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Title: Visual afterimages and their relation to central perceptual processes
Author: Davies, Peter
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1973
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The thesis is that, afterimages are conditionable which suggests some central component that may possibly contribute to normal perceptual stability by serving as a link between informationally rich, but discrete, perceptual samples and; classical conditioning may be a fundamental process n perception, possibly the physiological basis of Helmholtz's unconscious inference. The latter is the main theme of the thesis and has entailed the adoption of the Russian interpretation of classical conditioning which does not exclude consciousness in the way that American interpretations have done in the past. Although this theme is illustrated in the main by the above experiments, other behavioural evidence, reinterpretations of previous experiments, and by the incorporation of previous theories it does have some indirect physiological support. There is a considerable amount of evidence derived from evoked potential studies and work with implanted electrodes that the visual system of mammals contains the required neuronal structures. The existence of 'on-off' detectors, Movement detectors, and feature specific detectors at the retinal level is well documented. Baumgarten and Jung (1952) identified five types of cortical neuron with, distinctive firing patterns following visual stimulation. Grusser and Grutansr (1958) correlated the firing patterns of retinal 'on - off' receptors and cortical neurons in the cat with the subjective visual afterimages of man. The results suggest that the peripheral receptors respond only during the initial stimulation and for 300 milliseconds thereafter. The Response at this level is maximal during the Hering afterimage and is approaching base level with the off-set of the Parkinje afterimage. The Hess after-image and all subsequent stages correlate well only with the firing patterns of the five types of cortical neuron. This study is based upon a cross-species correlation so we may not say that these time relations exist in man but when taken with the evidence from conditioning it seems likely that the later after- images may play some part in normal perception. Appropriate central structures exist, they may respond to a signal stimulus following a deliberate conditioning procedure, and such responding would account for those features of the visual afterimage that the traditional view does not account for. The possibility of linkage between these structures and verbal stimuli was demonstrated in the pilot studies of pre- and second-order conditioning and it is believed that this may be relatable to theories asserting a more general cognitive participation in the process of perception.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available