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Diego Fernandez-Duque, Sandra E Black; Visuo-perceptual abilities in patients with atypical Alzheimer's Disease. Journal of Vision 2003;3(9):593. doi: 10.1167/3.9.593.
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© ARVO (1962-2015); The Authors (2016-present)
We tested the spatial attention and visuo-perceptual abilities of two patients with atypical Alzheimer's disease. Neuroimaging revealed hypoperfusion in parietal, posterior temporal, and lateral occipital cortex. In patient R.D, who exhibited neglect and extinction, hypoperfusion was lateralized to the right hemisphere. In patient M.M., who had no spatial neglect, hypoperfusion was left lateralized. Both patients were impaired in the copying and matching of simple shapes, but recognition of more complex figures was relatively preserved. A 2-AFC task assessed the patients' ability to perceive two objects at the same time. In this task, two concentric figures (e.g., a circle and a square) were briefly displayed. When the figures were displayed sequentially, patients correctly reported whether the shapes were the same (e.g., two circles), or not (e.g., a circle and a square). In contrast, performance was close to chance when the figures were displayed simulatenously. This simultanagnosia may stem from a deficit in spatial attention. To explore this possibility, in a follow-up study two concentric figures were displayed, and patients had to report the shape of one of them (i.e., the target). In separate blocks, the feature that defined the target was either spatial (e.g., the ‘large’ figure) or non-spatial (e.g., the ‘black’ figure). Spatial cues led to more accurate performance than non-spatial cues. This result is consistent with an attentional account of simultanagnosia, by which patients can attend to a selected stimulus, but have difficulties disengaging from it.
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