Graeme Clark Collection
Permanent URI for this collection
Search Results
1 - 8 of 8
-
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.
-
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.
-
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.
-
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.
-
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.
-
ItemSpatial spread of neural excitation in cochlear implants: comparison of measurements made using NRT and forward masking [Abstract]( 1998)Recently developed technology allows intracochlear potentials to be measured in cochlear implant recipients, using telemetry. Neural response telemetry (NRT) enables the measurement of compound action potentials evoked by stimulation of cochlear implant electrodes. These objective measures can now be compared with related psychophysical measures in humans. We will present data, from both NRT and forward masking, on spatial spread of neural excitation due to stimulation of cochlear implant electrodes. The response fields from more apical neurons will spread quite broadly to the sensing electrodes of an implanted array, resulting in misleadingly broad NRT estimates of the spatial spread of neural excitation. Forward masking, which might itself lay claims to some degree of "objectivity", will not suffer from this limitation. Comparison of data from the two measures will help to determine the limitations of NRT as a tool for measuring spatial spread of neural excitation.
-
ItemThe development of a precurved cochlear implant electrode array and its preliminary psychophysical evaluation [Abstract]( 1998)A precurved banded electrode array may provide a better interface with the auditory neural pathways for cochlear implants, and provide better speech perception. A prototype arrray has been further evaluated for ease of insertion, siting within the cochlea and induction of any cochlear trauma. The arrays were inserted into the human cochlear under simulated surgery. The bones were embedded in Araldite, X-rayed and sectioned. X-ray reconstruction analyses of the position of the implanted array showed its insertion to be favourable. Cochlear implants with precurved arrays have been implanted in three patients. Psychophysical evaluation and X-ray analyses have shown that as electrode distance from the modiolus decreased: threshold current decreased; dynamic range increased; current spread as measured by forward masking studies, was more focused; electrode discrimination with loudness jitter (being abetter representation of the dynamic speech signal) improved; JNDs for loudness, expressed as a function of dynamic range, decreased.
-
ItemPsychophysics and speech perception with a premodiolar electrode array( 1997)A perimodiolar electrode array, designed to lie closer to the modiolus than the standard Coclear Limited array and developed by the Cooperative Research Centre for Cochlear Implant, Speech and Hearing Research in conjunction with Cochlear Limited, has recently been implanted in an adult patient. While excellent speech results have been obtained using the standard array, it is hypothesised that the improved place coding expected from an array lying closer to the modiolus would result in improved speech perception. Analysis of a modified Stenvers view X-ray revealed that the most apical electrode was inserted to an angle of 311 0 and that the apical half of the array was considerably closer to the modiolus than would have been the case for a standard array. Thresholds and comfortable levels were correlated with the lateral position of the stimulated electrode in the scala tympani, being much reduced for the apical electrodes. Forward masking and electrode discrimination are being measured in order to study the spread of neural excitation and the distinctness of percepts for different electrodes.