The objective is to investigate the changes in attention that occur during normal human aging. Participants will be college-age individuals and community-dwelling adults in their 60's and 70's. The two age groups will possess comparable levels of education. The experiments will examine adult age differences in the attentional demands of visual-search performance. The visual-search task requires subjects to make a choice response on the basis of a comparison between a set of target items (letters or digits) held in memory and a set of items presented in a visual display. Experiment 1 will investigate subjects' ability to perform both visual search and a secondary task, tone detection, concurrently. Measures of the proportional changes in dual-task tone detection and visual search, relative to their single-task baselines, will indicate whether age differences in search performance are best characterized as a generalized slowing in processing speed or as a reduction in the amount of effort available. Experiments 2 and 3 will examine the manner in which subjects use two modes of attention, focused and distributed, across the trial sequence. A model is proposed for how focused attention is shifted between target items held in memory, and the applicability of this model to young and older adults' search performance will be tested empirically. Experiment 4 will measure visual-search performance under a specified range of speed/accuracy conditions. This experiment will investigate age differences in the rate at which information is extracted from the visual display. In Experiments 5 and 6 the attentional demands of searching the display will be reduced by presenting the display items sequentially rather than simultaneously, and the effect of this presentation format on target identification and localization will be determined. Experiments 7 and 8 will provide advance information regarding the specific location of the target in the display. These two experiments will measure both the speed with which attention can be shifted across the display, independently of eye movements, and the potential influence of sensory processing on attentional shifts. The results are intended to improve current theories of age-related changes in cognitive function and to provide data that are relevant for rehabilitative and applied settings.