Axford, J G (1974) Human visual evoked potentials: a computer aided investigation into their origin and variability. Doctoral thesis, Keele University.

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Abstract

This thesis is concerned with the measurement of human visual Averaged Evoked Potentials (AEPs) to tachistoscopically presented pattern stimuli, i.e. the sudden appearance and disappearance of patterns into an otherwise;, continuously illuminated diffuse field, such that the overall change in luminance is zero or very small.
Previous work reviewed includes that on the response of single cells in the cat and monkey visual cortices to contoured stimuli, and also that on the measurement of human visual AEPs to patterned stimuli. The work of D.A. Jeffreys, indicating that AEP scalp distribution measurements showed promise for identifying source locations of the first two (temporally separate) pattern AEP components, is considered in detail.
The experimental apparatus and computing system are described, together with a detailed discussion of experimental errors.
The computing system was designed to be on-line and interactive, and a general discussion is included on the man-computer interface.
Four chapters report and discuss the experimental findings.
The first describes the adaptation effect of one stimulus on the AEP to another which follows it after a short time interval. The adaptation is plotted as a function of relative timings and pattern types. Monocular stimulation showed that the effect must be partially central in origin.
The second reports on variability of the AEP. The AEP standard deviation is plotted as a function of electrode position, and was found to be almost independent of the stimulus. A 'Running Average' technique is described for measuring longer term AEP variations.
The third describes a computerised AEP component separation method, which was developed and used to provide further confirmation that the two AEP components first identified by Jeffreys give scalp distributions compatible with dipole sources in the striate and extrastriate cortices. Four subjects were tested in detail, and the results compared with a simple dipole model.
The fourth describes the development and initial trials of an on-line Evoked Potential Stochastic Search Technique.
The results are discussed, and some confirmatory and extension experiments suggested.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry
Divisions: Faculty of Natural Sciences > School of Life Sciences
Depositing User: Lisa Bailey
Date Deposited: 05 Mar 2019 09:18
Last Modified: 05 Mar 2019 09:18
URI: http://eprints.keele.ac.uk/id/eprint/5999

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