Alzheimer disease constricts the dynamic range of spatial attention in visual search

A cued visual search task was used to examine the dynamic range over which spatial attention affects target identification during visual search. Precu es varied in validity (valid, invalid, or neutral) and in precision (cue si ze) of target localization. Participants were "young-old" (65-74 years) and "old-old" (75-85 years) elderly adults and individuals in the mild stage o f dementia of the Alzheimer type (DAT). For all participants. search was sp eeded us the precision with which a precue surrounding the location of a su bsequently appearing target increased (precue size decreased). The cue size effect was evident in both feature and conjunction search. but was greatly reduced in both old-old and DAT groups compared to the young-old. However, whereas all non-demented adults showed a progressive modulation of search efficiency over the entire range of cue sizes, the dynamic range of spatial attention was restricted to the most precise cue in the DAT group. The res triction in the dynamic range of spatial attention may represent an underly ing component of the impairment in perceptual and memory functioning found in early-stage DAT. (C) 2000 Elsevier Science Ltd. All rights reserved.