Brain : a journal of neurology
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Thirteen patients with transient or permanent homonymous visual field defects experienced formed hallucinations localized to the affected part of the visual field. The lesion was occipital in 8 instances (infarction 7, porencephalic cyst 1), parietooccipital in 3 (infarction 2, angioma 1) and probably parietal in 2 (epilepsy 1, encephalitis 1). The disorder involved the right hemisphere in 9 cases, the left hemisphere in 3 cases and both hemispheres sequentially in one patient. ⋯ In most cases, the hallucinations were not clearly related to any visual memory. It is suggested that the visual association cortex amy be responsible for the organization of visual percepts into broad categories of which people, animals and objects are representative. The occurrence of such hallucinations with a visual field defect suggests that the cells of the association cortex are more likely to discharge spontaneously once they are deprived of their normal afferent inflow from the calcarine cortex.