Graeme Clark Collection
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ItemCochlear implant place psychophysics: 1. Pitch estimation with deeply inserted electrodes( 1996)Numerical estimation of pitch was performed by 8 adult subjects implanted with cochlear prostheses manufactured by Cochlear Limited. The electrode arrays had been inserted into the scala tympani to between one and one and a half turns of the cochlea. Using bipolar stimulation, the pitch estimates for each subject showed an overall reduction with insertion depth of the stimulated electrode. However, for several subjects, after decreasing regularly for the more basal electrodes, pitch estimates showed an abrupt decrease, followed in some cases by a region of low pitch. Two of the subjects, implanted with a modified electrode array, the '20 + 2' which allowed monopolar in addition to bipolar stimulation, exhibited an abrupt decrease in pitch estimate with bipolar but not with monopolar stimulation. In these two subjects, for stimulating electrodes inserted more deeply than about three quarters of a turn, bipolar stimuli produced lower pitch sensations, and presumably more apical neural excitation patterns, than monopolar stimuli.
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ItemCochlear implant place psychophysics: 2. Comparison of forward masking and pitch estimation data( 1996)Results for forward masking and numerical estimation of pitch were compared in a group of 6 adult subjects implanted with cochlear prostheses manufactured by Cochlear Limited. Data were collected for bipolar +1 stimulation in all subjects, and for stimulation in one other mode, either common ground or monopolar, for all subjects but one. The pitch data show various irregularities and in each case can be seen to be broadly consistent with the corresponding forward masking data. It is shown that a 'centre of gravity' of the forward masking distribution varies with masker electrode in a manner that is qualitatively very similar to the variation of pitch estimate. It is suggested that, while pitch estimation results are consistent with those from forward masking, the latter contain more detailed information that may be useful in understanding intersubject variations in speech comprehension.
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ItemIs deep insertion of the cochlea implant electrode array necessary and possible?( 1995)Hyaluronate (Healon TM) appears to be useful in achieving deeper electrode insertions than are generally achieved at present. However, biosafety studies are still being conducted. If found to be a safe technique, further work to explore different electrical stimulation strategies and speech processing schemes will also need to be undertaken. This work is ongoing.
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ItemInitial investigation of the efficacy and biosafety of sodium hyaluronate (healon) as an aid to electrode array insertion( 1995)Stimulation of residual neural elements by electrodes inserted into the cochlea to produce the perception of speech and environmental sounds in profoundly deaf people is a fundamental aim of cochlear implantation. The multiple-channel cochlear implant utilizes the tonotopic arrangement of the organ of Corti to also achieve place pitch perception by stimulating different electrode bands. It may be possible to improve the range of pitches perceived by present cochlear implant patients by inserting the electrode array more deeply. To help achieve this, investigators have used sodium hyaluronate as a lubricant for electrode insertions. 1 It was felt deeper insertions were produced with sodium hyaluronate. Before introducing this substance as part of the surgical protocol for the Melbourne Cochlear Implant Clinic, it was decided to investigate its efficacy in aiding deeper insertions of the electrode. In addition, it was also necessary to determine if sodium hyaluronate, in conjunction with cochlear implantation, had adverse effects on the inner ear. This study was undertaken to address these issues.
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ItemA portable programmable digital sound processor for cochlear implant research( 1993)A programmable sound processor which utilizes digital signal processing has been developed for hearing prosthesis research. It incorporates a Motorola DSP56001 integrated circuit, 32K words of memory, a 12 b analog-to-digital converter, and a data formatter and transmitter which conveys control codes to the receiver-stimulator of a cochlear implant. The processor is pocket-sized and battery powered. It has been programmed to emulate the Spectral Maxima Sound Processor for the University of Melbourne/Nucleus 22 electrode implant, and is currently being used by several implantees. In continuing research, speech processing programs are being improved, and other applications, including signal processing for binaural implants and advanced hearing aids, are being developed.