Graeme Clark Collection
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ItemAuditory evoked potentials and auditory sequential memory [Abstract]( 1974)The evaluation of intelligence in infants and young children is important in assessing their prognosis and institutional placement, and is difficult with present clinical methods. Therefore, the recent studies which show a correlation between visual evoked responses and intelligence are of value. It is also of importance to determine if auditory evoked potentials may be used in assessing children with communication disorders, as their defect frequently involves the auditory system, and they will often require evoked response audiometry to exclude loss of hearing from the diagnosis.
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ItemAuditory evoked responses to frequency and amplitude modulated sound( 1973)Auditory evoked responses to pure tone bursts have been described in a number of studies and have been characterized by the P1, N1 and P2 components. The presence of later components, namely N2, P3 and the Contingent Negative Variation, depends largely on the cerebral processing of the stimulus. These evoked responses have been recorded using tone bursts. However, neurophysiological studies have shown that the cortex codes complex sounds. Therefore, we performed a set of acute experiments on the cat, using frequency and amplitude modulated sounds. This was reported in a previous study (Richards and Clark, 1972) which showed that similar onset and later waves could be recorded from the cortex of the cat. In some areas of the cortex the later waves were in synchrony with the modulation envelope.
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ItemSurface negative potential shifts in the auditory cortex( 1973)A number of investigations have shown that cortical surface negative potential shifts may occur in response to peripheral and central stimulation, and accompany various behavioural states. The present study is an attempt to indicate some of the important variables in producing a surface negative shift in the auditory cortex. The purpose of this was to help determine whether this phenomenon might play some role in sensory memory.
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ItemThe design of an ear bar system for auditory neruophysiological research( 1972)Absolute sound intensity measurements at the ear drum are important in auditory research. Previous attempts to measure sound intensity using a small bore probe tube coupled to a microphone have proved unsatisfactory. In the present investigation an alternative system employing two condenser microphones coupled to the input end of the ear bar was used to estimate the sound intensity at the ear drum. Consideration was also given to minimizing harmonic distortion and resonance in the system.
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ItemCochlear implant: perspectives( 1979)Volta, who discovered the electrolytic cell, was the first person to stimulate the auditory system electrically. He connected a battery to two metal rods which were inserted into his ears, and he received "une secousse dans 1a t�te". In spite of his experience, interest in stimulating the auditory system electrically as a cure for profound hearing loss has persisted, and a number of attempts have been made as electronic developments have occurred. Following the introduction of the thermionic valve more precise studies of the effects of rate and intensity were possible. Then direct stimulation of the auditory nerve at surgery, to determine parameters of electrical stimulation, were carried out. These were followed by a few long term patient implantations in which the wires were connected directly to the outside through the skin. As this carries a high risk of infection, long term single electrode studies were also performed in which the stimuli were transmitted by inductive coupling to a coil buried beneath the skin. During this period developments in electronics and computers also led to acute and behavioural studies on animals to learn more about the physiology of hearing and the effects of electrical stimulation. All the results indicate that a multiple-electrode system offers the best chance of providing speech for a patient. A multiple-electrode system requires the implantation of a much more complicated electronic device which can now be miniaturized to an appropriate size.