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Title: The detection and discrimination of lateralised stimuli
Author: Davidoff, J. B.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1980
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A review of previous research reveals hemispheric differences in structure and function. While there may be classes of individual (e.g. sinistrals) who do not exhibit the normal division of function, in the majority are those for whom the left hemisphere is dominant for verbal and the right hemisphere dominant for non-verbal skills. This thesis concentrates on visual non-verbal tasks. The literature showed that an hemispheric superiority was more clear cut for what can be regarded as simpler tasks. A detailed analysis of the past work, including the author's work on brightness judgements, also showed that if the stimuli make for difficult discriminations then even basic perceptual tasks exhibit a right hemisphere superiority. This evidence comes from both clinical and normal populations and it would appear that the strength of this evidence has been underestimated. This thesis is devoted to showing that asymmetries can be reliably shown in normal subjects for the simple tasks of detection and discrimination. The visual half-field tachistoscopic methodology was used to achieve this aim. It is argued that previous work with normals using a reaction time paradigm did not always reveal a right hemisphere superiority because the tasks were not demanding. Experiment 1 reveals this to be the case and a clear asymmetry was shown. The asymmetry was not always present. Experiment 2 showed that a concurrent verbal task and presumably activation of the left hemisphere for stimulus reception did reduce the asymmetry but contrary to certain theories of hemispheric processing did not give a right visual field advantage. Sex differences were also seen to be related to visual field advantages,. Experiment 1 showed these to be more evident in male subjects; a conclusion verified in Experiment 5 but the difference was not as marked with both male and female subjects showing the asymmetry. The experimental work also delimited the nature of the lateral advantage. Experiments 3 and 4 showed tht the superiority was unlikely to be at the retina. Experiment 5, by using signal detection theory, ruled out response bias as the cause of the advantage.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available