We all know the feeling. You’re in a noisy office trying to concentrate. Your computer screen shows you have eight different websites open, along with two email accounts, three documents, a spreadsheet, two pdfs and at least one social networking site. You seem to be working on at least five different things and just as you get into one of them, you get an email or message about another and you move onto that instead. You have been at your computer for hours, but it doesn’t feel as though you’re getting anything finished.
And it’s not just at work where the trend for multi-tasking is increasing. In 2014 it was found that 99% of adults use two forms of media simultaneously at some point every week. On average people do this for two hours and three minutes each day. The most popular combination is watching TV at the same time as chatting on the phone.
We could decide not to check our email so frequently or to turn off alerts, but in general we tend not to. Doing two things at once makes us feel as though we’ve somehow saving time, yet there’s still a nagging feeling that finishing one job before starting another might be more efficient.
In psychology the monochronic assumption is the idea that it’s always better to complete one task before you start on the next. In research conducted over several decades, Allen Bluedorn has found that, unsurprisingly, it’s a matter of personal preference. Some people favour monochronicity and feel happier completing one task before they start the next. Others are polychronic and perform better when they are doing lots of things at once, and can excel in jobs which require them to do just that.
Running a busy cafe would be a good example – though this doesn’t mean they necessarily get the jobs done faster. In a cafe there’s no option but to jump from task to task.
The research on compulsory multi-tasking is at first sight discouraging. Multi-tasking has a bad name. Some studies give people two tasks to complete simultaneously. In others multi-tasking means switching backwards and forwards between different tasks until they’re done. So you’re not actually doing them at the same time, but within the same block of time, something that often happens at work.
Sometimes when you concentrate on more than one task at a time there simply isn’t enough cognitive resource to go round
The problem here is something known as attention residue. Experiments have demonstrated that when you switch your attention from one task to another, a bit of your mind is still focused on the previous task. Each time you switch back again you have to remind yourself about what it was you were doing, while dealing simultaneously with the slight distraction from the other task. This can increase your cognitive load.
Sometimes when you concentrate on more than one task at a time there simply isn’t enough cognitive resource to go round. You need to employ attention, working memory and executive function, and the harder the tasks are, the more likely you are to exceed your limit. Then your performance will suffer.
Focusing the mind
Many studies over the years have found that in general people are slower and less accurate when they do two tasks at once. This might suggest that the answer is to complete every task one at a time, but this isn’t always the case. In Sophie Leroy’s experiments on attention residue, this hangover from the previous task disappeared if it had been done under time-pressure.
When people were given a tough deadline, they are forced to narrow their options and to make decisions which are cognitively less complex. This in turn decreases the hangover from that first task, allowing them to put it behind them and get on with the next job. So an approaching deadline not only concentrates the mind, but allows it to clear more easily after it’s passed, leaving us to worry about the next deadline instead.
Multi-tasking is hardest when the tasks are similar to each other, but a bit easier if they are different. So while chatting on the phone and writing an email is difficult, because they involve similar thinking processes in order to generate meaningful sentences, talking while playing the piano isn’t as hard.
If the tasks are different enough then multi-tasking can even improve your performance. A study conducted in 2015 at the University of Florida surprised even its authors. People were asked to sit on exercise bikes and to cycle for two minutes at a speed they found comfortable. Later they cycled again, this time with a screen in front of them which presented them with 12 different types of cognitive tests, some of them quite hard.
If you are a supertasker then you don’t have the same problems the rest of us do
In the easy tests they had to say the word “go” whenever they saw a blue star on the screen; in the harder tasks they had to memorise long lists of numbers and then recite them in reverse order. They completed similar cognitive tests while sitting on a chair in a room and the researchers compared the results.
When people were sitting on an exercise bike they pedalled 25% faster when given mental problems to solve simultaneously, without doing any worse on the problems. This is a case where distraction seems to be useful. The authors speculate that anticipation of the tasks might have increased arousal in the brain, which also made the people more efficient at cycling.
And if you are a supertasker then you don’t have the same problems the rest of us do. Just over 2% of people are brilliant at multi-tasking and suffer no drop in performance. This special group was discovered quite by accident by psychologists at the University of Utah. David Strayer and Jason Watson were investigating why talking on a mobile phone in a car is so much more dangerous than chatting to a passenger who’s in the car with you (the reason is that the passengers naturally cease the conversation whenever things are tricky).
They spotted what they thought must be a mistake in their data – one person who was just as good at driving, whatever the distractions. They rechecked the data and then realised that this individual wasn’t alone. Two people in every hundred are supertaskers, able to divide their concentration effortlessly without their performance suffering.
The intriguing thing about multi-tasking is that although it can increase your cognitive load, many of us still can’t resist working in this way
The problem is that most of us aren’t very good at knowing whether or not we fit into this group. The same psychologists found that the better people believed they were at multi-tasking, the worse they performed on a test which required them to memorise a list of words while also doing maths problem.
But even if you’re not a supertasker, multi-tasking by surfing the web at the same time as answering emails, playing computer games, or listening to music could bring another benefit. Kelvin Lui and Alan Wong from the Chinese University of Hong Kong gave participants a computer task which involved searching for visual information while also responding to certain sounds which could help them with the search. They found people who regularly used three or more different media at a time were better at integrating the information that came in through their ears and their eyes. Since real life involves a lot of integration of different senses this could be a good skill to have.
There are other studies which show that people who use lots of different media at once might have worse working memories, but with these and the Hong Kong study there is always the same problem. Which came first? The skills needed to integrate information and the worse working memory, or the multi-tasking? It’s impossible to randomise someone to many years spent using certain kinds of media. So they’re always self-selecting.
The intriguing thing about multi-tasking is that although it can increase your cognitive load many of us still can’t resist working in this way. When I began writing this article this morning I decided to count how often I chose to check my email or look at some irrelevant site. When I got to 20 I stopped counting. So why do we like it? It seems even if it’s not the most efficient way to work, it feels less of an effort. It certainly can keep us entertained while we work if we do things other than concentrate on the task in hand.
So multi-tasking may have its downsides, but it isn’t always bad. There are certain circumstances under which we are better at multi-tasking – when we feel relaxed and when we’ve been doing a mentally creative exercise which encourages us to think broadly. (In this study it involved thinking of as many uses as possible for a paper clip, a newspaper, some wool and some upholstery foam.) After this kind of activity people became better at multi-tasking. When the experimenters deliberately made them feel stressed, they were worse at it.
One final word on this topic – with all today’s talk of work-life balance and 24 hour schedules, it is worth remembering that the multi-tasking and the pressures of time are not confined to modern life. In 1887, Nietzsche himself described a feeling that seems familiar now: “One thinks with a watch in one's hand even as one eats one's midday meal while reading the latest news of the stock market.”
Join 500,000+ Future fans by liking us on Facebook, or follow us on Twitter, Google+, LinkedIn and Instagram.
If you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.