It's called "contextual jitter" -- in the time it takes to silence your cell phone, you've already lost track of what you were doing.
PROBLEM: Being interrupted is annoying, and, for those of us always with our phones on us, basically a constant. But how detrimental is it to us actually getting things done?
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METHODOLOGY: Michigan State University researchers assigned 300 volunteers a rather complicated computer task -- basically, they had to follow a number of steps, and doing so correctly depended on them remembering where they were in the sequence. Kind of like an artificially imposed train of thought, which would then be broken by the researchers asking them to complete a quick side-task.
RESULTS: All of the participants made minor errors; no one's perfect. But when their attention was shifted from the task at hand for a mere 2.8 seconds, they became twice as likely to mess up the sequence. The error rate tripled when the interruptions averaged 4.4 seconds.
Worryingly, there wasn't any lag time between being interrupted and getting back to work, meaning the participants didn't seem to realize that they had been thrown off.
CONCLUSION: "When someone is momentarily interrupted or distracted and then returns to their task, they may do so without obvious hesitation, but with an increased chance of resuming at a different point in their train of thought than they might have otherwise," write the authors. They even have a name for it: "contextual jitter."
IMPLICATIONS: Don't panic. But they do make it relevant in a public health context; the lead researcher Erik Altmann said, "What this means is that our health and safety is, on some level, contingent on whether the people looking after it have been interrupted." So, cell phone on silent when you need to work. Especially those of you with life-or-death, sequence-based jobs to do, please.
The full study, "Momentary Interruptions Can Derail the Train of Thought," is published in the Journal of Experimental Psychology: General.