When I state that multitasking is a myth, I am not talking about chatting to a friend on the phone whilst you stir a pot with one hand and close a cupboard door with your foot. I mean mental multitasking: we cannot pay proper attention to more than one thing at a time. The brain can only process one stream of information at a time. What we tend to do when we think we are multitasking (watching the football whilst reading a book, perhaps), is flick between the two. And each time we switch our focus from one thing to the other we have an “attentional blink”, which is a brief period when we are focused on nothing at all. If we try to multi-task a lot these attentional blinks can add up to quite a large block of wasted time.
You may protest that you are very good at multitasking, but just because you think you are does not make it so. Trying to focus on two separate things is asking one piece of apparatus (the “paying attention” part of the brain) to do two things at once. It is akin to trying to whistle and talk at the same time with just the one mouth.
I’m afraid the news gets worse. A study at Stanford University in 2009, conducted by Clifford Ness, split the participants into those who did regular “media multitasking” (watching TV whilst checking emails and Facebook, and so on) and those who didn’t. They were given a series of tasks and the regular multitaskers consistently made more mistakes. It appeared that they could not stop themselves from trying to monitor irrelevant information in their field of view; they could not focus properly on the task in hand.