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Abstract:
Abstract: Spatial localization is commonly used as a
screening test for "blindsight" in hemianopes with damage to
striate cortex. We tested a 46 year old patient, D.C., who had
undergone a left occipital lobectomy for the treatment of epilepsy
seven years previously. Targets were flashed on briefly at four
locations along the horizontal meridian of the patient's blind
(right) visual field. Following the target and a tone, the patient
was instructed to saccade and point to one of four marked locations
where the target had appeared. D.C. consistently selected the
mirror-symmetric location; for example, when the most eccentric
target was flashed, she indicated the location closest to the fovea
and vice versa. The patient's performance fell to chance when the
experiment was repeated with the blind hemifield occluded, ruling
out extraocular light scatter as an explanation for these results.
D.C. reported highest confidence for the most eccentric targets;
however, this was true whether or not the blind field was occluded,
suggesting that subjective experience was unrelated to her
performance. These results suggest that D.C. has reliable access to
a spatial map within her blind visual field, albeit a
misrepresented one. Further behavioural and neuroimaging tests will
address the nature of the misrepresentation.
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