ( 1977)
    The role of the inner and outer hair cells of the cochlea in frequency discrimination and critical band measurements is not clearly understood. There is, however, evidence for an interaction between the hair cells in threshold determinations (1) and frequency selectivity (2). Furthermore, although there is increasing evidence that a place theory is more importance than a periodicity theory in frequency coding the situation is still not clear, and the role of the inner and outer hair cells in frequency discrimination and critical band measurements should provide additional evidence to help clarify the situation.