Doing more than one task at a time requires us to switch our attention rapidly between the tasks.

This is easier if the tasks don't need much attention.

Although we think we're saving time, time is lost when switching between tasks; these time costs increase for complex or unfamiliar tasks.

Both alcohol and aging affect our ability to switch attention rapidly.

A very common situation today, which is probably responsible for a great deal of modern anxiety about failing memory, is that where we're required to “multitask”, that trendy modern word for trying to do more than one thing at a time. It is a situation for which both the normal consequences of aging and low working memory capacity has serious implications.

There’s an old insult along the lines of “he can’t walk and chew gum”. The insult is a tacit acknowledgment that doing two things at the same time can put a strain on mental resources, and also recognizes (this is the insult part!) that well-practiced activities do not place as much demand on our cognitive resources. We can, indeed, do more than one task at a time, as long as only one of the tasks requires our attention. It is attention that can’t be split.

You may feel that you can, in fact, do two tasks requiring attention simultaneously. For example, talking on a cellphone and driving!

Not true.

What you are in fact doing, is switching your attention rapidly between the two tasks, and you are doing it at some cost.

How big a cost depends on a number of factors. If you are driving a familiar route, with no unexpected events (such as the car in front of you braking hard, or a dog running out on the road), you may not notice the deterioration in your performance. It also helps if the conversation you are having is routine, with little emotional engagement. But if the conversation is stressful, or provokes strong emotion, or requires you to think … well, any of these factors will impact on your ability to drive.

The ability to switch attention between tasks is regulated by a function called prefrontal cortex. This region of the brain appears to be particularly affected by aging, and also by alcohol. Thus, talking on a cellphone while driving drunk is a recipe for disaster! Nor do you have to actually be under the influence to be affected in this way by alcohol; impaired executive control is characteristic of alcoholics.

More commonly, we get older, and as we get older we become less able to switch attention fast.

The ability to switch attention is also related to working memory capacity.

But multitasking is not only a problem for older adults, or those with a low working memory capacity. A study [1] using young adults found that for all types of tasks, time was lost when switching between tasks, and time costs increased with the complexity of the tasks, so it took significantly longer to switch between more complex tasks. Time costs also were greater when subjects switched to tasks that were relatively unfamiliar.

Part of the problem in switching attention is that we have to change “rules”. Rule activation takes significant amounts of time, several tenths of a second — which may not sound much, but can mean the difference between life and death in some situations (such as driving a car), and which even in less dramatic circumstances, adds appreciably to the time it takes to do tasks, if you are switching back and forth repeatedly.

To take an example close to home, people required to write a report while repeatedly checking their email took half again as long to finish the report compared to those who didn't switch between tasks!

In other words, while multitasking may seem more efficient, it may not actually BE more efficient. It may in fact take more time in the end, and the tasks may of course be performed more poorly. And then there is the stress; switching between tasks places demands on your mental resources, and that is stressful. (And not only are we poorer at such task-switching as we age, we also tend to be less able to handle stress).

There is another aspect to multitasking that deserves mention. It has been speculated that rapid switching between tasks may impede long-term memory encoding. I don’t know of any research on this, but it is certainly plausible.

So, what can we do about it?

Well, the main thing is to be aware of the problems. Accept that multitasking is not a particularly desirably situation; that it costs you time and quality of performance; that your ability to multitask will be impeded by fatigue, alcohol, stress, emotion, distraction (e.g., don’t add to your problems by having music on as well); that your ability will also be impaired by age. Understand that multitasking involves switching attention between tasks, not simultaneous performance; and that it will therefore be successful to the extent that the tasks are familiar and well-practised.

This article originally appeared in the February 2005 newsletter.

  1. Rubinstein, J.S., Meyer, D.E. & Evans, J.E. 2001. Executive Control of Cognitive Processes in Task Switching. Journal of Experimental Psychology - Human Perception and Performance, 27 (4), 763-797.

Frequent multitaskers are the worst at it

A survey of college students found that those who scored highest in multitasking ability were also least likely to multitask, while those who scored lowest were most likely to engage in it.

I’ve reported often on the perils of multitasking. Here is yet another one, with an intriguing new finding: it seems that the people who multitask the most are those least capable of doing so!

The study surveyed 310 undergraduate psychology students to find their actual multitasking ability, perceived multitasking ability, cell phone use while driving, use of a wide array of electronic media, and personality traits such as impulsivity and sensation-seeking.

Those who scored in the top quarter on a test of multitasking ability tended not to multitask. Some 70% of participants thought they were above average at multitasking, and perceived multitasking ability (rather than actual) was associated with multitasking. Those with high levels of impulsivity and sensation-seeking were also more likely to multitask (with the exception of using a cellphone while driving, which wasn’t related to impulsivity, though it was related to sensation seeking).

