We compared task performance time and psychological reactions for uninterrupted, single interrupted, and multiple interrupted conditions. For 110 undergraduates, those who were uninterrupted while completing a jigsaw puzzle were 26% faster than the single interruption, and 30% faster than the multiple interruption conditions. Single and multiple interruption conditions were not significantly different. Participants in the multiple interruption condition felt more stress than those in the uninterrupted condition, although stress levels were low in both conditions. Perceptions of time pressure and flow were not different across conditions. Performance on the interrupting task (a word search puzzle) was not significantly different across conditions. An interruption or multiple interruptions significantly and substantially slowed performance although participants were not psychologically bothered by being interrupted.
Conard, Maureen A. and Marsh, Robert, "Single And Multiple Interruptions Increase Task Performance Time, But Don't Affect Stress, Pressure or Flow" (2010). WCBT Working Papers. 1.