Controlling the focus of spatial attention during visual search: effects of advanced aging and Alzheimer disease.

It was hypothesized that slowed visual search in healthy adult aging arises from reduced ability to adjust the size of the attentional focus. A novel, cued-visual search task manipulated the scale of spatial attention in a complex field in healthy elderly individuals and patients with dementia of the Alzheimer type (DAT). Precues indicated with varying validity the size and location of the area to be searched. Location precues exerted the strongest effects on conjunction search and the weakest effects on feature search. As the size of valid location cues decreased, conjunction search was facilitated. These effects declined progressively with advanced age and the onset of DAT. As the size of invalid cues increased, conjunction search was first facilitated, then slowed, but neither age nor DAT altered this effect. These results indicate that both Alzheimer's disease and, to a lesser degree, advanced aging, reduce control of the spatial focus of attention.