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Abstract:
Previously, we have used stabilized field mapping techniques
to investigate residual visual abilities in hemianopic subjects.
Two hemispherectomized subjects demonstrated limited detection and
discrimination abilities within their blind fields (Wessinger et
al., 1996). Generally, these abilities were restricted to regions
along the vertical meridian extending less than 6° into the
field defect and were accompanied by phenomenal awareness, Such a
pattern of results is most consistent with an explanation based on
naso-temporal overlap. More extensive patterns of residual vision
have been found in other patients. More specifically, seven
subjects hemianopic subsequent to stroke, demonstrated a similar
pattern of phenomenal residual vision along the vertical meridian.
More importantly, four of these subjects also demonstrated
"islands" of vision without awareness at isolated locations within
their field defects (Wessinger, et al., 1998). Given different
subjects demonstrated different abilities at different locations,
these data are most consistent with the notion that residual vision
is mediated by remnants of the primary visual pathway. We now
report data from additional subjects currently undergoing
stabilized field mapping. One subject (MO) demonstrates an
irregular pattern of vision along the vertical meridian extending
beyond 6° into her field defect. Interestingly, her visual
awareness decreases as stimulus eccentricity increases. Such
results have implications for understanding visual awareness and
blindsight.
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