Selective impairment of spatial attention during visual search in Alzheimer's disease.

Spatial attention during visual search was examined in 14 persons with mild Alzheimer's disease (AD) and 28 healthy older subjects, 14 aged 65-74 (young-old), and 14 aged 75-85 (old-old). Subjects searched for single feature (color) or conjunction (color + letter) targets in displays of 10 or 15 letters. Precues of differing sizes were used to provide localizing information of varying precision. Effects of display size and cue size on reaction time (RT) for color search were similar in AD subjects and controls. For color + letter search, however, AD patients showed minimal effects of cue size, pointing to an impairment in AD in the spatial focusing of attention during visual search. Pathology affecting the association parietal and extrastriate areas may mediate impairment of spatial attention and visual search in AD.