ABSTRACT
One of the best exemplars of a mental activity in which large and robust age-related differences have been consistently obtained is dual-task processing. In dual-task or divided attention paradigms subjects are instructed to concurrently perform two tasks. In some varieties of this paradigm subjects are instructed to treat one task as primary and the other task as secondary. In other situations subjects are instructed to treat the tasks as equally important. Dual-task “costs” are assessed by comparing performance of each of the tasks when performed together to their respective single task control conditions. The dual-task decrements have been calculated as both absolute costs (e.g., dual-task performance minus single-task performance) and relative costs ([dual minus single] divided by single). In both cases, the decrement measures represent an attempt to employ the single task conditions as baselines against which to compare dual-task performance. In situations in which reaction time (RT) serves as the dependent measure, relative cost measures are more conservative estimates of age differences in dual-task performance given that older subjects tend to respond more slowly than younger subjects on single tasks (Guttentag, 1989; Somberg & Salthouse, 1982; but see Ackerman, Schneider, & Wickens, 1984; Baron & Mattila, 1989). In general, the study of dual-task processing in the laboratory represents an attempt to understand the manner in which humans cope with processing demands inherent in many real-world situations such as driving an automobile, cooking dinner while carrying on a telephone conversation, typing a manuscript while composing a letter, walking down a flight of stairs while planning a meeting, and so on. In fact, there have been a number of studies that have found that performance in divided attention and attention switching tasks is predictive of the quality of real-world performance in tasks such as flying an aircraft (Crosby & Parkinson, 1979; Damos, 1978; Gopher, 1982; North & Gopher, 1976), driving buses (Kahneman, Ben-Ishai, & Lotan, 1973) and automobiles (Avolio, Kroeck, & Panek, 1985; Ball & Owsley, 1991).
