A model of visual search postulating that visuospatial attention is composed of two processing components-shifting and scaling of a variable-gradient attentional focus-was tested in three experiments. Whereas young participants are able to dynamically constrict or expand the focus of visuospatial attention on the basis of prior information, in healthy aging individuals visuospatial attention becomes a poorly focused beam, unable to be constricted around one array element. In the present work, we sought to examine predictions of this view in healthy young and older participants. An attentional focus constricted in response to an element-sized precue had the strongest facilitatory effect on visual search. However, this was true only when the precue correctly indicated the location of a target fixed in size. When precues incorrectly indicated target location or when target size varied, the optimal spatial scale of attention for search was larger, encompassing a number of array elements. Healthy aging altered the deployment of attentional scaling: The benefit of valid precues on search initially (in participants 65-74 years of age) was increased but later (in those 75-85 years of age) was reduced. The results also provided evidence that cue size effects are attentional, not strategic.This evidence is consistent with the proposed model of attentional scaling in visual search.
GREENWOOD AND PARASURAMANity between target and distractors. In contrast, under less demanding search conditions,such as those in which there are few distractors present or in which discrimination is easy, as in the phenomenon of popout, the optimal attentional focus would be a broader gradient. This enlarged and graded attentionalfocus may be better able to detect an easily discriminable target without the need for a saccade. An enlarged focus is also optimal when precues to target location are invalid-that is, located away from the target Greenwood, Parasuraman, & Alexander, 1997). Perhaps when the target appears at a distance, its properties can best be detected by a larger, more diffuse attentional focus. This view that visuospatial attention can be scaled flexibly reconciles the two dominant views of how visuospatial attention is deployed: a gradient (LaBerge, Brown, Carter, Bash, & Hartley, 1991) or a spotlight (Posner, 1980). Thus, the gradient that is characteristic of the attentional focus would be constricted to resemble a spotlight when arrays are large and discrimination difficult.This model also makes predictions about the effect of healthy aging on the deployment of visuospatial attention. The model claims that, in aging individuals,the attentional focus becomes a poorly focused beam, being both broader and less concentrated than that in young individuals. Furthermore, use of a poorly focused beam to locate targets increases dependence of the aging brain on such prior information as size and location cues. This heightened dependence is manifested as a greater effect of cue size on search speed in the young-old, as compared with yo...