We live in the era of multitasking. According to a recent study, 81% of Americans always or almost always engage in at least one additional activity while watching television. When 200 people were asked to track their media activities during a one-hour evening period in another study, they reported switching between mobile phones, tablets, and laptops 21 times, and 95% of them did this with the television on for the entire hour.

We can’t help ourselves. We multitask at work, at the dinner table, in everyday conversations, while watching television, while driving our kids to school, even while having sex.

Some people may still believe multitasking is making them more effective, but the smart among us have long realized that single-tasking is the superior alternative. Let’s face it, we don’t multitask because we think it’s a good idea. We do it because we like the thrill of it, because concentrating is hard work, and, frankly, because we’re addicted to distraction.

It’s not a big deal, we tell ourselves. The costs of multitasking aren’t that big. If we really have to concentrate, we can.

Well, we might be horribly wrong. There’s abundant scientific evidence showing that the costs of multitasking aren’t trivial at all. Not only is our productivity at stake, but also our health, safety, relationships, and emotional well-being. Most shockingly, researchers refute the idea that we can just turn on our focus when we really have to.

What is Multitasking

When asked to define multitasking, people will describe a process of “doing two or more things at the same time,” which comes close to the official definition: “the performance of multiple tasks at one time.”

Upon close inspection, these definitions leave plenty of room for interpretation. For example, does “browsing the Web” qualify as a form of multitasking? On the one hand, browsing the Web is just one thing. On the other hand, it tends to include multiple tasks, such as reading articles or watching videos. If, while browsing the Web, you are switching between reading and watching, is that a form of multitasking?

What if you’re performing two tasks over a period of five minutes? Is that multitasking? It surely involves doing multiple tasks. But if you’re performing the first task for two minutes, followed by the second task for three minutes, that would be two minutes of single-tasking on one task and three minutes of single-tasking on the other task. What if we reduce the time increment and perform the two tasks in a 20-second window? Is that multitasking?

Researchers trying to study the effects of multitasking run into these very problems. That’s why the only constant across studies in this area is the fact that more than one task is performed in a given time period. Some researchers have participants literally perform two tasks at the same time, such as driving and holding a conversation. Others force subjects to switch between two tasks every couple of seconds, while yet others tell people to focus on one task while subjecting them to various distracting stimuli, such as background chatter.

For sake of simplicity, we will focus on the first two types of studies, which leaves us with two forms of multitasking:

Concurrent multitasking is when you literally try to perform two tasks at the same time, such as when you’re driving and holding a conversation, walking while writing a text message, or trying to compose an email while also following the plot of a TV show.

Sequential multitasking is when you perform two or more tasks in rapid succession and in sequential order, such as checking Facebook, then Twitter, then Instagram, then email, and then your favorite News website. It describes how the average knowledge worker behaves at their job, constantly switching between email, phone conversations, in-person conversations, and other tasks. 

For the brain, concurrent and sequential multitasking are actually the same thing. The only difference, as you’re about to see, is how often the brain switches between the respective tasks.

The Brain and Multitasking

When it comes to multitasking and the brain, the devil is in the details. On the one hand, our brains certainly perform countless unconscious and reflexive processes simultaneously – receiving and processing data from our sensory system, breathing, moving blood throughout the body, maintaining heart rate, or digesting food. However, these aren’t what we understand as multitasking.

On the other hand, when it comes to performing two non-reflexive, not fully automated tasks, the brain doesn’t actually perform them at the same time. Rather, what’s happening is that the brain rapidly switches between both tasks. A more appropriate term for everyday multitasking would therefore be task switching.

A brain scan study illustrates this beautifully. Researchers instructed participants to pay attention to a nature scene presented to them on a computer screen, and hold the details in mind over a 7-second delay period, after which they were tested on how well they remembered the scene. On some trials, they had to perform another task at the same time. While holding the scene details in mind, they had to make a gender and age decision about a face that flashed on the screen during the delay period.

