Multi-tasking, task-switching, and humans -- or why I didn't finish writing this post three hours ago

ResearchBlogging.orgDo you multitask? I'm not talking about literally doing two things at once, like emailing while talking on the phone, or playing the trombone while washing the dishes. I'm talking about the more common phenomenon of starting one project before you're finished with another. For example, after I read the journal article I'll be discussing in this post, I caught up on some email correspondence, ordered a new phone for my office, and ate lunch. Now I'm finally getting around to actually writing the post itself. Why didn't I just read the article and then write my post while it was fresh in my mind? Wouldn't that have been more efficient?

There's actually been much more research about the first kind of multitasking -- truly doing two things at once -- than the second type, which might be better characterized as "task switching." But the second type is no less important. Why is it that people seem to switch frequently between tasks, instead of steadfastly working on one task until it is complete?

One bit of evidence has actually come from the study of animal behavior. Suppose a bear is foraging for blueberries. Would it be more efficient for her to eat all the berries from each bush until it's picked clean? Or would it be better to move on to a new bush when berries get harder to find on a given bush? Doesn't it all depend on how plentiful the next bush is? If the next bush is actually sparser than the current bush, then it wouldn't make sense to switch. How does the bear know when to move on?

In 1984, R. F. Green came up with a rule to describe an animal's foraging behavior, using the analogy of a wind-up toy. When the bear encounters a new bush, she makes an estimate of its potential yield, equivalent to winding up the toy the first time. Then as she forages, the toy gradually winds down, but each new berry counteracts that by adding a tiny twist of energy to the toy. If the toy runs completely down before a new berry is found, then she moves on to a new bush. Otherwise, she sticks with the current bush.

Does this rule apply to human task-switching behavior as well? Stephen Payne, Geoffrey Duggan, and Hansjörg Neth developed a simple task to find out. They gave 72 students a 10-minute task: find as many words as possible from each of two separate sets of seven letters. One of the sets was "easy" (the letters LNAOIET), which they had found could create 53 Scrabble words recognizable by a typical college student. The other "hard" set (ESIFLCE) could only create 23 words.

The students were divided into three groups. The first group was required to spend exactly 5 minutes on each task, one after the other. The second group could freely switch between the two tasks whenever they chose, but was again required to spend exactly 5 minutes on each task. The final group could switch between tasks, and was allowed to spend as much time as it wanted on either task (out of the total of 10 minutes). Logically you might expect this last group to spend more time on the easy task, since they could generate more words this way. Here are the results:


As predicted, those in the third group (free switch, flexible time) spent more time on the easy task. But surprisingly this didn't give them an advantage in number of words generated. The group that was forced to spend equal time on each task generated more words. So it appears that while we do try to optimize the time we spend on each task, it doesn't necessarily make us more efficient.

Undaunted, Payne's team proceeded to examine the process people do use to decide when to switch tasks. Does Green's model fit their data? To find out, they examined a key component of the switch from one task to another: How long do people spend trying to find a new word before giving up and switching to the other task? Green's model (which he expressed mathematically in addition to the "wind-up toy" analogy) makes a specific prediction, and the following chart compares Green's prediction with the actual data from this study:


The large area surrounded by the dotted line shows what Green's model predicts, and the smaller elliptical area shows Payne et al.'s data. The two ranges are significantly different from each other -- Green's model doesn't predict what people actually do.

So Payne's team considered an additional factor. They reasoned that people often switch between tasks when they finish an individual subtask (just as I took a break from working on CogDaily when I finished reading this journal article). What constitutes a subtask in this study? When a new word is created. The researchers developed a new model incorporating this element and found that it matched their data! They argue that humans use two independent bases to decide when to switch between tasks -- both Green's "giving up time" and the completion of a subtask.

In another experiment, the team found similar results for a completely different pair of tasks -- solving easy and hard word-search puzzles.

These very simple models give us some insight into why we switch tasks before we finish them, but of course they're just the beginning of the inquiry of how we get work done. After all, they don't explain why I often procrastinate by surfing the web, or why I sometimes repeatedly check my email and answer even the most trivial messages instead of doing the work I should be doing. That will have to wait for their next study... unless they decide to move on to a different line of research first!

