Redundancy Gain in the Absence of the Corpus Callosum

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dc.contributor.advisor Corballis, Michael en Roser, Matthew en 2007-07-07T08:33:09Z en 2007-07-07T08:33:09Z en 2001 en
dc.identifier THESIS 02-107 en
dc.identifier.citation Thesis (PhD--Psychology)--University of Auckland, 2001 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract This thesis examines interhemispheric interaction in the absence of the corpus callosum. Reaction times (RTs) to single luminant stimuli presented in each visual field, were compared to RTs to bilateral redundant-stimuli pairs. This was done in four subjects in whom the cortical commissures had been cut, two subjects with agenesis of the corpus callosum and fourteen neurologically normal controls. This comparison allowed for the calculation of the redundancy gain, or the degree to which responses to bilateral redundant-stimuli pairs were faster than responses to single stimuli. The first experiment manipulated stimulus location in a simple RT task. This allowed the effects of stimulus eccentricity and stimulus midline symmetry to be gauged. RTs were found to be fastest to bilateral redundant-stimuli pairs for all the split-brained or acallosal subjects, and for the control group, constituting evidence for a redundancy gain. The redundancy gain was found to be too large to be accounted for as the probabilistic outcome of a "race" between independent processes, implying neural summation. Paradoxically, the evidence for neural summation with bilateral redundant-stimuli was greatest in those subjects in whom the cortical commissures were disrupted. Neural summation was not greatly affected by stimulus symmetry, and this was taken as evidence against the hypothesis that the effect involved the convergence of perceptual activation at the superior colliculus. The second experiment involved responding to stimuli that could be either red or green. Redundant-stimuli pairs could be either of same, or of different, colour. This allowed the effect of colour difference on the redundancy gain to be determined, and also served as a control task for the third experiment. Neural summation was found to be equally evident for same or different colour pairs. The third experiment used the same stimuli as the second experiment, but responses were only to be made to stimuli of target colour. It was found that, while redundant-target stimuli produced a robust redundancy gain, indicating neural summation, redundant-stimuli pairs which consisted of a target stimulus paired with a nontarget stimulus, did not. The conclusion was drawn that neural summation depends on the convergence of redundant response processes from each hemisphere, probably involving cortico-cerebellar motor loops. The effect was most evident in the split brain because, only when bilateral redundant target stimuli were presented were both hemispheres involved in preparing a response. Callosal transmission in neurologically normal subjects, and transmission via compensatory pathways in the subjects with agenesis of the corpus callosum, may have reduced the redundancy gain. en
dc.language.iso en en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA99101288214002091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated en
dc.rights Restricted Item. Available to authenticated members of The University of Auckland. en
dc.rights.uri en
dc.title Redundancy Gain in the Absence of the Corpus Callosum en
dc.type Thesis en Psychology en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The author en

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