The findings suggest that those who multitask don’t do so because they are good at multitasking, but because they are poor at focusing on one task.

Shaping your cognitive environment for optimal cognition

Urbanization appears to increase working memory capacity, and decrease focus.

This may reflect the increased cognitive demands of the urban environment.

The reduced ability to ignore distraction typically seen in aging may reflect not only physiological changes such as decreases in processing speed, but also the speed and complexity of the modern environment.

To increase working memory capacity, specific training programs may be the wrong approach. Instead, we should incorporate challenging activities into our daily routine.

To improve focus, we should regularly engage in activities that absorb and challenge us.

Humans are the animals that manipulate their cognitive environment.

Even tiny interruptions can double or treble work errors

A new study quantifies the degree to which tasks that involve actions in a precise sequence are vulnerable to interruptions.

In my book on remembering intentions, I spoke of how quickly and easily your thoughts can be derailed, leading to ‘action slips’ and, in the wrong circumstances, catastrophic mistakes. A new study shows how a 3-second interruption while doing a task doubled the rate of sequence errors, while a 4s one tripled it.

The study involved 300 people, who were asked to perform a series of ordered steps on the computer. The steps had to be performed in a specific sequence, mnemonically encapsulated by UNRAVEL, with each letter identifying the step. The task rules for each step differed, requiring the participant to mentally shift gears each time. Moreover, task elements could have multiple elements — for example, the letter U could signal the step, one of two possible responses for that step, or be a stimulus requiring a specific response when the step was N. Each step required the participant to choose between two possible responses based on one stimulus feature — features included whether it was a letter or a digit, whether it was underlined or italic, whether it was red or yellow, whether the character outside the outline box was above or below. There were also more cognitive features, such as whether the letter was near the beginning of the alphabet or not. The identifying mnemonic for the step was linked to the possible responses (e.g., N step – near or far; U step — underline or italic).

At various points, participants were very briefly interrupted. In the first experiment, they were asked to type four characters (letters or digits); in the second experiment, they were asked to type only two (a very brief interruption indeed!).

All of this was designed to set up a situation emulating “train of thought” operations, where correct performance depends on remembering where you are in the sequence, and on producing a situation where performance would have reasonably high proportion of errors — one of the problems with this type of research has been the use of routine tasks that are generally performed with a high degree of accuracy, thus generating only small amounts of error data for analysis.

In both experiments, interruptions significantly increased the rate of sequence errors on the first trial after the interruption (but not on subsequent ones). Nonsequence errors were not affected. In the first experiment (four-character interruption), the sequence error rate on the first trial after the interruption was 5.8%, compared to 1.8% on subsequent trials. In the second experiment (two-character interruption), it was 4.3%.

The four-character interruptions lasted an average of 4.36s, and the two-character interruptions lasted an average of 2.76s.

Whether the characters being typed were letters or digits made no difference, suggesting that the disruptive effects of interruptions are not overly sensitive to what’s being processed during the interruption (although of course these are not wildly different processes!).

The absence of effect on nonsequence errors shows that interruptions aren’t disrupting global attentional resources, but more specifically the placekeeping task.

As I discussed in my book, the step also made a significant difference — for sequence errors, middle steps showed higher error rates than end steps.

All of this confirms and quantifies how little it takes to derail us, and reminds us that, when engaged in tasks involving the precise sequence of sub-tasks (which so many tasks do), we need to be alert to the dangers of interruptions. This is, of course, particularly true for those working in life-critical areas, such as medicine.


[3207] Altmann, E. M., Gregory J., & Hambrick D. Z. (2013).  Momentary Interruptions Can Derail the Train of Thought. Journal of Experimental Psychology: General. No - Pagination Specified.

When multitasking is more of a problem

Multitasking is significantly worse if your tasks use the same modality. Instant messaging while doing another visual-motor task reduces performance more than talking on the phone.

I’ve reported, often, on the evidence that multitasking is a problem, something we’re not really designed to do well (with the exception of a few fortunate individuals), and that the problem is rooted in our extremely limited working memory capacity. I’ve also talked about how ‘working memory’ is a bit of a misnomer, given that we probably have several ‘working memories’, for different modalities.

It follows from that, that tasks that use different working memories should be easier to do at the same time than tasks that use the same working memory. A new study confirms that multitasking is more difficult if you are trying to use the same working memory modules for both tasks.

In the study, 32 students carried out a visual pattern-matching task on a computer while giving directions to another person either via instant messaging (same modalities — vision and motor) or online voice chat (different modality — hearing).