Stephen J. Payne, Geoffrey B. Duggan, Hansjörg Neth (2007). Discretionary task interleaving: Heuristics for time allocation in cognitive foraging. Journal of Experimental Psychology: General, 136 (3), 370-388 DOI: 10.1037/0096-3445.136.3.370

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This is hitting a bit too close to home, as I have been working on a paper for three hours, but spending lots of time checking my email in between. ;P

I view switching to another task as my reward for completing a subtask. It makes my overall task more "manageable", and prevents me from getting too stressed out, IMO.

I would like to see another study where they assign different rewards to each type of task "easy" and "hard"... first that comes to mind is small reward for easy and comparatively big reward for hard. But let's not stop there! how about psychological rewards for one and material awards for the other? how about instant gratification for one, delayed gratification for the other? Ooh and what about individual-based performance rewards for one and team-based performance rewards for another?

By Stephanie (not verified) on 23 Jun 2008 #permalink

I am a serious task-switcher. At any given moment, I am typically switching back and forth between windows on my computer that contain (1) grant appication(s) I am writing/revising, (2) paper manuscript(s) I am writing/revising, (3) paper manuscript(s) I am peer reviewing, (4) grant application(s) I am peer reviewing, (5) e-mail, (6) blog reader, (7) several different on-line discussion forums I participate in, (8) blog writing.

I haven't really timed my switching, but I would say that I spend the longest intervals of time on the grant and manuscript reviewing and blog writing (I'm guessing ~7 minutes on average before switching to something else), next longest on the grant and manuscript writing (~5 minutes), and shortest on the e-mail, blog reading, and forums. The majority of my blog posts get written completely in one 7 minute interval.

I haven't noticed that it slows me down to switch back and forth like this--though I may be kidding myself. It doesn't seem to take me more than a second or two to get myself exactly where I was on any given task before I switched away from it.

That's basically the ONLY way I operate----I was diagnosed with possible adult ADD, but I prefer to think of it as being extremely right-brained.

At one time I fell into a mental state such that whatever I was doing, I felt like I should be doing something else. This got so bad that I mostly dithered, could accomplish very little, and was quite unhappy and frustrated. One day, my youngest son asked me to take him fishing for the first time. Sitting on the river bank, a light bulb went off over my head. I suddenly understood that when one is fishing one is NOT supposed to be doing anything else. This great revelation was the turning point. I started using a timer and disciplining myself to work on a single task until the timer went off. Soon I was my former happy, productive self. Focus and drive!

By Jim Thomerson (not verified) on 23 Jun 2008 #permalink

Interesting! I would like to see how this all relates to people with ADD. My husband and I both have ADD (never a dull moment here), and in our experiences, performing multiple tasks at the same time is very easy. Attempting to switch between multiple tasks, however, is a recipe for disaster!

I think that by researching this further, we can find ways to help people strategize living with ADD, without having to resort to medication (not that I'm anti-medication, just pro-research).

Putting myself in this experiment, I think I would make a task switch from "hard" to "easy" which may be interpreted as laziness. But, actually, maybe its a goal-oriented pride that made the students switch to the easier list. They wanted to be able to find as many words as possible and learned that could be done with the easier set of letters. So, instead of lack of focus, it was actually the search for higher productivity? OK, so I'm in denial about my wandering brain, but I can still rationalize well!

I don't do any of this stuff. I do, however, play the trombone while I'm washing the dishes. While I'm emailing my mother. In Dutch. With my foot.

For tasks that don't require significant context, I'll switch away merrily. However, I often have tasks that require a great deal of context (say, debugging a complex piece of code). In that case, I will spend hours happily immersed in that single task, and will get seriously annoyed if something interrupts me and causes me to lose my mental state.

Perhaps it's just the programmer in me (to a person with a hammer, everything looks like a nail, and to a programmer, everything looks like a processor :-). But to me, this looks like a "cost of context switch" algorithm.

Good study and interesting, but I think you have missed a factor which must be included in any model of actual human behavior: fatigue and/or boredom.

In any task I am engaged in, unless the task is very interesting, I rapidly tire of the task, do something else, then return to the task until the task is completed.

Particularly if the task requires insight (which most do), the break(s) also allows time for creativity to surface.

