## 4 Experiment
### Independent Variables: Types of Tasks and Interruption Coordination Modes  
Because this study was focused on evaluating the interruption cost, selected tasks needed to be described more broadly as the individual's general activity, and needed to include distinctive cognitive processes to complete the task. A cognitive task requires a high level of cognitive demand and is sensitive to individual differences and errors. In this study, arithmetic word problems using only basic arithmetic operations were chosen. Reading comprehension skills and arithmetic operation capability were the main cognitive resources for completing these tasks. On the other hand, sentence copying tasks in which given sentences were typed with a computer keyboard were selected as the skill task. The skill task highly depends on motor skill ability and visual-spatial processing. The main performance criterion was how fast participants completed typing without typographical errors. In addition, the number of words in both tasks was controlled similarly to minimize the effects of individual differences. Table 2 shows some examples of cognitive and skill tasks used in this study.  
As another independent variable, three interruption coordination modes based on [PERSON]'s four modes of interruption coordination [32] were designed and implemented. Each mode indicates different interfaces to interact with interruptions. In the immediate mode, an interrupting task appeared while a primary task was performed without any notice. An interruption was immediately delivered regardless of the status and progress of primary tasks. Participants could not control the occurrence of interruptions. In the negotiated mode, participants were notified that the interruption  
\begin{table}
\begin{tabular}{l} \hline \hline
**Cognitive Task: Mathematical Question Solving 1** \\ \hline A certain property doubled in value from 1950 to 1960 and tripled in value from 1960 to 1980. The value of the property in 1980 was how many times the value in 1950? \\ a. 3 & b. 5 \\ \hline
**Physical Task: Sentence Copying 2** \\ \hline Type the following sentences in the given space. \\ The specific and detailed structure is difficult to be obtained. Healthcare Information and Management System Society introduced a view about healthcare systems including the Electronic Health Record and the Electronic Medical Record. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Sample questions for cognitive and skill tasks.  
would occur, and they could control the onset of an interruption by clicking a button on the screen. In the scheduled mode, participants acknowledged the onset of an interrupting task after a primary task was given. Though participants could expect when an interruption occurred, they could not manipulate the given schedule. In the experiment, once the primary task was given, the peripheral task popped up after 15 s. A countdown timer informed the participant of the remaining time before the task had to be completed.  
The other mode, \"mediated mode\", was not included in this study. In a mediated mode, the agent crucially decides when and how the interruption is initiated, and this controversial process requires interruptibility prediction, intelligent interfaces, precise cognitive workload measurement, human factors techniques, and a cognitive model to supervise the mediator [32]. Thus, the impact of the mediated mode on an actual user's cognitive workload would be minimal, and this mode has a quite different mechanism for the interruption interaction from that of other modes.