Narrowing the Spotlight: A Visual Attentional Disorder in Presumed Alzheimer's Disease

Visuo-spatlal dysfunction is the initial and most disabling Impairment in a small proportion of patients with progressive dementia. We report a series of investigations of two patients with probable Alzheimer's disease (AD) in which progressive visuospatial deficits dominated the clinical picture. Both patients exhibited substantial impairments on a visual search task and read words printed in small letters better than words printed in large letters. When stimuli were presented in which a large letter was composed of small letters (e.g. an ‘S’ composed of ‘T's), the patients identified the small letter faster and more reliably. These and other data are consistent with the hypothesis that the patients exhibit a restriction in the capacity of the spotlight of visual attention.