Attention Orienting System and Associated Disorders

Neglect, Extinction and Balint’s Syndrome

Orienting Spatial Attention

• Corbetta et al. (1993)

– Subjects oriented attention according to a light moving in the visual field

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

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?

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)

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

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

Hemispatial Neglect

• E.g. line bisection task

Hemispatial Neglect

• E.g. reproducing visual forms

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

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

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

Balint’s Syndrome