Multitasking prevents the brain from reorienting its focus:
‘Multitasking isn’t helping you do anything faster, and constant exposure to multiple electronic media makes people really bad at—multitasking. “When you’re pushing yourself to perform two or more tasks, especially complicated tasks, it’s not beneficial,” a researcher tells the Boston Globe. “It’s extremely inefficient.” That’s because no matter how small the task, the brain must reorient its focus.
‘“If you can’t do it in your sleep, it is taking up cognitive energy,” another researcher says, and all the attention shifts during a day of texting and talking and writing can add up to real time. Even extensive practice with multiple media streams doesn’t make you any better at multitasking. In fact, a study shows, it makes you worse: Subjects who habitually juggle electronic tasks are more distracted than their peers. “They couldn’t help thinking about the tasks they weren’t doing,” a researcher explains.’ -Boston Globe