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One month after a stroke, Fellini's left neglect is apparent when copying a Rey-Osterrieth Complex Figure (A) and then drawing it from memory 10 minutes later (B), showing a rather poor memory performance and an "imaginative spontaneous production" on the right side.
Another perceptual disorder, hemispatial neglect, is an agnosialike disorder resulting from damage to the right parietal lobe, a multimodal association cortex in which our concept of space is generated. Typically resulting from a stroke, acutely affected patients fail to recognize the left side of space even to the point of failing to recognize the left side of their own body. Sculptors may omit the left half of a head, even when the clay they are sculpting is on a rotating platform. The Italian film director Federico Fellini, who was also a cartoonist, developed left hemineglect after a right hemisphere stroke, and his cartoons reflected this, showing details clustered on the right side of the page with a paucity on the left (Cortex 1998;34:163-89).
Individuals with conversion disorders may state that they are unable to see or hear or feel, but some disorders that appear to be psychogenic are anything but. Balint’s syndrome, which is characterized by simultanagnosia as well as ocular apraxia and optic ataxia, was originally termed "psychic blindness." Simultanagnosia results from bilateral parieto-occipital lesions and can result from stroke, trauma, or degenerative brain disease (for example, visual variant Alzheimer’s disease) most commonly. Patients fail to see objects in plain view, yet when formally tested, have normal visual acuity leading early clinicians and many current-day ophthalmologists to conclude incorrectly that their visual impairment must be psychogenic. Such individuals also typically have severe constructional apraxia that obviously impairs any artistic expression requiring visuospatial or constructional skills.
All of these conditions impair our primary or secondary levels of perception, but next month, we will extend this further into the realm of mental imagery.
Dr. Caselli is medical editor of Clinical Neurology News and is a professor of neurology at the Mayo Clinic in Scottsdale, Ariz. This column, "Evoked Potentials," appears regularly in Clinical Neurology News, a publication of Elsevier.