The brain scans showed that certain brain regions were activated when participants performed the nature scene remembering task. For sake of simplicity, we can refer to these brain regions as the nature-scene-network. So when the participants only performed this task, the only brain region that activated was the nature-scene-network. When the second task was introduced, something fascinating happened. During the delay period – in which the face was flashed on the screen and participants had to make a decision on it – the nature-scene-network diminished (was less active). At the same time, a new network became engaged, a network for performing the second task, which we could call the face-decision-network.

Researchers have known for a long time that different brain networks activate for different tasks. However, what’s telling about this study is that both networks were not engaged equivalently at the same time. When the face-decision-network activated, the nature-scene-network de-activated. Likewise, when the short second task was over, its network diminished and the original network for the nature scene became re-activated.

Even though the researchers gave no instructions to participants to switch between the two tasks, that’s actually what their brains were doing. They do not maintain the network for one task when another task is introduced. Rather, they rapidly switch between the two cognitive networks.

In short, the brain doesn’t parallel process; it switches between tasks. So while we think we’re multitasking, the brain itself is task switching or network switching. Whether we’re talking about concurrent multitasking (performing two tasks simultaneously) or sequential multitasking (performing two or more tasks in sequential order) it’s actually the same for the brain. The only difference is in how often the brain is switching between the two activities.

Studies done on the effects of multitasking differ in the tasks involved (e.g., multitasking while studying or while driving a car) and in the frequency of switching (e.g., switching every few seconds or every few minutes). What all studies find is that the brain isn’t good at switching between tasks, and it loses time whenever it’s forced to switch. The more complex the tasks, and the more often the brain has to switch, the bigger the loss. And the loss in time isn’t the only cost incurred by frequent task switching. But I’m getting ahead of myself.

Multitasking and Productivity

To measure the effects of a brain rapidly switching between tasks, researchers perform task-switching experiments in their laboratories.

Although studies differ in details, the general framework is always the same. Participants perform two different cognitive tasks and are measured on how many errors they make and how much time they need to complete them. What changes is how often they have to switch between the tasks. Sometimes, they perform task A four times in a row before moving on to task B and performing that four times in row (AAAABBBB). Other times, they have to switch on every trial (ABABABAB) and yet other times on every second trial (AABBAABB).

A study from 1995 found that even when people knew ahead of time that they had to switch tasks on every second or fourth trial, they were still slower and made more errors on task-switch than on task-repeat trials. Even when the time between trials was increased, this did not fully eliminate the switching costs. Sure, participants did better when they had more time between tasks, but they did still worse than if they didn’t have to switch.

In a 2001 study, participants had to again switch between different cognitive tasks, such as classifying geometric objects or solving math problems. For all tasks, they lost time when forced to switch from one to another. As tasks got more complex, participants lost more and more time. Time costs also increased when participants switched to tasks that were relatively unfamiliar.

What these and other task-switching studies show is that every single time you switch, you waste a little bit of time. And although the cost of an individual switch may be small, sometimes just a few tenths of a second, the accumulated costs of frequent switching add up quickly, especially as tasks become more complex. According to Dr. David Meyer, one of the researchers in the 2001 study, “even brief mental blocks created by shifting between tasks can cost as much as 40 percent of someone’s productive time.”

Bottom line: The more often you switch, and the more complex the tasks involved, the more time you lose.

Knowing this, consider the average office worker’s day. According to a 2004 study, knowledge workers switch tasks an astonishing average of 20 times per hour. As the authors write, “In a typical day, we found that people spend an average of three minutes working on any single event before switching to another event. Informal interactions average four and a half minutes each. Further, people spend on the average somewhat more than two minutes on any use of electronic tool, application, or paper document before they switch to use another tool. The longest duration of tool use is with PCs, yet this averages only slightly more than three minutes at any one time.” A later study, published in 2016, found that the average online screen focus of information workers was a mere 40 seconds.

A similar study, this time with college students, found that task switching occurred on average every 48 seconds when participants were on their computers. This amounts to 1.2 switches per minute, or over 70 switches per hour. Even if switching costs are minor, it’s clear that productivity is lost.

