Kübler Sebastian, Reimer Christina B, Strobach Tilo, Schubert Torsten
Department of Psychology, Humboldt-Universität zu Berlin, Berlin, Germany.
Department of Psychology, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany.
Psychol Res. 2018 Jan;82(1):40-53. doi: 10.1007/s00426-017-0910-6. Epub 2017 Aug 30.
Dual tasks (DTs) are characterized by the requirement for additional mechanisms that coordinate the processing order of two temporally overlapping tasks. These mechanisms are indicated by two types of costs that occur when comparing DT blocks with fixed and random orders of the component tasks. On a block level, task-order control costs are reflected in increased reaction times (RTs) in random-order compared to fixed-order blocks, indicating global, monitoring-based, coordination mechanisms. On a trial level, within random-order blocks, order-switch costs are indicated by increased RTs on order switch compared to order repetition trials, reflecting memory-based mechanisms that guide task-order in DTs. To test the nature of these mechanisms in two experiments, participants performed DTs in fixed- and random-order blocks. In random-order blocks, participants were either instructed to respond to both tasks according to the order of task presentation (sequential-order instruction) or instructed to freely decide in which order to perform both tasks (free-order instruction). As a result of both experiments, we demonstrated that task-order control costs were reduced under the free-order compared to the sequential-order instruction, whereas order-switch costs were not affected by our instruction manipulation. This pattern of results suggests that the task-order control costs reflect global processes of task-order regulation such as engaging monitoring processes that are sensitive to changes in order instructions, while order-switch costs reflect rather local memory-based mechanisms that occur irrespective of any effort to coordinate task-order.
双重任务（DTs）的特点是需要额外的机制来协调两个时间上重叠任务的处理顺序。当将DT块与组成任务的固定顺序和随机顺序进行比较时出现的两种类型的成本表明了这些机制。在块层面，与固定顺序块相比，随机顺序下反应时间（RTs）增加反映了任务顺序控制成本，这表明存在基于全局监测的协调机制。在试验层面，在随机顺序块内，与顺序重复试验相比，顺序切换时RTs增加表明了顺序切换成本，反映了在DTs中指导任务顺序的基于记忆的机制。为了在两个实验中测试这些机制的性质，参与者在固定顺序和随机顺序块中执行DTs。在随机顺序块中，参与者要么被指示根据任务呈现的顺序对两个任务做出反应（顺序指令），要么被指示自由决定以何种顺序执行两个任务（自由顺序指令）。两个实验的结果表明，与顺序指令相比，自由顺序下任务顺序控制成本降低，而顺序切换成本不受我们的指令操作影响。这种结果模式表明，任务顺序控制成本反映了任务顺序调节的全局过程，例如参与对顺序指令变化敏感的监测过程，而顺序切换成本反映的是无论协调任务顺序的任何努力都会出现的基于记忆的局部机制。