While both simultaneous tasks significantly worsened performance on the pattern-matching task, communicating by IM (same modality) led to a 50% drop in visual pattern-matching performance (from a mean of 11 correct responses to a mean of 5), compared to only a 30% drop in the voice condition (mean of 7).

The underlying reason for the reductions in performance seems to be in the effect on eye movement: the number and duration of eye fixations was reduced in both dual-task conditions, and more so in the IM condition.

Note that this is apparently at odds with general perception. According to one study, IM is perceived to be less disruptive than the phone. Moreover, in the current study, participants felt they performed better in the IM condition (although this palpably wasn’t true). This feeling may reflect the greater sense of personal control in instant messaging compared to chat. It may also reflect an illusion of efficiency generated by using the visual channel — because we are so strongly practiced in using vision, we may find visual tasks more effortless than tasks using other modalities. (I should note that most people, regardless of the secondary task, felt they did better than they had! But those in the IM condition were more deluded than those in the chat condition.)

The finding also explains why texting is particularly dangerous when driving — both rely heavily on the same modalities.

All this is consistent with the idea that there are different working memory resources which can operate in parallel, but share one particular resource which manages the other resources.

The idea of ‘threaded cognition’ — of maintaining several goal threads and strategically allocating resources as needed — opens up the idea that multitasking is not all bad. In recent years, we have focused on multitasking as a problem. This has been a very necessary emphasis, given that its downsides were unappreciated. But although multitasking has its problems, it may be that there are trade-offs that come from the interaction between the tasks being carried out.

In other words, rather than condemning multitasking, we need to learn its parameters. This study offers one approach.

How meditation may improve multitasking and attention

Three recent studies show that meditation training reduces the stress of multitasking and reduces task-switching, that it improves white matter efficiency, and that the improved executive control may be largely to do with better emotional awareness and regulation.

Meditation may improve multitasking

I recently reported that developing skill at video action games doesn’t seem to improve general multitasking ability, but perhaps another approach might be more successful. Meditation has, of course, been garnering growing evidence that it can help improve attentional control. A new study extends that research to multitasking in a realistic work setting.

The study involved three groups of 12-15 female human resource managers, of whom one group received eight weeks of mindfulness-based meditation training, another received eight weeks of body relaxation training, and another initially received no training (control), before receiving the mindfulness training after the eight weeks.

Before and after each eight-week period, the participants were given a stressful test of their multitasking abilities, requiring them to use email, calendars, instant-messaging, telephone and word-processing tools to perform common office tasks (scheduling a meeting; finding a free conference room; writing a draft announcement of the meeting, eating snacks and drinking water, writing a memo proposing a creative agenda item for the meeting). Necessary information came from emails, instant messages, telephone calls, and knocks on the door. The participants had 20 minutes to complete the tasks.

The meditation group reported lower levels of stress during the multitasking test compared to the control and relaxation groups. They also spent more time on tasks and switched tasks less often, while taking no longer to complete the overall job than the others. Both meditation and relaxation groups showed improved memory for the tasks they were performing.

After the control group underwent the meditation training, their results matched those of the meditation group.

The meditation training emphasized:

  • control of attentional focus
  • focusing attention in the present moment or task
  • switching focus
  • breath and body awareness.

The relaxation training emphasized progressive tensing and relaxing of major muscle groups, aided by relaxation imagery.

It's interesting that overall time on task didn't change (the researchers remarked that the meditators didn't take any longer, but of course most of us would be looking for it to become shorter!), but I wouldn't read too much into it. The task was relatively brief. It would be interesting to see the effects over the course of, say, a day. Nor did the study look at how well the tasks were done.

But it is, of course, important that meditation training reduced task-switching and stress. Whether it also has a postitive effect on overall time and quality of work is a question for another day.

IBMT improves white matter efficiency

A recent imaging study has found that four weeks of a form of mindfulness meditation called integrative body–mind training (IBMT) improved white matter efficiency in areas surrounding the anterior cingulate cortex, compared to controls given relaxation training.

The anterior cingulate is part of the brain network related to self-regulation. Deficits in activation in this part of the brain have been associated with attention deficit disorder, dementia, depression, schizophrenia, and other disorders.

Using the data from a 2010 study involving 45 U.S. college students, and another involving 68 Chinese students, researchers found that axon density (one factor in white matter efficiency) had improved after two weeks, but not myelin formation. After a month (about 11 hours of meditation), both had improved. Mood improved by two weeks.

Previous studies involving computer-based training for improving working memory have found changes in myelination, but not axon density.

Meditators’ better cognitive control may be rooted in emotional regulation

Previous work has found that people who engage in meditation show higher levels of executive control on laboratory tasks.

