Old age is associated with a pattern of relatively intact and relatively impaired task-set switching abilities

In three experiments, we examined the effects of old age on the reaction ti me (RT) decrement associated with task alternation. Old age was associated with increased miring-cost, which is the RT difference between two conditio ns: mired-task, where trials involving two tasks were intermixed, and singl e-task, where all the trials involved the same task. Old age was also assoc iated with an increased switching-cost, which is the RT difference between trials in which the task was just changed and trials in which it was repeat ed. There was also indication of a slowed passive dissipation of task set a dopted in the preceding trial. In contrast to these impairments, old age wa s also associated with an almost intact ability to prepare for an upcoming task switch. This ability was indicated by a normal reduction in switching- cost due to an increase in the time allowed to prepare for the switch. We d iscuss the implications of the results in relation to theories of task-swit ching and to the underlying brain mechanisms, especially with respect to th e effect of old age on the prefrontal cortex.