Wednesday, November 2, 2011

The benefits of multitasking

The discussion around multitasking usually revolves around the question whether multitasking is bad, with the most extreme position that people just cannot multitask. There are, however, several studies that show that multitasking can sometimes improve your performance. In other words, your performance on task A is better when you combine it with a task B than when you do task A alone!

Doodling for concentration
One example is a study that shows that doodling during meetings improves your recall of what has been said during the meeting. Apparently, it is easier to keep concentrated on boring stuff if you do something, well, boring on the side. For this reason I tell my students that making notes during class is a good idea, even if they never look at those notes again (and I pray that my lectures are not as boring as the doodle meetings). However, in such practical studies it is hard to investigate in detail what is going on.

Attentional Blink
To drill down to the details we did a more controlled laboratory experiment that shows the benefits of multitasking in some situations. The experimental paradigm is called Attentional Blink. In these experiments, subjects see a rapid stream of character, most of which are digits, but up to two characters are letters. Subjects are asked to identify and report the letters, and ignore the digits. You can try out the task yourself here.

In a normal attentional blink trial there are two letters in the stream. Due to the speed of presentation, accuracy is never at 100%, but often around 90%. However, the interesting result in an Attentional Blink experiment is that if the two letters are between 200 and 500 ms apart, the second letter often missed much more often. So while correctness on the first letter may be 90%, it is typically only 50% for the second. Interestingly enough, if either the letters are much closer (say, 100 ms), or much further apart, the second letter is reported correctly as often as the first letter (again, around 90%).

The Attentional Blink effect is interesting itself, and many researchers have been thinking about explanations and models. Additional experimentation showed that in some cases people may improve their performance on the task if you tell them not to try to hard, if they hear music in the background, if there is a starfield in the background, etc. So why is that?

To get a better grasp on this issue, some colleagues and I did a new experiment in which we gave people a second task next to just watching for letters. So we added another task to a task that was in itself already quite hard! The additional task was to track a gray dot that circled around the characters that were presented in the center of the screen. In some trials this gray dot momentarily turned red, and subjects were asked to report this in addition to the letters they saw.
And indeed, the results show that people show less "blink" if they are given the extra task.

Why is multitasking sometimes better?
The advantage of a laboratory task is that we can study what happens in detail. In order to increase our understanding, we built a computer model that mimics human behavior on the task. This model could explain why the Blink happens in the first place: once you have seen the first letter, you try to consolidate this in your memory, and you temporarily block additional letters from cluttering your memory process. In other words: you are too focused on the first letter and therefore miss the second.
If we now add a secondary task, we are slightly disrupting this focus. As a consequence, you will not try to remember the first letter too hard, and therefore also process and remember the second.

Back to the real world
Are you still with me reader? The bottom line is that sometimes we do better on tasks if we are a little distracted by a secondary task. Sometimes our automated processes do a better job than when we focus too much. This can be an issue in sport, for example. If an athlete doesn't trust his or her training, then too much thinking can ruin the effort. Another example: I have a hard time swallowing pills. My trick is to distract myself a bit while trying to swallow, for example by reading the package. I before I know it the pills are gone!


  1. Interesting to read. However, I also came across views against Multitasking, specially in context of learning performance and efficiency. Here is a Dutch article "Het Misverstand Multitasking"

  2. Danzinde,
    The article you refer to takes a black-and-white perspective that I do not think is very scientific. In previous posts I have given examples of multitasking gone wrong, but I resist the idea that multitasking is bad altogether. Otherwise, the article gives two suggestions that they provide as explanations for why we can't multitask. The first points at evolution, which I think only makes sense if you believe our ancestors are strict monotaskers (which I don't, predators would have made minced meat out of us), and the second (although based on an ancient memory model from the sixites) makes some sense, but only when you do multiple tasks that require working memory.