Visual Space Across Eye Movements: Studies in Normals and Patients with Unilateral Spatial Neglect.

Mrs Marilia Libera (). Visual Space Across Eye Movements: Studies in Normals and Patients with Unilateral Spatial Neglect. Professional Doctorate, School of Psychology, The University of Queensland.

       
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Author Mrs Marilia Libera
Thesis Title Visual Space Across Eye Movements: Studies in Normals and Patients with Unilateral Spatial Neglect.
School, Centre or Institute School of Psychology
Institution The University of Queensland
Thesis type Professional Doctorate
Supervisor Prof. Jason Mattingley
Dr. Ranmalee Eramudugolla
Total pages 140
Abstract/Summary Every time we move our eyes, visual information about fixed objects in the world falls on different parts of the retina. Despite these constant changes in the retinal image, however, we perceive the world as stable and continuous. It is assumed that visual stability is achieved through the process of spatial updating, which refers to the updating of neural representations of space across eye movements. Evidence from neurophysiological studies in both non-human primates and humans has associated regions of the posterior parietal cortex with this process. Based on the known specialisation of the right hemisphere in processing spatial information, it is suggested that this asymmetry may also hold for spatial updating processes. This raises the question of how spatial updating processes might be affected when areas of the right parietal cortex are damaged, as is often seen in patients with the syndrome of unilateral spatial neglect. Patients with spatial neglect ignore the contralesional side of the world, due to pathological inattention, even in the absence of any sensory defects. The current project aimed to investigate whether right-hemisphere lesion patients with neglect have spatial updating impairments, and if so whether impairments show an asymmetry for leftward versus rightward eye movements. Memory for a target (Updating Locations, N = 11 patients; or Updating Objects, N = 8 patients) was probed after patients executed an eye movement across the midline from initial fixation (remapping condition). Target and probe were always presented in opposite hemifields. In the control task both target and probe were presented centrally (‘no remapping’). There was substantial heterogeneity in patients’ performances. Two patients, however, showed a distinct asymmetry with worse performance after leftward gaze shifts. Also, overall, memory for object features was worse than for object locations. To further investigate spatial remapping, the current project also explored how spatial attention is deployed immediately following an eye movement. This was done by exploring remapping mechanisms in a population of neurologically healthy individuals (N=13. Specifically, remapping of the attentional spotlight was investigated in terms of retinotopic versus spatiotopic representations. The second experiment (N=13) used a novel paradigm that combined a spatial cueing procedure with guided gaze shifts. Participants made a right/left judgment regarding the location of a probe that followed either a valid or invalid cue presented before an eye movement and either to the opposite (‘spatiotopic’) or same hemifield (‘retinotopic’). Responses were faster after a valid cue in both conditions, with a trend for faster responses when remapping in spatiotopic coordinates. The present findings demonstrate that in the normal brain the concept of updating spatial representations extends to the updating of the focus of spatial attention, which allows us to keep track of attended locations across eye movements. In contrast, with damage to the right hemisphere, this ability is impaired. As spatial attention is disrupted across eye movements, patients with neglect display difficulties in remembering both the location and features of objects that they have just attended prior to an eye movement. Thus, with an eye movement, previously attended locations and objects tend to escape awareness, a hallmark of the neglect disorder.
Keyword Visual
spatial attention
unilateral spatial neglect
eye movments
Saccades

 
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Created: Wed, 27 Oct 2010, 00:12:29 EST by Mrs Marilia Libera