title: Simultanagnosia: a defect of sustained attention yields insights on visual information processing.
abstract: Simultanagnosia, in which subjects report a piecemeal visual experience, offers an important probe of human attention. We studied 2 subjects with simultanagnosia following bilateral superior occipital strokes. Compared with controls, they could orient attention to spatial targets in visual, auditory, and mixed-modal conditions. A different task required immediate response to the appearance or disappearance at unpredictable intervals of any element in a random-dot CRT display. The subject tested could detect less than 50% of 1,600 events, and had increased "mirages" and prolonged reaction times. Undetected events occurred anywhere and formed temporal clusters. Application of signal-detection theory confirmed abnormal sensitivity and response bias (d' and beta). Yet performance improved when a valid cue introduced events in the random display. Our results suggest that simultanagnosia was related to an inability to sustain visuospatial attention across an array, corresponding to processing failure at a level of long-range (global) spatiotemporal interactions among converging inputs from early vision. The operations for orienting and sustaining attention may be dissociable at visual association cortex levels.
authors.affiliation: Department of Neurology, College of Medicine, University of Iowa, Iowa City.
authors.forename: M
authors.initials: M
authors.lastname: Rizzo
authors.forename: D A
authors.initials: DA
authors.lastname: Robin
mesh_terms: D000328:Adult; D000368:Aged; D000377:Agnosia / Q000503:physiopathology*; D000704:Analysis of Variance; D001288:Attention; D003072:Cognition Disorders / Q000503:physiopathology; D004585:Electrooculography; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D013028:Space Perception; D014057:Tomography, X-Ray Computed; D014793:Visual Cortex / Q000000981:diagnostic imaging / Q000473:pathology; D014796:Visual Perception