Abstract: Recently, Task switching is an important paradigm for studying executive control. Switching cost refer to the performance differences in task-switch and task-repeat trials. Many issues and problems need further exploration. Theoretically, there is disagreement as to whether switch costs actually represents the task-set reconfiguration or the task-set inertia. Many studies have found that a prolonged preparation time reduces switch costs, which has been attributed to a task set reconfiguration process. However, unlike manipulations of preparation time, other studies have varied the predictability of task sequence and found that the preparation benefit was the same for switches and repetitions. The present study explored the interaction of preparation time and foreknowledge in task switching. In addition, in order to study the effects of preparation time predictability on the task switching, the preparation time (CSI) was manipulated by blocked or randomized within subjects.
Two explicit task-cuing experiments were used with the same materials and procedure, preparation times of 150ms and 900ms, and foreknowledge of the full- and the partial-foreknowledge. The full-foreknowledge specified both task transition and task identity. The partial-foreknowledge specified only task transition information. The response-stimulus interval was constant at 800ms, to control the amount of repetition priming from the previous trial. To examine the effect of preparation time predictability on the preparation effects of switch costs, in experiment 1, the preparation time was blocked within subjects, and in experiment 2, the preparation time was randomized within subjects. The RT was measured as the main index.
Repeated-measure ANOVA was performed for experiment 1 and 2. The results revealed that: (1) Under the conditions of preparation time predictability and unpredictability, the interaction between the preparation time and the foreknowledge was significant. Under the condition of predictability, the RT of repeat task and switch-to task trials decreased with increasing preparation time, but there are no significant differences of switch-to cost; the RT of switch-away task is affected by preparation time, and switch-away cost advanced with prolonging preparation time. Under the condition of unpredictability, the RT of three types of tasks reduced with rising preparation time, but both of switch-to and switch-away cost went up. (2) Compared to the switch-to task, the RT and switch cost of the switch-away task were longer. (3) Under of the two conditions, there is not the preparation effect. The experimental results suggest that the switch cost may represent the preparation of the new task set and a residual component, and the task switching was not effected by the predictability of the preparation time

Key words: executive control, task switching, switch cost, task set