Graeme Clark Collection
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ItemEvoked responses in humans to tones which are sinusoidally amplitude modulated [Abstract]( 1980)Evoked responses have been recorded from the scalp of normal human subjects to continuous sinusoidally-modulated Amplitude-modulated tones. The responses were periodic in nature, and a Fourier transform was used to quantify the amplitude and the phase of the constituent fundamental frequency and harmonic components. The fundamental frequency of the response equalled the frequency of the modulation envelope and the amplitude of the harmonic components was usually less than the fundamental. The responses were also found to be invariant with time for periods exceeding 30 minutes.
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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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ItemThe effects of muscle relaxants on the auditory cortical evoked potentials in humans( 1972)There are a number of studies on sensory information processing based on an analysis of cortical evoked potentials. Few studies however, provide direct evidence that the cortical evoked potentials are produced by neural generators in the brain. In fact, some research work has shown that most of the cortical evoked activity may be muscular in origin. (Bickford et al, 1964; Prichard et al, 1965). Consequently the present study was necessary as a preliminary to further research on sensory information processing in the auditory system.
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ItemField potentials in cat auditory nuclei in response to frequency and amplitude modulated sound( 1972)This study was undertaken to determine how the field potentials recorded from the cochlear nucleus, inferior colliculus, and primary and secondary auditory cortices varied for different modes of frequency and amplitude modulated sound. The sound was presented to anaesthetized animals as a burst of five consecutive modulation envelopes. It had modulation rates which varied from 10- to 80- Hz, and depths of 10%, 50% and 100%. The field potentials were summed over 63 stimulus presentations, and then a spectral analysis was carried out on the result. The evoked responses produced in the various nuclei and by different stimulus parameters were compared using a coherence function.