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.

The research on compulsory multi-tasking is at first sight discouraging. Multi-tasking has a bad name. The problem 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.

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.

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.

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 memorize 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 pedaled 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.

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.

Source: www.bbc.com