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Abstract:
We examined the status of visual processes subserved by
dorsal and ventral systems in a patient with dorsal system damage.
B. W. sustained extensive bilateral damage to occipito-parietal
cortex following removal of a tumor. By contrast, ventral
occipito-temporal cortical areas were relatively spared.
As expected, B. W. is deficient in tasks for which dorsal
structures are required: he shows some impairment in stereo fusion;
has elevated discrimination thresholds in a shape-from-shear
version of the Efron Squares task; and is impaired at identifying
objects defined by motion contrast.
Also as expected, B. W. performed within normal range on a number
of tests assessing processes mediated by ventral system structures.
He can perform the Warrington and James (VOSP, 1991) silhouette
identification, object decision, and fragmented letters tasks and
he can discriminate between drawings of possible and impossible
animals (Riddoch & Humphreys, 1987).
Intriguingly, he performed poorly on an object decision task that
required discrimination between possible and impossible geometric
objects (Schacter et al, 1990); he failed to show effects of
priming on the perception of degraded figures; and he was impaired
at recognizing objects depicted under occlusion in figure-ground
displays.
These results suggest that dorsal stream structures play a role in
these object perception tasks.
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