How to Multitask

who can remember life before multitasking? These days we all do it: mothers, air-traffic controllers, ambidextrous athletes, high-flying executives who manage to eat, take conference calls, write e-mail and conduct board meetings all at the same time. We lionize those who appear to multitask effortlessly and despair at our own haphazard attempts to juggle even two tasks, secretly wondering if there exists a race of superior beings whose brains are hard-wired for multitasking feats. Only recently have neurologists begun to understand what our brains are up to when we do it. What they’ve learned offers hope to all multitasking delinquents out there.

1. Don’t think you can actually do two things at once. Even when you think you’re doing more than one thing simultaneously — say, driving and talking on a cell phone — you aren’t. Unlike a computer, the brain isn’t structured as a parallel processor. It performs actions, even very simple actions, in a strict linear sequence. You must complete the first task, or part of that task, before moving on to the next. What we call multitasking is actually task switching.

Hal Pashler, a professor of psychology at the University of California at San Diego, conducted an experiment in which he tested the brain’s ability to respond to two different sounds in quick succession. What he found is that the brain stalls fractionally before responding to the second stimulus. The second sound is heard (the brain can take in information simultaneously), but it requires time, if only milliseconds, to organize a response. “When you really study precisely what people’s brains are doing at any moment, there’s less concurrent processing than you might think,” Pashler explains. “The brain is more of a time-share operation.” He adds, “When fractions of a second matter, we’re better off not doing another task.”

2. Prioritize. To know when to switch tasks, you must distinguish between the tasks you must perform and those you can afford to blow off.

Consider the experiment that Jordan Grafman developed at the National Institute of Neurological Disorders and Stroke (N.I.N.D.S.) in Bethesda, Md. It’s a driving simulation in which you must avoid errant cars and jaywalkers, all while reciting sequences of numbers called out to you. Typically, your driving skills will grow more erratic as you pay attention to the numbers (although, frighteningly, you may not be aware of this). But when a virtual pedestrian dashes into the road, you’ll most likely abandon the recitation. That’s because in a driving simulation, avoiding killing people is the one challenge that outranks all others.

Before approaching multiple tasks, recommends Grafman, clearly establish which tasks are more important than others. “Mentally rehearsing,” he says, “definitely improves performance.”

3. Immerse yourself in your immediate task, but don’t forget what remains to be done next. To switch tasks successfully, the brain must marshal the resources required to perform the new task while shutting off, or inhibiting, the demands of the previous one. At the same time, you must maintain the intention to break off at a certain point and switch to another activity. During such moments of mental juggling, a section of the brain called Brodmann’s Area 10 comes alive. (Area 10 is located in the fronto-polar prefrontal cortex — at the very front of the brain.)

The crucial role played by Area 10 in multitasking was documented in a 1999 study that Grafman helped conduct; the results were published in the journal Nature. Functional magnetic resonance imaging scans (functional M.R.I.’s) were given to subjects at the Institute of Neurological Disorders while they performed simple multitasking experiments. Blood flow to Area 10 increased when people kept a principal goal in mind while temporarily engaged in secondary tasks. “This is presumably the last part of the brain to evolve, the most mysterious and exciting part,” Grafman says. “It’s what makes us most human.”

Paul Burgess, who researches multitasking at University College, London, has also been focusing on the role of Area 10. “If you’re missing it due to injury or a birth defect,” he explains, “you keep forgetting to do things.” He points out that successful multitasking requires that you not continuously think about switching tasks. That is, the activation of Area 10 does not require constant, conscious rehearsing of the need to switch tasks. For instance, if you have to make an important phone call at the end of the day, you don’t tend to make an explicit mental note of this fact every five minutes. Rather, you engage in a less explicit act of remembrance — a kind of low-level arousal, Burgess speculates, in which blood flow increases to Area 10.

4. Depend on routines — and compare new tasks with old ones. Multitasking becomes easier, scientists believe, when you make parts of the process routine. For example, driving, a familiar activity for many of us, becomes largely automatic — the parts of the prefrontal cortex involved in cognition surrender to the regions deeper in the brain that govern visual and motor control. Once a task has been learned, the brain will try to shift the load for performance to its deeper structures, freeing up the cortex for other tasks requiring active cognition. That way, if something unexpected happens (like a pedestrian bolting into the road), you’ll have the resources to deal with it.

