提示系統（Notification System）是一種於使用者工作進行中給予額外訊息的應用軟體。使用者當下正在進行的工作為主要任務，提示系統所提供的資訊則為次要任務。由於以往針對任務複雜度所進行的相關研究，僅單方面探討主要或次要任務的複雜度，主、次要任務複雜度對於績效影響的說法不一致，以至於研究結果相互衝突或是用來解釋的理論不夠完善。因此，本研究同時操弄主要與次要任務複雜度，來探究提示系統中任務複雜度對於使用者工作績效、恢復間歇（Resumption lag）與中斷效果的關係。恢復間歇係指使用者結束次要任務後用來準備回復主要任務情境的一段時間。研究中透過實驗來探討不同程度的任務複雜度如何因人類訊息處理能力的限制，而對使用者的績效與主觀感受造成影響，藉此提出任務複雜度的設計方法，以縮短恢復間歇時間並減輕中斷的負面影響。
本研究採用2 x 2的實驗設計。自變項為主要任務與次要任務的複雜度（簡單或複雜），應變項為使用者工作績效（包括主要及次要任務的正確率與處理時間）、恢復間歇、焦慮程度與主觀任務複雜度。本研究主要任務為產品搜尋，依照產品內容以及題目要求而區分為簡單與複雜；次要任務則為數學運算題，依據需解碼與否以及需計算的項目亦區分為簡單與複雜。研究結果顯示主要或次要任務正確率與處理時間直接受到該任務本身複雜度的影響。四組整體績效為主、次要任務皆為簡單組優於主要複雜與次要簡單組優於主要簡單與次要複雜組優於主、次要任務皆為複雜組。恢復間歇受到次要任務複雜度的影響甚鉅，次要任務越複雜則回復到主要任務的困難度亦會增加。主要任務被打斷會對使用者產生壓力及分散對主要任務的注意力。本研究結果建議於提示系統環境中，當中斷無可避免時設計者必須嚴格控制次要任務的複雜度，使執行任務的時間不超過30秒（人類訊息處理之能力範圍），進而將次要任務所造成的打斷效果減到最低。

A notification system is an application software which delivers extra messages to users while they are working. To the user, the primary task is the ongoing task; the messages delivered by the notification system are secondary one. Because the past studies only focused on the complexity of a single task (primary or secondary), their results often conflicted with each other, and their theories don’t have enough explanatory power. Therefore, this study focuses on both the complexity of the primary and that of the secondary task, and discusses the relationships among task complexity in the notification system, users’ performance, resumption lag, and the effects of interruptions. Resumption lag is the time between the termination of the secondary task and the beginning of the primary task. This study conducted an experiment to show how different levels of task complexity affect users’ performance and their subjective feelings due to human limitation on information processing. We provide design methods for task complexity to shorten the resumption lag and mitigate the negative effects of interruptions.
This study was a 2 x 2 between-subjects design. The independent variables were the complexity of the primary and that of the secondary task at two levels (simple and complex). The dependent variables were users’ performance (including the accuracy and the completion time of the task), resumption lag, the state of anxiety, and subjective task complexity. The primary task was product searching at two levels, simple and complex, according to product information and the specified constraints. The secondary task was arithmetic problem-solving, which also has two levels, simple and complex, depending on whether the subject is required to decode the digits and the numbers of digits to be calculated. The results show that the accuracy and completion time of a task either primary or secondary, is only influenced by it self. The overall performance of the four groups is that SS group is better than CS group, which in turn is better than SC group, and CC group is the worst. The influence of the secondary task complexity on resumption lag is great. In other words, the more complex the secondary task is, the harder it is for the subject to resume the primary task. Being interrupted while doing the primary task, the users would have pressure and feel difficult to resume concentration on the primary task. The study suggests that while interruptions are unavoidable with the notification system, the designer should control the complexity of the secondary task to the least and restrict the completion time within 30 seconds.

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