Residual vision, or blindsight, following damage to the primary visual cortex was first identified almost a century ago. However, the mechanism and pathways underlying this ability, as well as the extent of visual function, remain unclear and are a continuing source of speculation. The work presented here goes some way to try to address these questions, investigating 18 patients with V1 damage and homonymous visual field loss acquired in adulthood. Six experimental chapters explore the extent and potential for visual function after V1 damage, and apply novel neuroimaging paradigms and techniques to try to uncover the mechanisms and pathways that might be involved. A combination of psychophysics, functional and structural MRI was used to investigate responses to blind field stimulation in the dorsal and ventral streams. In addition, diffusion MRI tractography was performed and related to psychophysical performance, so that the three main pathways implicated in blindsight could be evaluated. Lastly, a small rehabilitation study was carried out to assess the effect of training in the blind hemifield, and to investigate whether there is any transfer of learning between the dorsal and ventral visual streams. The results from this work reinforce the suggestion that blindsight may be more common than was first thought, and may extend across a number of characteristics involving both visual streams. It is also suggested that visual function need not be completely unconscious, but that certain salient stimuli can elicit both non-visual and crude visual experience. The use of parametric functional imaging paradigms has enabled a number of properties of non-striate inputs to the extrastriate cortex to be revealed. Together with tractography, this points to an important role for the ipsilateral lateral geniculate nucleus in blindsight function. It is hoped that future work will build upon this, and that it may be possible to target these residual pathways in the rehabilitation of patients with V1 damage.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:711927 |
| Date | January 2015 |
| Creators | Ajina, Sara |
| Contributors | Bridge, Holly ; Kennard, Christopher |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:2e274261-c71a-4ad1-82cf-2fe6bbdbf673 |
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