Visual allesthesia.

A patient with a right parietooccipital arteriovenous malformation experienced paroxysmal illusory left homonymous transpositions of objects viewed in the right homonymous field. The illusory images were palinoptic, persisting for up to 15 minutes after the real objects were no longer in view. She had left homonymous hemiachromatopsia and a right parietooccipital epileptogenic focus. Episodes of visual allesthesia were accompanied by other manifestations of seizures. Administration of anticonvulsant medications resulted in cessation of electroencephalographic epileptogenic activity and disappearance of all clinical manifestations of seizures, including visual allesthesias. Cerebral irritation and seizures, a defective but not blind half-field of vision, and experience of palinoptic images are essential components of some cases of visual allesthesia. The phenomenon may result from interhemispheric transfer of a visual percept from a normal to an irritated parietooccipital lobe, which then retains it as a palinoptic image.