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Abstract:
Abstract: Patients with neglect may ignore the contralesional
part of space or ofobjects. Thus, neglect canoccur in a space-based
or an object-centered frame of reference. Weexamined whether
bothphenomena might be due to the same space-based deficit
modulated byattentional focussing.Neglect patients' eye movements
were recorded during three visual searchtasks. (1) Subjectssearched
for a target within a homogeneous stimulus array surroundingthe
subjects (+/-140° left andright of the body's mid-sagittal
plane). (2) Subjects explored the samearray which was nowsegmented
into areas (horizontal extension: 40°) differing in the colorof
their stimuli. (3) Subjectswere instructed to confine visual search
to one of the 40° segments ofthe array that was located inan
area from +40° to +80° on the right side. In the first and
the secondsearch task, all patientsneglected the left hemispace
demonstrating space-based neglect. Duringboth tasks, there
wasvirtually no left-right asymmetry in the area from +40° to
+80° on theright side. In contrast, allpatients completely
ignored the left part of this segment when they hadto concentrate
visual searchon this segment alone (task 3). The results suggest
that object-centeredeffects in neglect are due totask-dependent
focussing of attention arguing for its modulatoryinfluence on
egocentric spacerepresentation.
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