By Jerry Park (not verified) on 24 Jun 2008 #permalink

This is very interesting and pertinent for me! Avoiding tasks and/or becoming intensely engrossed in 'optional' tasks at the expense of 'necessary' tasks, is a major stumbling block in my life - and as I am married, impinges on my longsuffering wife's life too.

I exhibit Asperger Syndrome traits (self-diagnosed, peer-recognised, clinically-indicated) but not definitively diagnosed as yet.
While a diagnosis (which I am seeking) may be helpful, I am more interested in finding apt ways to manage my attention and focus, to enhance productivity (and domestic bliss).

These have been lifelong difficulties. However there is the advantage at times of being able to intensively pursue a single project and be 'in the zone' of an unusually high degree of awareness, insight and creativity within that focus. This may be common to many - artists, musicians, academics, sculptors etc.

I am sure that (as people generally fall along a spectrum) there may be many (whether 'Aspie' or not) who'd like to benefit from such research as you describe - both overcoming the difficulties, and harnessing the benefits, of attention-management.


By Graham King (not verified) on 24 Jun 2008 #permalink

There is a hidden implication here that when a task is switched, all available mental resources are then devoted to the new task. This may be true for some, but not everybody (YMMV). I find that my subconscious keeps gnawing at suspended tasks and I suspect that task switching improves my overall performance by using both foreground and background processing. Of course, this may only be self-delusion.... but it may be like a placebo: it works as long as I believe that it does.

By WuffenCuccoo (not verified) on 24 Jun 2008 #permalink

what would personally interest me is how prefrontal dopamine levels change while switching tasks.

anyway, a very interesting study!

very useful article, I currently working on a project, and just keep wondering on the internet until I found this article and thinking, "wait, is he talking to me?"

thanks for the advice

I find that my subconscious keeps gnawing at suspended tasks and I suspect that task switching improves my overall performance by using both foreground and background processing.

This is my experience as well.

Great post, ditto on the comments. Background processing is key to my performance. On multiple occasions, I recall struggling to solve an assigned problem in college, giving up, then (a) playing the piano or (b) crawling into bed. Voila! The solution I'd been seeking would suddenly come to me, within 10 minutes of giving up (that is, giving up the foreground processing). I call it creativity, as I'm sure the problem moved to another part of the brain at that point. Being one of those ADHD types, I allow myself to switch from task to task until they all get done. May not appear efficient, but it works for me.

--Lisa S.

Comments #12, #15, and #16 raise a very important point. Studies of creativity have repeatedly shown that major creative leaps (the big brainstorms) are often done in a three-step process:

1. Internalize the problem. Agonize over it, Sweat. Work. Struggle.
2. Give up. Go do something else.
3. Poof! Solution appears later.

The implication is that you need to push the problem down into lower levels of processing and let it simmer. And task switching does exactly this. I have developed work habits that emphasize task switching as a regenerative process. I'll work on computer programming for a while, until I sense that I'm hitting some sort of roadblock. Then I switch to writing or some other computer task. Or perhaps I'll switch to something social -- talking to colleagues, perhaps. And there's always a point at which there has been too much mental activity and I need to go outside and do mindless physical labor. That clears my mind and sets me up to resume the hard mental labor.

By Chris Crawford (not verified) on 26 Jun 2008 #permalink

The implication is that you need to push the problem down into lower levels of processing and let it simmer. And task switching does exactly this. I have developed work habits that emphasize task switching as a regenerative process.

With respect to my former comment: Is there possibly a connection between this (alleged) effect and the Zeigarnik effect?

By WuffenCuckoo (not verified) on 30 Jun 2008 #permalink

Doing two or more things at once, like emailing while working on a project is not so good . IMHO Task-switching or better contest switching every 5 minutes causes stress . Can be done , but with a cost. Some info googling "multitasking and stress".

Holly macaroni, this is me!!!!. Right now I'm trying to finish my study yet i spent and enjoys spending time with other staff in few minutes. I can't focus on the things i really need to do. I easily get distracted. Right now then i saw my Google reader and found this message and without realizing I'm making a comment about this article right now. Also the studies that they have done was accurate. My girlfriend and I play Scrabble words and she'd always win; however, I considerably better than her in school academic staff.