Abstract
OBJECTIVES: This study aims to specify the processing operations underlying age-related differences in the speed and accuracy of visual search in a mathematical model. METHOD: Eighteen older and 18 young adults searched for a predesignated target within 24-degree visual arrays containing distractors. Targets were systematically placed in regions that extended 2.5, 5.0, 7.5, and 10 degrees from center. Data were fitted to several versions of a mathematical model in which it was assumed that target search proceeds from the center fixation to peripheral areas in a succession of visual inspections of clusters until the target is located and that clusters can vary in size in response to search difficulty. RESULTS: Eccentricity effects on latencies and errors were larger for older adults than for younger adults, especially in the hardest search condition. The best-fitting version of the "search-by-clusters" model accounted for an average of 98.4% and 95.4% of the variance in the young and older adults, respectively. The resulting time, accuracy, and cluster parameters behaved plausibly in each of the 36 data sets. CONCLUSIONS: A quantitative model that specified how individuals searched for targets in large arrays accurately predicted the search times and accuracies of younger and older adults.