Now, before we move on, let’s tackle the question of why switching costs occur in the first place. While there are many theories floating around, researchers haven’t agreed on a single one yet. What seems certain is that it involves two elements. The first one is cozying up with the new task (activating its “rules,” getting up to speed). The more complex this new task, the more time this process will take.

The second element is “forgetting” about the previous task. The more complex this previous task was, the higher the switching costs will be. One popular theory about this element involves the concept of attention residue, a term coined by Sophie Leroy. According to this idea, residues of your attention will linger with a previous task after making a switch. Instead of having 100% of your attention on the new task, you may only have 80% on the new task and the remaining 20% still on the old task.

We’ve all experienced extreme examples of this. After an intense fight with your spouse, some part of your attention will linger on this incident even as you’re trying to concentrate on a new task. In that example, the residue of attention would be large.

How long it takes for your attention to stop lingering on previous tasks and get fully focused on the new task is up for debate. Sometimes, it may be a few seconds or a couple of minutes. Other times, it may take 20 to 30 minutes. It all depends on the complexity and emotional attachment of the previous task.

The point is: Every time you switch between tasks, you lose time, and the more complex the tasks are, the more time you will lose. The more often we switch, the less productive we will be – this is the most basic and robust finding in the research. Multitasking makes us less productive, period.

Multitasking and Learning

In one lab experiment, students were randomly assigned to three groups to read a book chapter and take a comprehension test. The first group simply read the chapter and took the test. The second group first had an instant message conversation with the experimenter and then read the chapter and took the test. The last group were interrupted with the same conversation (delivered in pieces at various times during the reading) and then took the test – this simulated the typical behavior of college students. The results showed that all groups performed equally well on the test, but the interrupted group took substantially longer even when the time spent instant messaging was removed.

Considering what we know about switching costs, the result isn’t too surprising. I would even argue that students are aware that multitasking reduces their effectiveness. The reason they behave that way is either they’re bored and enjoy the stimulation created by the multitasking. Or they want to concentrate on studying, but can’t keep themselves from constantly checking their phones. Most likely, both are true.

Another study on multitasking and learning required students to use a specific technology – texting, emailing, social media, or instant messaging – while attending course lectures. All four multitasking groups, plus a group that was allowed to use any technology they wanted, performed worse on a test of the delivered content than those participants who didn’t use any technology during the courses.

Another study simulating normal-in-class behavior interrupted students during a video lecture and required them to either post material on social media or text the experimenter. One group had to post or text every minute, another group every thirty seconds, and a control group simply watched the video. The results showed that more social media posting and texting resulted in poorer lecture notes and lower test scores. And the effect was linear: the highest test scores and best lecture notes came from those students who did not receive any interruptions, the second best scores and notes from those students who were interrupted every minute, and the worst scores and notes from the students who were interrupted every 30 seconds.

Considering what we’ve learned about task-switching costs, none of these results are too surprising; they simply confirm what we already know. However, one study on multitasking and learning is a bit more alarming because it shows clearly that learning doesn’t just take more time, it’s also of worse quality when combined with other tasks. "Multi-tasking adversely affects how you learn," explains psychology professor and author of the study Russell Poldrack. "Even if you learn while multi-tasking, that learning is less flexible and more specialized, so you cannot retrieve the information as easily. Our study shows that to the degree you can learn while multi-tasking, you will use different brain systems.”

When you’re multitasking while learning, you recruit the wrong brain regions. Instead of relying on the hippocampus, you use the striatum. As a result, the learning will be less flexible. You won’t be able to extrapolate, to remember facts when placed in a different context. So not only are you wasting time when multitasking, you’re also unknowingly deceiving yourself. You may think you know the facts, but you won’t be able to recall them in a new context. Poldrack’s advice: "The best thing you can do to improve your memory is to pay attention to the things you want to remember… Concentrate while you're studying.”

Multitasking and Stress

If you are constantly being pulled in multiple different directions, trying to do several things all at once, wouldn’t it make sense that you’ll feel more stressed? Let’s see.

A 2014 study logged computer activity and used biosensors to measure stress levels of 48 college students as they went about their lives for 7 days for all waking hours. The first thing the study found was that multitasking behavior was through the roof for these people. When they were on their computers, the average time on any window (before switching to another window) was a mere 48 seconds. They switched over 70 times per hour.

