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In a prospective study of 32 consecutive patients with homonymous visual field defects due to ischemic infarcts we found hemianopic anosognosia (HAN),defined as the unawareness of visual loss in the homonymous hemifield(or hemiquadrant),in 20 patients(62%).HAN,although occurring predominantly in the right-sided lesions in 16 of 26 patients(62%)was also present in four of six patients,or(67%)with left-sided lesions.This group of patients has been presented in a prior report on positive spontaneous visual phenomena.HAN was associated with somatic anosognosia in nine patients and hemineglect in 17 patients.Dissociation between somatic anosognosia,as well as between hemineglect and HAN,was present in several patients,indicating that these phenomena may be independent of each other. Eight patients had pure homonymous hemianopia,that is,hemianopia without cognitive,motor or somatosensory deficits.Four of these patients(Group A) had awareness of the visual deficit,whereas three patients(Group B)had HAN.Patients in these two groups had similar anatomic lesions.We suggests that HAN is most often related to failure of discovery of the deficits occasionally to severe hemineglect,sometimes to generalized cognitive impairment,or to a combination of these factors.We further conclude(1)that there is no specific cortical area for conscious visual perception;(2) visual awareness is processed by a distributed network including multiple visual cortices,parietal and frontal lobes,the pulvinar and the lateral geniculate bodies(lesions localized at various nodes or centers in the network may produce similar phenomena;and(3)both hemispheres are involved in visual processing and conscious awareness. |
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agnosia
agnosia,hemianopic
CAT scan
CAT scan,abnormal
cerebral infarction
cerebrovascular accident
hemianopia
hemianopia,homonymous
visual field defect
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