| Summary: | 碩士 === 國立清華大學 === 資訊系統與應用研究所 === 94 === 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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