As systems grow in complexity, there are more tasks that people want to complete simultaneously. Prior research has shown that receiving interruptions hurts people's performance. Our research intends to better understand the performance implications of users multitasking during simple and complex tasks by examining task difficulty both objectively and subjectively. We created a web-based word search puzzle as the primary task with an objectively easy and hard version. 726 were randomized into

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... e of four conditions. In the first two conditions, participants received the objectively easy or hard version of the primary task and did not receive any interruptions. In the latter two conditions participants received the easy and hard versions with interruptions. Subjective difficulty was measured based on the participants' opinions of the primary task. While we did not find any significant differences in conditions with the objective or subjective divisions, however, when participants perceived the interrupting task as difficult receiving interruptions during both the easy and hard conditions helped participants perform better. This was only true for the subjective breakdown. These findings suggest that the difficulty level of the interrupting task may impact users' performance outcome when receiving interruptions. We also found that while there was no significant correlation between participants' propensity to multitask and performance in the interrupting conditions, when examining those who did not receive interruptions, participants' performance significantly positively correlated with their propensity to multitask. This implies that multitasking users perform better than non-multitasking users when mono-tasking.