When you are thrown into a new task, it’s helpful to search for a comparison to something you’ve done before. The brain thrives on analogies. If you’re suddenly forced to fly a crashing plane, you might want to draw on your PlayStation skills. “We solve task-switching dilemmas by trying to retrieve similar circumstances, similar situations being represented in similar regions of the prefrontal cortex,” Grafman says. “If we don’t, our experience will be totally chaotic, and we will clearly fail.” He then laughs. “This cannot explain Art Tatum.” The jazz pianist’s wild two-handed improvising was pouring from his CD player when I entered his office. “With Tatum, nothing was routine. He must have had a great prefrontal cortex.”

5. Make schedules, not to-do lists. And whatever you do, don’t answer the phone. For those of us who find multitasking difficult, Burgess claims that the simplest aids — like timers and alarms — are the most effective. When the American astronaut Jerry Linenger was working aboard the space station Mir, he wore three or four watches with alarms set to notify him when to switch tasks.

“The alarm does not have to carry any information, just be a reminder that something has to be done,” Burgess says. Studies have shown that neurologically impaired patients have been helped at multitasking by nothing more than someone clapping their hands at random intervals. An interruption breaks your train of thought and initiates a recall of what else needs to be done.

It’s important, however, that the interruption itself not entail a task. For example, if the phone rings, don’t answer it. Dealing with whatever the call is about will distract your brain from what you’ve already set out to do. Instead, use the interruption to see if you’re on track with other activities. “Make calling others one of the things that needs to be scheduled,” Burgess advises. “And if you have to answer the call, don’t go straight back to what you were doing before the call arrived. Very deliberately check the time, and ask yourself if there was something else you should have been doing.”

By following such an approach, you can actually change your brain. Visualizing the circumstances in which you need to switch tasks will establish a mental pathway that will be available when you really need it. As functional brain scans suggest, just by thinking about what we need to do and when we need to do it, we can increase blood flow to Area 10, our multitasking hot spot.

Age also improves us. Children are easily distracted from tasks by competing signals, and younger adults, with their maturing prefrontal cortexes, are best at learning and combining new tasks. As we age (and our brains atrophy), learning new tasks becomes harder, but we get better at extracting themes and prioritizing tasks.

“For tasks performed in a short period of time, the younger tend to do better,” Burgess says. “Older people learn from their mistakes and begin to compensate over time. This is very encouraging science for those of us not 20 years old.”

Catherine Bush is the author of the novel “The Rules of Engagement.”

Visible Bottleneck I

Q: OK, I tried it. What does Visible Bottleneck I show?

· Presumably you found it impossible to keep both bars from rising up when you tried to perform both tasks at the same time. So does everyone else as far as we know. This illustrates that one cannot normally carry out two tasks completely independently when each of them requires a choice of response. When we try to do so, substantial delays occur in one or both tasks. This is true even when neither task is anything that would be described as mentally challenging.

Q: How does the demo work?

· Each bar rises at a pre-set rate. A correct response in the relevant task lowers the bar by a certain amount. An incorrect response raises it. Thus, to keep it from rising to the top, you must respond both quickly and accurately. The parameters have been adjusted so in the single-task situation most people can keep the bar from rising, or even drive it down to the floor. In the dual-task situation, the parameters stay the same as in the single-task situations; the only difference is that you need to do both tasks simultaneously. If you could do both tasks in parallel at full speed, you should experience no great difficulty. (To verify that the difficulty of the two tasks is unchanged, try having someone sit down with you at your computer and do one of the tasks while you do the other. That’s a lot easier, isn’t it?)

Q: What causes this interference?

· Much research in this area argues that one particular mental operation is almost invariably carried out sequentially in tasks like this: the planning of responses. The same is true of certain types of decision operations and memory retrievals. On the other hand, the brain seems capable of perceiving stimuli while it is choosing a response, and actually producing motor responses in one task can overlap with the choice of a response in another.

Q: Where can I read more about this phenomenon?

· This article provides an overview.

zQ: Are all tasks requiring a choice of responses subject to this sort of processing bottleneck?