The study also found that the more time students spent on the computer and the higher their window-switching frequency, the higher was their stress. That said, there’s once again the issue of causation. It’s impossible to tell whether multitasking, or computer usage for that matter, actually caused the stress. Maybe the stressed out students switched more and spent more time on the computer because they were on a deadline.

Another study explored work interruptions and their effects on stress. It was found that interrupted work was actually performed faster than non-interrupted work, but it came at a price. As the authors explain, “people in the interrupted conditions experienced a higher workload, more stress, higher frustration, more time pressure, and effort.” The interpretation is that “when people are constantly interrupted, they develop a mode of working faster (and writing less) to compensate for the time they know they will lose by being interrupted.”

While these studies hint at interesting associations between stress and multitasking, they don’t prove that multitasking in and of itself is actually causing stress. Does multitasking release stress hormones in the brain like some researchers claim? We don’t know.

Multitasking and Safety

In 2011, Cathy Cruz Marrero rose to fame after a video of her walking in a mall while texting on her phone and then falling headfirst into a fountain went viral. Such accidents are on the rise. According to one report, 559 people in the US had hurt themselves by walking into a stationary object while texting in 2004. By 2010 that number rose to over 1,500, and estimates by the study authors predicted the number of injuries to double between 2010 and 2015.

Research shows that using a phone while walking modifies the walker’s step width, step length, toe clearance, and walking cadence and makes them more prone to injuries. In one study, people who were texting or listening to music were more likely to be hit by a simulated car.

While we can probably all laugh at people who sustain minor injuries while walking and using a smartphone, things get more serious when we move from “walking” to “driving.” According to the US National Safety Council, an estimated 23% of all car crashes involve cell phone use. A large number of behavioral studies now prove that performing another cognitive task while driving an actual or virtual vehicle substantially degrades driving performance.

Contrary to popular belief, it doesn’t matter if phone conversations are being held hands-free or not. A meta-analysis of dual-task driving studies concluded that the costs to driving performance resulting from a secondary simulated conversation task were equivalent for hand-held and hands-free devices. They also concluded that the literature suggest a large overall decrement in driving performance when a secondary task is added.

An interesting study from 2008 sheds a light on why cell phone use during driving is so detrimental. Participants used a driving simulator to steer a car along a winding road while having their brains scanned in an MRI scanner. In one condition, participants were performing the driving task and a simultaneous listening comprehension task, in which sentences referring to world knowledge had to be judged as true or false. In the control condition, participants only performed the driving task.

The results showed that in the multitasking condition there was much less brain activation (approximately 37%) associated with the driving task than when the driving task was performed alone. This reduced activation was accompanied by a decrement in driving performance, as measured by poorer lane maintenance and more frequent hitting of the berm. When performing another task while driving, the brain is forced to perform the kind of network switching we discussed earlier. In this case, the brain was rapidly switching between the driving network and the listening network. As a result, the driving network experienced an overall reduction in activation of 37%, which then resulted in worse driving performance.

Bottom line: If you care about the safety of yourself and your fellow passengers, stop using your phone in any way while you’re driving. You can still talk to your passengers, as that has not been shown to decrement driving performance. The difference between talking on your phone or talking to passengers is that passengers act as another set of eyes that help you control the vehicle, which is not the case with people on the phone.

Multitasking and Social Interactions

We know from positive psychology research that social relationships are the #1 driver of happiness. Daniel Gilbert, one of the leading researchers in this field, puts it well: “We are happy when we have family, we are happy when we have friends and almost all the other things we think make us happy are actually just ways of getting more family and friends.”

But what happens to our social relationships when we stop paying attention to our friends and family? When, instead, we constantly look at our phones? There’s little research on this topic, but a few studies start shedding a light on the potential negative effects of multitasking during social interactions.

