attention orienting system and associated disorders neglect, extinction and balint’s syndrome
Post on 19-Dec-2015
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Attention Orienting System and Associated Disorders
Neglect, Extinction and Balint’s Syndrome
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Orienting Spatial Attention
• Corbetta et al. (1993)
– Subjects oriented attention according to a light moving in the visual field
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Orienting Spatial Attention
• Results:
– Parietal and Pre-motor areas were activated by attention tracking task
– Hemisphere of activation depended on which visual field attention was being shifted in
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Orienting Spatial Attention• Corbetta et al (1993)
confounded stimulus w/ orienting
• Hopfinger et al. (2000) used event-related fMRI to identify top-down orienting processes (distinct from stimulus-driven processes)– Cue-target paradigm using
arrows– What is the brain activity
caused by the cue?
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Orienting Spatial Attention
• Result:– Cue-related activations indicate a distributed network that mediates
voluntary orienting
– Network includes mainly frontal and parietal structures, mainly on the left side (keep this in mind for discussing neglect)
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Orienting Spatial Attention
• Result:– Directly contrasting
cue vs. target reveals an attention orienting network distinct from a target processing network
Cue activity > Target activity Target activity > Cue activity
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Hemispatial Neglect
• Unilateral lesion to Parietal or Temporo-Parietal Junction
• Patients present with vision problems, but are not “blind”– Rather, they fail to
apprehend (and interact appropriately with) stimuli in the contralesional field
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Hemispatial Neglect
• E.g. line bisection task
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Hemispatial Neglect
• E.g. reproducing visual forms
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Investigation of Neglect with Cue-Target Paradigm
• Posner et al. (late 1970s) used a cue-target paradigm
• Parietal Lobe patients are profoundly impaired only when invalidly cued to attended to the ipsilesional (good) side
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Extinction
• Extinction is a more complicated aspect of neglect• Patients fail to apprehend objects in the
contralesional field when stimuli are present in the ipsilesional field
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Balint’s Syndrome
• Bilateral parietal lesions
• Patients fail to apprehend all but one of simultaneously presented objects at the same location
• Condition is object-based, not location-based– Multi-colored dots are
properly seen if they are connected by lines
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Balint’s Syndrome