作業轉換研究的二十年回顧：還有什麼議題可繼續追問？

Two Decades of Research on Task Switching: What More Can We Ask?

高等認知控制的重要面向之一是能夠因應環境而有效率的在不同作業之間做轉換。例如，一位雙語者必須能夠依據她／他所談話的對象來決定使用哪一種語言做溝通，並且要能夠隨時在必要時去轉換使用不同的語言。既然在任何一個情境脈絡下都存在許多的不同作業可以執行，那麼究竟我們是如何去控制使用這些與時俱變的不同作業已成為一個重要的研究課題。在過去的二十年，許多為理解動力性認知控制的研究者已普遍使用「作業轉換」的程序：要求實驗參與者要對兩種不同的作業規則做嘗試次之間的快速轉換。透過這個作業程序，研究者發現實驗參與者轉換作業時所須花費的時間要比重複作業來得長。本篇回顧性文章將總覽過去二十年來使用各種不同類型的作業轉換派典之相關研究，包括行為的以及神經影像為取向的研究。本文將著重於作業轉換的準備控制機制（轉換特定性及／或一般性）及其相關理論。同時文中將評述作業轉換的各種干擾現象，包括作業轉換的反應重覆虧損、作業前向干擾、後向抑制、作業規則相容性、競爭規則抑制等等。最後，文中將展望作業轉換之研究未來十年的可行性研究議題。

A key aspect of higher cognitive control is the ability to switch efficiently between alternative tasks in a manner that is appropriate to the situation. For instance, a bilingual speaker needs to control which language she/he uses depending upon who is being spoken to and to switch between languages when necessary. Since in any given context there is a range of tasks that could be performed, the question arises of how we control our use of different tasks over time. Much of the research into dynamic cognitive control for the past two decades has employed the “task switching” procedure which requires participants to respond to stimuli according to one of two alternative task-rules and switch the appropriate task-rule from trial to trial. Researchers have consistently found in such procedure that participants require more time in switching between two tasks than in merely repeating one task. In this article, I will review studies that have been conducted for the past two decades with various forms of task-switching paradigms and by use of behavioral and neuroimaging approaches. The review focuses on preparatory control mechanisms (switch-specific and/or generic) and theoretical accounts in task switching. The review also focuses on various interference phenomena in task switching, including switch response-repetition cost, proactive interference of tasks, backward inhibition, task rule congruency effect, and competitor rule suppression. Finally, I will provide perspectives on future research for the next decade.