One experiment examined the impact of having a phone present during an interpersonal social setting. In two face-to-face studies, researchers had two strangers have either a casual conversation or discussing meaningful personal matters. In one condition, a mobile phone – not belonging to either of the participants – was placed on a nearby table within full view but not in direct line of sight of either one. In the control condition, the phone was absent and replaced by a similar-size notebook. After the short conversation, both participants rated their feelings of trust, empathy, closeness, and understanding with the their partner. The results showed that the mere presence of the mobile phone inhibited the development of interpersonal trust and closeness, and reduced the extent to which individuals felt empathy and understanding from their partners.

A similar study compared conversations between strangers while they were either having their phones on the table or in their hands or while phones were absent. The results showed that in the presence of phones conversations were rated as less satisfying and were reported as generating less empathic concern. Such findings are now referred to as “the iPhone effect.”

I used to take my phone out of my pocket and put it on the table during meals or when I was on the computer or studying. I no longer do because, clearly, the mere presence of a mobile device is enough to distract us in unexpected ways. To protect myself from the radiation emitted by the phone, I simply put it on airplane mode most of the time.

Multitasking and Psychological Well-Being

Some people claim that multitasking increases depression and social anxiety. While there is certainly a link between these psychological disorders and multitasking, there is not yet proof of causation. One often cited study showed that “increased media multitasking was associated with higher depression and social anxiety symptoms, even after controlling for overall media use and the personality traits of neuroticism and extraversion.”

If you take a second to think about this, doesn’t it make sense that depressed and socially anxious people use media multitasking as a way to distract and numb themselves? In fact, that’s exactly what I would expect these people to do. Now, would they be better off, less depressed, and less socially anxious if they engaged in different behaviors, e.g., exercise, meditation, or dinner with friends? Sure. But that doesn’t mean that media multitasking itself increases depression and social anxiety. So, is multitasking harming your emotional well-being? We don’t know yet.

Are There Benefits to Multitasking?

Indeed, there is one thing multitasking has to offer: It can make boring and aversive activities more enjoyable. You may not feel like doing the dishes, but if you can listen to some music or a television show while doing it, that may just help you to gather enough discipline to get it done.

This is sometimes called temptation bundling, a technique coined by Katy Milkman, a professor at The Wharton School of Business. She defines it as “combining a temptation — something like a TV show, a guilty pleasure, something that will pull you into engaging in a behavior — with something you know you should do but might struggle to do.” You bundle a behavior you should do with a behavior you feel tempted to do.

This is pretty much the only form of multitasking I support and engage in regularly. I watch Game of Thrones while eating dinner, watch YouTube videos while clipping my nails, listen to podcasts while going for walks, listen to music while doing mundane business tasks, or watch videos while hanging the laundry.

This “benefit” is, of course, a double-edged sword. The fact that multitasking is more rewarding to our brains than single-tasking is the very reason we engage in so much multitasking in the first place. Oh well, productivity demands that we be selective about when we allow ourselves to enjoy the pleasures of multitasking and when not.

Are There Long-Term Effects of Multitasking?

Time to get serious. You may still feel optimistic about your multitasking behavior. Sure, it’s making you less productive, less safe, impairs your learning, and lowers the quality of your social interactions. But it’s fun, single-tasking is a bore, and you don’t like the hassle of trying to change your behavior. Besides, if you really have to concentrate and get something done efficiently, you can. There’s no harm in having a bit of multitasking fun, right?

Sorry, but you might be gravely mistaken. A 2009 study divided people into heavy media multitaskers* and light media multitaskers, and compared their performance on a variety of cognitive tests. It was found that heavy multitaskers had less control over their working memory, were more easily distracted by irrelevant stimuli, and were less able to maintain focus on any given task.

*(In that study, media multitasking is defined as “a person’s consumption of more than one item or stream of content at the same time.” This definition is different from the one we’ve used in this article. For example, listening to music while writing an email would qualify as media multitasking, while it wouldn’t qualify as multitasking per our definition. The results are nonetheless eye-opening.)

