准备时间和预先信息对任务切换的影响

两个实验采用任务线索范式，考察了准备时间和预先信息对任务切换的影响。实验1的准备时间为可预测，实验2的为不可预测，以考察准备时间的可预测性对任务切换的影响。以被试执行重复任务、切到任务和切离任务的正确反应时为主要指标，结果：（1）在准备时间可预测和不可预测两种条件下，准备时间和预先信息之间存在显著交互作用。在可预测条件中，重复和切到任务的反应时随着准备时间的增加而减少，但切到代价无显著变化，切离任务的反应时不受准备时间的影响，切离代价表现出反准备效应；不可预测条件下，三种任务的反应时都随着准备时间的增加而减少，但是切到和切离代价表现出反准备效应；（2）切离任务的反应时和代价显著高于切到任务的反应时和代价；（3）在这两种条件下，都没有出现切换代价的准备效应

Effects of Preparation Time and Foreknowledge on Task Switching

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