Looking but not seeing: attention, perception, and eye movements in simultanagnosia.

We studied three subjects who reported the apparent "disappearance" of stationary objects from direct view. They had simultanagnosia caused by CT-verified bilateral superior occipital lobe lesions. They had no abnormalities of visual acuity or fields to explain their defect. EOG with computer analysis showed intact motility and scanning. Most important, the subjects reported intermittent disappearance of a light target during EOG-verified fixation--ie, they were looking but not seeing. Results indicate that attention mechanisms that permit sustained awareness of visual targets depend on the superior visual association cortices and are relatively separate from mechanisms that shift gaze and drive visual search.