An electrical signal called the Error Related Negativity (ERN) occurs in the brain within 100 ms of an error being committed. When meditators and non-meditators were given the Stroop Test, meditators not only tended to do better on the test, but their ERNs were stronger.

The interesting thing about this is that the best performers were those who scored highest on emotional acceptance. Mindful awareness was less important. It’s suggested that meditators may be able to control their behavior better not because of their sharper focus, but because they are more aware of their emotions and regulate them better.

Something to think about!


Levy, D. M., Wobbrock, J. O., Kaszniak, A. W., & Ostergren, M. (2012). The Effects of Mindfulness Meditation Training on Multitasking in a High-Stress Information Environment, 45–52. Full text available at

[3051] Tang, Y. - Y., Lu Q., Fan M., Yang Y., & Posner M. I. (2012).  Mechanisms of white matter changes induced by meditation. Proceedings of the National Academy of Sciences. 109(26), 10570 - 10574.

[3052] Teper, R., & Inzlicht M. (2012).  Meditation, mindfulness and executive control: the importance of emotional acceptance and brain-based performance monitoring. Social Cognitive and Affective Neuroscience.

Video gamers don’t become expert multitaskers

A comparison of skilled action gamers and non-gamers reveals that all that multitasking practice doesn’t make you any better at multitasking in general.

The research is pretty clear by this point: humans are not (with a few rare exceptions) designed to multitask. However, it has been suggested that the modern generation, with all the multitasking they do, may have been ‘re-wired’ to be more capable of this. A new study throws cold water on this idea.

The study involved 60 undergraduate students, of whom 34 were skilled action video game players (all male) and 26 did not play such games (19 men and 7 women). The students were given three visual tasks, each of which they did on its own and then again while answering Trivial Pursuit questions over a speakerphone (designed to mimic talking on a cellphone).

The tasks included a video driving game (“TrackMania”), a multiple-object tracking test (similar to a video version of a shell game), and a visual search task (hidden pictures puzzles from Highlights magazine).

While the gamers were (unsurprisingly) significantly better at the video driving game, the non-gamers were just as good as them at the other two tasks. In the dual-tasking scenarios, performance declined on all the tasks, with the driving task most affected. While the gamers were affected less by multitasking during the driving task compared to the non-gamers, there was no difference in the amount of decline between gamers and non-gamers on the other two tasks.

Clearly, the smaller effect of dual-tasking on the driving game for gamers is a product of their greater expertise at the driving game, rather than their ability to multitask better. It is well established that the more skilled you are at a task, the more automatic it becomes, and thus the less working memory capacity it will need. Working memory capacity / attention is the bottleneck that prevents us from being true multitaskers.

In other words, the oft-repeated (and somewhat depressing) conclusion remains: you can’t learn to multitask in general, you can only improve specific skills, enabling you to multitask reasonably well while doing those specific tasks.


[3001] Donohue, S., James B., Eslick A., & Mitroff S. (2012).  Cognitive pitfall! Videogame players are not immune to dual-task costs. Attention, Perception, & Psychophysics. 74(5), 803 - 809.

Choosing when to think fast & when to think slow

I recently read an interesting article in the Smithsonian about procrastination and why it’s good for you. Frank Partnoy, author of a new book on the subject, pointed out that procrastination only began to be regarded as a bad thing by the Puritans — earlier (among the Greeks and Romans, for example), it was regarded more as a sign of wisdom.

What babies can teach us about effective information-seeking and management

Here’s an interesting study that’s just been reported: 72 seven- and eight-month-old infants watched video animations of familiar fun items being revealed from behind a set of colorful boxes (see the 3-minute YouTube video).

How working memory works: What you need to know

Working memory is at the core of how we reason, understand, and remember.

Working memory capacity is now thought to be limited to four items, of which only one can be attended to at any one time.

Differences in working memory capacity probably have a lot to do with our well we form our memory codes — our skill in leaving out irrelevant material, and our skill at binding together the important stuff into a tightly-bound cluster.

Our ability to do this may decline as we age.

Factors that make some tasks more difficult than others include:

  • how often we have to shift our focus,
  • whether information already in focus has to be altered and how much time and effort is needed to change it, and
  • how complex the information is (how difficult it is to craft it into a tightly-bound cluster).

A New Yorker cartoon has a man telling his glum wife, “Of course I care about how you imagined I thought you perceived I wanted you to feel.” There are a number of reasons you might find that funny, but the point here is that it is very difficult to follow all the layers. This is a sentence in which mental attributions are made to the 6th level, and this is just about impossible for us to follow without writing it down and/or breaking it down into chunks.

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