Anthony Wagner, one of the study authors, commented about heavy multitaskers, “when they’re in situations where there are multiple sources of information coming from the external world or emerging out of memory, they’re not able to filter out what’s not relevant to their current goal. That failure to filter means they’re slowed down by that irrelevant information.” Fellow researcher Eyal Ophir added, “They couldn’t help thinking about the task they weren’t doing. The high multitaskers are always drawing from all the information in front of them. They can’t keep things separate in their minds.”

The lead researcher of the study, Clifford Nass, paints an even bleaker picture, calling heavy multitaskers “suckers for irrelevancy” who are “distracted by everything.” In an interview about his research, he said that “people who chronically multitask show an enormous range of deficits. They're basically terrible at all sorts of cognitive tasks, including multitasking… People who multitask all the time can't filter out irrelevancy. They can't manage a working memory. They're chronically distracted. They initiate much larger parts of their brain that are irrelevant to the task at hand. And even - they're even terrible at multitasking. When we ask them to multitask, they're actually worse at it. So they're pretty much mental wrecks.”

He continued, saying that heavy multitaskers have “developed habits of mind that make it impossible for them to be laser-focused. They're suckers for irrelevancy. They just can't keep on task.” When asked if multitasking had caused these people to lose their ability to focus on one thing, he emphatically agreed, “That's precisely right. Our brains have to be retrained to multitask and our brains, if we do it all the time - brains are remarkably plastic, remarkably adaptable. We train our brains to a new way of thinking. And then when we try to revert our brains back, our brains are plastic but they're not elastic. They don't just snap back into shape.”

Perhaps most fascinating, Nass explained that multitaskers believe themselves to be incredibly productive. He said that it might be possible to retrain these people’s ability to concentrate by, for example, forcing them to ditch multitasking for a few weeks – but the heavy multitaskers flat out refused to do it. 

Since that preliminary study, others have followed. A 2017 study, aptly titled I Want to Media Multitask and I Want to Do it Now, does a nice job at summarizing the findings. In short, heavy media multitaskers have increased self-reported mind-wandering and more everyday lapses of attention, greater self-reported impulsivity, increased distractibility, reduced self-control, reduced attentional control, and reduced ability to delay gratification – compared to light media multitaskers. One study even found that heavy multitaskers have reduced gray matter density in a brain region called the anterior cingulate cortex, though researchers do not yet know the implications of this finding.

Now, before you freak out completely, let’s make it clear that no causation has been proved yet. These are only correlational studies. It could be that individuals with higher distractibility, reduced self-control, or greater impulsivity are simply more likely to engage in media multitasking. In fact, this is most likely the case. However, it is also possible that frequent multitasking creates the aforementioned changes (increased mind-wandering, more lapses of attention, etc.).

We also don’t know how different types of multitasking affect the brain differently. How many tasks are involved? What kind of tasks? How many media streams are involved? What type of media? How often is the brain forced to switch? These are all aspects that would result in different results.

What we do know is: Human brains are plastic. Our environment and behavior change the very structures of our brains in a process of adaptation. We also know that attention spans have continuously decreased over the past decade. And we would probably all agree that our ability to concentrate and focus on one thing has taken a hit. How much of a role multitasking has played in these changes remains to be seen.

So, where does that leave us?

Conclusion

Our good ol’ friend Anonymous once said “multitasking is the art of screwing up several things at once.”

Multitasking lowers your productivity, impairs learning, creates stress, endangers your safety, and reduces the quality of your social interactions. Worse yet, chronic multitasking is associated with everything from greater impulsivity, increased distractibility, increased mind-wandering, reduced self-control, reduced ability to delay gratification, increased depression and anxiety, and more.

It’s a fool’s game: Trading temporary pleasure for long-term success. Personally, I try to keep multitasking to a minimum. My strategy for maximizing productivity is similar to Cal Newport’s idea of deep work: Work on a single task, uninterruptedly, for a long period of time, with as much focus as you can muster.

About the only form of multitasking I succumb to on a regular basis is temptation bundling – watching Netflix while eating dinner, listening to music while dispatching boring tasks, watching YouTube videos while hanging the laundry.

If I had the discipline, I would take it a step further and follow Eknath Easwaran’s advice “to abandon totally my habit of trying to perform several operations simultaneously.”