Graeme Clark Collection

Permanent URI for this collection

http://hdl.handle.net/11343/375

Filters

1977 - 1979 1 1990 - 1995 2
Reset filters

Settings
Statistics
Citations
Start date: 1970 × Subject: cochlear ×

Search Results

Now showing 1 - 3 of 3
  • Item
    Thumbnail Image
    A comparison of burst and amplitude modulated electrical stimulation of the cochlear
    Lithgow, Brian J. ( 1992)
    On average, the maximum firing rates of cells in the inferior colliculus, when stimulated with either bursts or ramps (amplitude modulated bursts) of biphasic pulsatile electrical stimuli, increased as the pulse rate was increased from 125 to 4000 pulses per second (pps). The fact that this firing rate has increased, on average, up to 4000 pps is evidence that a mechanism for high pulse rate discriminability exists. This firing rate increase was not on a 1:1 basis with the stimulus, but rather a time-averaged firing rate determination. Ramp stimuli generate a wider dynamic range of firing rates than those of burst stimuli, suggesting the potential for a higher rate of information transfer for cochlear implant patients. The finding of temporal information in transient “onset” responses (a response seen only in the first 10 ms post-stimulus onset) of ramp-evoked responses-more than burst-evoked responses-support high pulse rate discriminability and the use of ramp stimuli for encoding high pulse rate information to implant patients.
  • Item
    Thumbnail Image
    A multiple-electrode hearing prosthesis for cochlear implantation in deaf patients
    Clark, Graeme M. ; Black, R. ; Dewhurst, D. J. ; Forster, I. C. ; Patrick, J. F. ; Tong, Y. C. ( 1977)
    A multiple-electrode hearing prosthesis for cochlear implantation in deaf patients has been developed at the University of Melbourne. It has been designed as a multiple-electrode implant to provide the best chance of enabling patients to understand speech. It has been shown that an electrode array can be threaded along the coils of the inner ear close to residual auditory nerves. Experimental studies have indicated that the long-term implantation of the array will not lead to significant degeneration of auditory nerve fibres. Loss of platinum from the stimulating electrodes can be minimized with a biphasic constant current pulse, where the first phase is negative with respect to ground. The receiver-stimulator component has also been designed to provide 10 - 15 channels of stimulation. Furthermore, the phase and amplitude of the stimuli to individual electrodes can be varied to enable the localization of the electrical fields to discrete groups of nerve fibres, and the correct method of frequency and intensity coding to be determined. Finally, the device should be used in the first instance for a specially selected group of adults who are post-lingually deaf.
  • Item
    Thumbnail Image
    Response properties of neurons in the anteroventral cochlear nucleus of the cat to complex temporal patterns of electrical stimulation [Abstract]
    Brown, M. ; Paolini, A. G. ; Clark, Graeme M. ( 1995)
    Complex temporal patterns of electrical stimulation may provide a better simulation of the acoustic input. Currently little is known about the physiological or psychophysical responses to variations of the time intervals between pulses and their relative amplitudes. This knowledge could lead to a new generation of speech processing strategies. In this investigation we are examining physiological responses of neurons in the anteroventral cochlear nucleus to electrical stimulation using the Melbourne/Cochlear scala tympani banded electrode array. Two stimulus paradigms are being investigated: (I) a 50 ms burst of charged balanced biphasic electrical pulses delivered at constant rates with varying amplitudes; and (2) pulse pairs with varying interpulse intervals. The synchrony and the effectiveness in eliciting neural responses under both stimulus conditions is determined with extracellular and intracellular recordings. The amplitude of depolarising potentials recorded intracellularly is being plotted as a function of electrical stimulus pulse rate. In neurons where depolarising potentials are shown to be excitatory postsynaptic potentials, the latency of the evoked response is examined in order to determine whether they are of mono or polysynaptic origin. Neurons in this nucleus are also morphologically characterised and correlated with their physiological response properties. Discharge synchrony and entrainment are shown to be inversely proportional to stimulus pulse rate. Discharge synchrony is dependent on interpulse interval between the pulse pair.