Graeme Clark Collection
Permanent URI for this collection
Search Results
1 - 10 of 34
-
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.
-
ItemIntracellular responses of anteroventral cochlear nucleus neurones to intracochlear electrical stimulation in the rat [Abstract]( 1996)The anterior division of the ventral cochlear nucleus (AVCN) is the first relay station of the auditory pathway. Currently little is known about the intracellular physiological responses of neurones in the AVCN to electrical stimulation of the cochlea. We investigated the effect of cochlear electrical stimulation in the rat AVCN using in vivo intracellular recordings. Male rats were anaesthetised with urethane (1.3g/kg i.p), placed in a stereotaxic frame, the crania and dura removed and the cochlear nucleus exposed.
-
ItemElectrophonically driven single unit responses of the anteroventral cochlear nucleus in cat [Abstract]( 1996)Electrical stimulation of the cochlea results in both direct and electrophonic excitation of auditory nerve fibres. It has been proposed that electrophonic stimulation results from the creation of a mechanical disturbance on the basilar membrane which has properties similar those resulting from acoustic stimuli. Auditory nerve compound action potential (CAP) forward masking studies1 show the level of frequency specific electrophonic stimulation is highly correlated with the spectral energy of the electrical stimulus waveform. The level of spectral energy in pulsatile biphasic electrical stimuli decreases toward low frequencies suggesting the level of electrophonic stimulation will be diminished in the low frequency region of the cochlea.
-
ItemReduction in excitability of the auditory nerve in guinea pigs following acute high rate electrical stimulation [Abstract]( 1996)Electrical stimulation of neural tissue involves the transfer of charge to tissue via electrodes. Safe charge transfer can be achieved using biphasic current pulses designed to reduce the generation of direct current (DC) or the production of electrochemical products. However, neural stimulators must also use capacitors in series with electrodes, or electrode shorting between current pulses, to further minimize DC due to electrode polarization.
-
ItemResponse thresholds to frequency modulated sound and electrical stimulation of the auditory nerve in cats( 1973)A previous study (Clark et al., 1972) has shown the effects of rate, current and site of electrical stimulation of the cochlea and central auditory pathways on cats' behavioural thresholds. It was observed that the thresholds were lower for low rates of electrical stimulation of the basal or high frequency end rather than the apical or low frequency end of the cochlea.
-
ItemPhysiological and histopathological effects of chronic monopolar high rate stimulation on the auditory nerve( 2000)Speech processing strategies based on high rate electrical stimulation have been associated with improvements in speech perception among cochlear implant users. The present study was designed to evaluate the electrophysiological and histopathological effects of long-term intracochlear monopolar stimulation at the maximum stimulus rate of the current Nucleus Cochlear implant system (14493 pulses/s) as part of our ongoing investigations of safety issues associated with cochlear implants
-
ItemAdvances in relating cochlear implant physiology and psychophysics [Abstract]( 1999)More than a decade has passed since apparent discrepancies between physiological and psychophysical thresholds in cochlear implant users were first pointed out. This incongruity has been largely ignored in the intervening time. In a recent series of studies we have undertaken to determine if the definition of threshold in physiological studies is the cause of these differences. Analysis of auditory nerve physiology indicates that fluctuations in the membrane potential are a significant source of stochastic activity (noise) in electrical stimulation, such that responses are best described by discharge probability as a function of stimulus intensity, rather than just a simple deterministic (zero-noise) threshold. We hypothesize that quite low discharge probabilities in individual fibers may be sufficient to account for psychophysical thresholds, if responses in a population of fibers are used in this task by higher auditory pathways.
-
ItemInsertion study using new peri-modiolar electrode array designs [Abstract]( 1999)Intracochlear multi-channel cochlear implants have been shown to successfully provide auditory information for profoundly deaf patients by electrically stimulating discrete populations of auditory nerve fibers via a scala tympani (ST) electrode array. Histological and radiological examination of implanted human temporal bones showed that the current straight Nucleus® array is usually positioned against the outer wall of the ST. An electrode array close to the modiolus could be expected to reduce stimulation thresholds and result in a more localized neural excitation pattern.
-
ItemTemporal response properties of primary-like units in the anteroventral cochlear nucleus to acoustic and electrical stimulation [Abstract]( 1998)Auditory information is encoded in the central auditory pathway in both the spatial and temporal domains. The magnitude of the contributing role of each domain remains unresolved. Scala tympani electrical stimulation of the auditory pathway may provide insights into the relative importance of these different coding domains. This study investigates the temporal response of acoustically-characterised primary-like units in the anteroventral cochlear nucleus (AVCN) to acoustic and electrical stimulation. Response synchrony to acoustic stimulation at and below the units characteristic frequency (CF) and to electrical stimulation at rates up to 1000 Hz has been analysed with respect to the phase of the stimulus and the intervals between successive spikes. Normal hearing adult cats were anaesthetised with pentobarbitone sodium (Nembutal; 45 mg/k.g l.V.) and the AVCN exposed via a dorsal approach. Micropipette electrodes (4 -30 M?) were advanced dorsoventrally through the AVCN and the response timing of isolated units recorded on computer for off-line analysis. To compare the variance in the timing of the response with respect to the phase of the stimulus and with respect to the intervals between successive responses, cross correlation of spike timing and cross-correlation of spike intervals were performed. For acoustic stimulation these results show that the variance in the timing of the response with respect to the phase of the stimulus is lower (i.e. higher correlation) than that seen in the interval variance. A similar result was not however found following electrical stimulation. Cross-correlations on different order intervals, (i.e. 1st, 2nd, 3rd etc.), show that variance across the different order intervals does not systematically vary. These data suggest that the temporal response to acoustic stimuli at this level of the auditory pathway more precisely codes stimulus phase than stimulus interval.
-
ItemPrediction of variance in neural response to cochlear implant stimulation and its implications for perception [Abstract]( 1997)Cochlear implant patients' perception of sound is derived via electrical pulses arising from an electrode array. Chosen aspects of the acoustic spectrum are coded via a stimulation pattern designed according to some sound coding algorithm. Thus, a patients' ability to discriminate between sounds, and in turn their understanding, is directly related to their ability to differentiate between the patterns of electrical stimulation which code various sounds.