Executive control of cognitive processes in task switching

In 4 experiments, participants alternated between different tasks or perfor med the same task repeatedly. The tasks for 2 of the experiments required r esponding to geometric objects in terms of alternative classification rules , and the tasks for the other 2 experiments required solving arithmetic pro blems in terms of alternative numerical operations. Performance was measure d as a function of whether the tasks were familiar or unfamiliar, the rules were simple or complex, and visual cues were present or absent about which tasks should be performed. Task alternation yielded switching-time costs t hat increased with rule complexity but decreased with task cuing. These fac tor effects were additive, supporting a model of executive control that has goal-shifting and rule-activation stages for task switching. It appears th at rule activation takes more time for switching from familiar to unfamilia r tasks than for switching in the opposite direction.