Graeme Clark Collection
Permanent URI for this collection
Search Results
1 - 10 of 18
-
ItemA speech processing strategy for an electro-tactile vocoder [Abstract]( 1980)Past attempts at using the skin for recognition of tactile patterns derived from acoustic speech signals have largely been unsuccessful for perception of running speech. Problems facing researchers in this field include: frequency discrimination, especially for electrical stimulation, temporal and spatial resolution, real time speech processing and tactile pattern configuration strategies. It is considered that recent developments in speech processing which allow real time estimation of formant frequencies and vocal tract area functions will enable a successful speech aid to be developed. Based on results of the Tadoma (or Hofgaard) Method, in which speech is perceived by the deaf-blind using tactile and kinesthetic senses to determine movements of a speaker's articulators, a model is evaluated which enables a tactile display of articulatry information derived from parameters extracted from the speech signal by real time speech processing. Psychophysical measurements of percepts of computer derived patterns were carried out concentrating in particular on patterns more likely to be important for phonemic and speech discrimination. In this way it is hoped to validate the model as a useful speech aid for the profoundly and partially deaf.
-
ItemScanning electron microscopy of chronically stimulated platinum intracochlear electrodes( 1985)Platinum electrodes were examined for evidence of corrosion using a scanning electron microscope (SEM). In vivo electrodes stimulated using charge-balanced biphasic pulses for periods of up to 2000 h at charge densities of 0.18-0.32 µC mm-2 geom. per phase, were compared with in vitro electrodes stimulated in inorganic saline using similar stimulus parameters, and with in vivo control electrodes. The in vitro stimulated electrodes showed evidence of platinum corrosion at high charge density and aggregate charge injection. Significantly, the in vivo stimulated electrodes showed no evidence of stimulus induced corrosion. Indeed, their surfaces were similar to the in vivo control electrodes. In vitro electrochemical studies have demonstrated that proteins play a significant role in the inhibition of platinum dissolution: the present study has demonstrated an inhibitory effect in vivo. This may be due to the presence of proteins.
-
ItemTwo-component hearing sensations produced by two-electrode stimulation in the cochlear of a deaf patient( 1983)http://www.sciencemag.org/cgi/content/abstract/219/4587/993?ijkey=v6jEOhdpzPCxw&keytype=ref&siteid=sci
-
ItemPercepts from scala tympani stimulation( 1983)This report summarizes the characteristics of the hearing sensations produced by electrical stimulation using scala tympani electrodes in a postlingually deaf patient (MC1) at the University of Melbourne. An array of 10 electrodes, spaced 1.5 mm apart, was inserted through the round window for a distance of 15 mm around the scala tympani. Biphasic current pulses with each phase fixed at 180 /μsec were used. Fifteen current levels from 67 /μA to 1 rnA could be assigned in 67-/μA steps, and a maximum repetition rate of 1000 rep/sec was possible. More detailed descriptions of the stimulation hardware and the patient's history can be found in previous reports.
-
ItemThe histopathological effects of chronic electrical stimulation of the cat cochlea(Cambridge University Press, 1983)The success of a cochlear implant depends on stimulating an adequate number of viable spiral ganglion cells. The effect of chronic electrical stimulation on ganglion cells is therefore an important consideration when assessing the effectiveness and safety of such a device. The histopathological assessment of chronic unstimulated intracochlear electrodes is now well documented (Simmons, 1967; Clark, 1973; Clark et al, 1975; Schindler and Merzenich, 1974; Schindler, 1976; Schindler et al, 1977; Sutton et al, 1980). These experimental studies have used a variety of electrode designs, materials and surgical techniques. However, all have shown that chronic implantation has little effect on the peripheral nerves and the spiral ganglion cells adjacent to an implant, provided the insertion procedure is free of trauma and infection.
-
ItemPhysiological and histopathological effects of chronic intracochlear electrical stimulation(Monash University Press, 1983)Direct and r.f. currents are known to result in destruction of neural tissue. However, it is now apparent that non-destructive electrical stimulation can be achieved by the use of biphasic pulsatile stimuli (Lilly, 1960; Mortimer et al., 1970; Hughes et al., 1980). Although maximum biologically safe stimulation regimes have yet to be clearly defined, the evidence of a number of investigators suggests that charge density per phase and charge injection per phase are important parameters when establishing biologically safe levels of electrical stimulation (Pudenz et al., 1975; Pudenz et al., 1977; Brown et al., 1977; Babb et al., 1977). Furthermore, considerable attention has been given to ensure that the stimulus is not producing adverse electrochemical reactions that could result in physical or toxic injury to the biological environment. Brummer et al. (1977) have defined the upper limit of electrochemically safe electrical stimulation for platinum electrodes as charge balanced biphasic pulses at a maximum charge density of 300 ?C/cm2 geom./phase.
-
ItemChronic electrical stimulation of the auditory nerve in cats: physiological and histopathological results( 1983)The ability of spiral ganglion cells to survive long-term electrical stimulation is a precondition for the success of cochlear prostheses. In this study 10 cats were implanted bilaterally with bipolar scala tympani electrodes and stimulated for periods of up to 2029 hours using charge balanced biphasic current pulses. The status of the auditory nerve was monitored periodically by recording electrically evoked auditory brainstem responses. At the conclusion of the stimulation program, spiral ganglion cell survival was assessed for stimulated and control cochleas; comparison of the two groups showed no statistically significant difference. The results of this study indicate that long-term intracochlear electrical stimulation using carefully controlled biphasic pulses does not adversely affect the spiral ganglion cell population.
-
ItemClinical trial of a multiple-channel cochlear prosthesis: an initial study in four patients with profound total hearing loss( 1983)The clinical trial of a multiple-channel cochlear prosthesis was undertaken in four patients with postlingual deafness and profound total hearing loss. The results of open-set speech tests confirmed that, using electrical stimulation alone, one patient could have a meaningful conversation with resorting to lipreading (for example, this patient uses the prosthesis to converse with her husband on the telephone). The results of closed-set speech tests also suggested that a multiple-channel stimulator is more effective than a single-channel one in conveying speech information. The cochlear prosthesis was especially effective in all four patients when it was used in conjunction with lipreading, and speech-tracking tests showed that the patients could combine the information obtained from both electrical stimulation and lipreading.
-
ItemAmplitude and pulse rate difference limens for electrical stimulation of the cochlea following graded degeneration of the auditory nerve( 1983)Experimentally deafened cats with differing populations of residual spiral ganglion cells were implanted with cochlear electrodes and were electrically stimulated. They were conditioned to respond to changes in electrical pulse rate amplitude, and both electrical pulse rate and amplitude difference limens were determined. It was found that although there were some variations in difference limens between animals, these showed no correlation with residual cell populations over the range 8-44%.
-
ItemCurrent distributions in cochlear stimulation( 1983)The success of a multiple-channel cochlear implant depends, in part, on localizing the electrical current to discrete groups of auditory nerve fibers. A number of studies are described that were performed to investigate this issue. First, a three-dimensional resistance model of the normal cat cochlea was developed to examine general properties of electrically stimulating the cochlea. The distribution of the excited nerve fibers for monopolar and bipolar stimulation of the cat scala tympani were then determined. In addition certain measurements of the current distribution within the human cochlea for a pseudobipolar electrode array were performed. Finally, measurements were made in saline-solution-filled tube models of current distributions for bipolar and pseudobipolar stimulation, with both single-electrode and coincident multi-electrode stimulation. (From Introduction)