Abstract: In task switching, switch cost is the performance differences in task-switch and task-repetition trials. Recently, some researches have attempted to specify nature and origins of switch cost to uncover the mechanisms underlying task switching performance. Theoretically, there is disagreement as to whether switch cost actually represents the task-set reconfiguration or the task-set inertia. Many studies 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 varied the predictability of task sequence and found that the preparation benefit was the same for switches and repetitions. The aim of the present study was to investigate the effect of foreknowledge and preparation time on task switching.
Two experiments were conducted in the present study. There were 30 participants (12 males and 18 females) volunteered to take part in experiment 1 and another 30 participants (9 males and 21 females) took part in experiment 2. In order to investigated the effect of foreknowledge on task switching, the experiment 1 was conducted with a 3 (foreknowledge type: no foreknowledge, part foreknowledge and full foreknowledge) × 2 (task type: switch task and repetition task) within-subject design. In the experiment 2, a 3 (preparation time: 100ms, 600ms and 1000ms) × 3 (foreknowledge type: no foreknowledge, part foreknowledge and full foreknowledge) × 2 (task type: switch task and repetition task) within-subject design was conducted to examined the mechanisms of effects of foreknowledge on task switching under the conditions of difference preparation time. The correct RT and switch cost were measured as the main index.
The results showed that: (1) the amount of switch cost depend on foreknowledge, switch cost was smaller with full foreknowledge than with part and no foreknowledge, but not difference significantly between the later two. (2) The interaction between preparation time and foreknowledge was significant, and with increased preparation time, the effect of foreknowledge was more remarkable.
Current findings suggest that the cognitive process that foreknowledge affected was task-set reconfiguration, rather than task-set inertia, and the effect was mediated by preparation time.

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