The literature on divided attention and adult aging has not taken age differences in single-task performance into account, and it has not been able to measure divided attention independently of resource allocation strategies. Two experiments are reported that,controlled for these factors. In the first experiment, young (I 8-23 years) and old (57-76 years) subjects made respon3es to two simultaneous visual displays. Stimulus durations were manipulated to equate single-task performances, and across different conditions subjects were induced to vary the way in which they allocated resources between the two displays. In the second experiment, respons€ time was the dependent variable; dual-task scores were assessed relative to each subject's single-task scores. No significant age difference in divided attention ability independent of single-task performance level was found in either experiment. The existing literature must be reexamined in light of these issues.

SUMMARYDespite a general neglect in contemporary research of the role of practice on the performance of simple components of skill, considerable evidence indicates that experience leads to substantial improvement in detection, discrimination, ani speeded classification. One goal of the present research was to identify the mechanisms responsible for practice-related improvement in such elementary tasks. A second goal was to determine whether there are adult age differences in the magnitude of practicerelated improvement on simple perceptual and cognitive skills or in the mechanisms used to achieve that improvement.Eight young adults (ages 19 to 27 years) and 8 older adults (ages 62 to 73 years) performed four simple tasks for 5l experimental sessions. On several sessions the subjects received qualitatively or quantitatively different stimuli to determine the mechanisms responsible for improvement. A concurrent reaction-time task was also performed at three different periods to assess the level of residual capacity after various amounts of practice.The results were interpreted as suggesting that improvement is due to shifts in the type of information being processed, in the identity or sequence of processing operations, and in the attention requirements of the task. A model incorporating these mechanisms is proposed and its application to the data is discussed.Age differences persisted on nearly every performance measure throughout all levels of practice. Moreover, there was little evidence that young and old subjects were qualitatively different in the manner in which they performed the tasks. It is suggested that the major difference between young and old adults on simple perceptual and cognitive tasks is the rate of processing nearly all types of information.Skill generally refers to the possession of expertise in some fairly complex, temporally interrelated behavior. For example, a skilled typist or pianist has a well coordinated sequence of manual keystrokes; the development of that coordination is probably the major part of skill acquisition in these domains, because the keystrokes themselves are extremely simple in isolation. However, in other areas of skill it is possible that performance of each individual component changes with increasing expertise. Perhaps substantial improvements do not occur in the quality of a simple keystroke, but other perceptual or motoric aspects of skill might improve independent of the overall coordinated integration of the components.Consider the case of drivine an automobile. Driving involves a complex coordinated sequence of perceptual and motor activities, and the skilled driver almost certainly possesses a more efficient integration and coordination of these activities than the novice driver. The expert is probably better able to turn the steering wheel while applying pressure to the brake or accelerator, to engage the clutch with his or her foot while manually shifting gears, to sound the horn while applying pressure to the brakes, and so on. One could also ask. however, ...

The 'locus' of the age-associated behavioral slowing was investigated with Sternberg's additive-factor method of identifying information processing stages. The factor of adult age was found to interact with manipulations assumed to influence stages concerned with stimulus encoding, internal comparison, and response preparation or execution. Since age appeared to affect each stage of information processing, it was suggested that the age-associated slowing phenomenon is general rather than specific.

The relationships between reaction time and classification accuracy were compared in young (18 to 21 years) and old (60 to 84 years) adults in a choice reaction time task. Both young and older adults showed equivalent rates of increasing accuracy with greater time, but the temporal duration at which the accuracy first exceeded the chance level was shorter for young than for older adults. It was suggested that aging is associated with a slowing of the information integration and/or response preparation processes but not with a slowing of the actual rate of information extraction.

to the first author. We wish to thank J. Mueller for his comments on an earlier draft.Requests for reprints should be sent to Timothy A.