“Some scientists used to side with my initial gut instinct—they believed it was possible for people to do several complex tasks at once. So they started to get people into labs, and they told them to do lots of things at the same time, and they monitored how well it went. What the scientists discovered is that, in fact, when people think they’re doing several things at once, they’re actually—as Earl explained—“juggling. They’re switching back and forth. They don’t notice the switching because their brain sort of papers it over, to give a seamless experience of consciousness, but what they’re actually doing is switching and reconfiguring their brain moment to moment, task to task—[and] that comes with a cost.” There are three ways, he explained, in which this constant switching degrades your ability to focus. The first is called the “switch cost effect.” There is broad scientific evidence for this. Imagine you are doing your tax return and you receive a text, and you look at it—it’s only a glance, taking five seconds—and then you go back to your tax return. In that moment, “your brain has to reconfigure, when it goes from one task to another,” he said. You have to remember what you were doing before, and you have to remember what you thought about it, “and that takes a little bit of time.” When this happens, the evidence shows that “your performance drops. You’re slower. All as a result of the switching.”
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Johann Hari,
Stolen Focus: Why You Can't Pay Attention—and How to Think Deeply Again