· Tasks that involve extremely “natural” mappings between stimuli and responses appear not to be. For example, repeating words aloud as you hear them is a task most people can carry out in parallel with other tasks (McLeod & Posner, 1984). The same is true of moving your eye to look at a spot (Pashler, Carrier & Hoffman, 1993). There may be others. Pressing a button depending on the spatial location of a disk (as in Visible Bottleneck II) may also bypass this bottleneck.

Q: What is the neural basis for this bottleneck?

· No one really knows, although some people have recently offered speculations, e.g. R. Marois & Colleagues.

Q: Are you saying people can only do one thing at a time?

· Not at all. If one of the tasks does not involve a choice of responses (e.g., if it merely involves repetitive rhythmic tapping, or requires perceiving and identifying stimuli without the need to decide on responses), interference is often reduced or even absent (subsequent demos on this site will illustrate this point). Laboratory experiments in which response times are analyzed in detail have lent considerable support to the idea of a “central bottleneck” in response planning and indicated that other operations are often processed in parallel between the two tasks (for recent reviews, see H. Pashler, The Psychology of Attention, 1998, MIT Press; P. Jolicoeur, Journal of Experimental Psychology: Human perception and Performance, 1999, 25, 596-616).

Q: When was a bottleneck in response planning first suspected?

· A slowing when people must respond to two stimuli presented in rapid succession was first observed by Telford in 1931. Several psychologists in the UK, including Margaret Vince and Kenneth Craik made related observations in the 1940s. Alan Welford was the first to specifically claim that the brain is subject to a single-channel bottleneck arising in the selection of responses.

Q: Does this Visible Bottleneck I demo have any scientific significance or is it just a demonstration?

· It may have some. In most laboratory studies of dual-task performance, the subject performs two discrete tasks in rapid succession (the so-called “psychological refractory period” experiment). A few psychologists have argued that dual-task slowing there may reflect voluntary postponement of processing, not a basic performance limit of the brain. They propose that subjects postpone selecting responses when presented with a pair of discrete tasks in order to make sure they do not respond in a reverse order. Whether or not that is plausible in the laboratory tasks, with the Visual Bottleneck applet there is a strong incentive for the subject to ignore response order completely, and process the tasks independently if that is possible. After all, if you could perform the two tasks independently, you would keep the bars from rising. This does not seem to happen.

Also, other psychologists have suggested that the slowing found in the discrete laboratory experiments just described might reflect the abrupt nature of the stimuli used in those tasks. Perhaps the brain can process two tasks at the same time, they argue, but one task would need to be performed for a few seconds before this capability would emerge. The present demo seems to indicate that this is not a critical factor (if you try getting one task going and then adding in the other task you will find that it doesn’t help much). Thus, this simple applet has some relevance to current controversies in the field of human attention research.

Q: Has this rising-bar task ever been studied in the laboratory?

· Not so far as we know. Related studies were performed by Kalsbeek and colleagues (1967) and Gladstones and colleagues (1989), however. They didn’t have bars, but they did examine the rate of performance of two tasks. Both groups interpreted their results as favoring the idea of a central bottleneck.

Q: What would happen if one practiced this task for a long time? Would it become “automatic” so I could keep both bars down?

· One thing that would be certain to happen is that you would get much faster even at the single-task performance. If the parameters were kept as they are, you would find it easier and easier to drive the bar down to the floor in the single task situation. The interesting question is what would happen if the rate at which the bars move up were increased as you got better, keeping the single-task situation equally challenging. What would happen then in the dual-task situation? Would performance fail catastrophically? We don’t know yet, but we hope to find out.

Q: Does this kind of research have any practical implications?

· The fact that there are severe limitations in our ability to perform certain mental operations simultaneously, even when the tasks appear simple and don’t involve the use of the same body parts, has obvious implications for issues like the safety of driving while using cellphones. More generally, a better understanding of dual-task performance should be helpful in interface design for any activity where rapid performance can be important, such as in aviation as well as the use of automobiles. Distraction appears to be a factor in many accidents, so a better understanding of attention limits should be useful.

Q: I had no trouble keeping both bars down!

· Really? Please contact us.