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Scanning the visual world: a study of patients with homonymous hemianopia
Abstract
OBJECTIVES—This study
examined the scanpaths of patients with homonymous hemianopia while
viewing naturalistic pictures in their original and also spatially
filtered forms. Features of their scanpaths with respect to various
saccade and fixation parameters were examined to determine whether they
develop compensatory eye movement strategies. The effects of various
lesion parameters including location, size, and age on the evolution of
such strategies were considered.
METHODS—Eye movements
of eight patients with homonymous hemianopia (four left, four right),
but lacking neglect, were recorded while they viewed 22 images of real
scenes, and they were compared with the eye movements of eight age
matched controls. Subjects viewed each image for 3 seconds, initially
in a spatially filtered form in which much of the semantic content had
been removed, and then in their unfiltered, original form.
RESULTS—Patients
differed significantly from controls in various fixation and saccade
parameters. For fixation parameters patients with hemianopia fixated
different spatial positions from controls, made more fixations which
were more widely distributed and of shorter duration than controls, and
spent a greater proportion of their total fixation time in the area
corresponding to their blind hemifield. They did not make significantly
more refixations than controls. For saccade parameters patients made
more saccades into their blind hemifield, these saccades having shorter
latencies and shorter amplitudes than those made into their seeing
field, and had longer scanpaths than control subjects. The amplitude of
their first saccade was longer than that of controls although its
direction did not correlate simply with the side of the field defect.
Their mean saccade amplitude was similar to that of controls. Filtering
out high spatial frequencies within images seemed to accentuate the
described differences between eye movement characteristics of
hemianopes and controls. Scanpath differences correlated with increasing age but not location or size of lesions causing the hemianopia.
CONCLUSION—Various
features of scanpaths produced by hemianopes were different from normal
subjects. These differences correlated with lesion age and may reflect
the evolution of a compensatory eye movement strategy.
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Selected References
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