Are we really good at multitasking?

Over the past several years, research has helped us better understand what happens when we try to manage several tasks at once. Rather than suggesting that multitasking is impossible, these studies show that our ability to divide attention has limits — particularly when the tasks require concentration, decision-making or active processing.

Attentional blink

In 2005, Sergent, Baillet and Dehaene examined the brain mechanisms involved in what is known as the attentional blink.

The phenomenon can be compared to a brief mental “blink”: a temporary and unconscious lapse in attention that can occur when our focus shifts quickly from one piece of information to another. During this short interval, some information may be more easily missed than when our attention remains focused on a single task.

Their research showed that the brain needs a certain amount of time to process sensory information before it can be consciously registered and used. When information arrives in very quick succession, some of it may not receive the same level of attention.

This is also related to the concept of attentional flexibility — our ability to engage attention, disengage from one task and then successfully re-engage with another. This ability varies depending on the individual, the situation and the types of tasks involved.

What neuroimaging tells us about doing two things at once

In 2010, Inserm researchers Sylvain Charron and Étienne Koechlin used neuroimaging to observe the brain activity of participants performing multiple tasks.

Their study suggested that the brain may be able to manage two concurrent goals by distributing activity across the frontal lobes. When participants focused on a single task, both frontal lobes were involved. When a second task was introduced, the activity became more divided.

The situation became more difficult when participants were asked to manage a third task.

They were more likely to overlook one of the tasks and made more errors than when they were managing two. These findings suggest that there may be practical limits to how many active goals we can manage efficiently at the same time.

Multitasking may also require additional mental effort. According to MIT neuroscientist Earl Miller, repeatedly shifting attention between tasks can place extra demands on the brain and may affect efficiency.

Could we handle a third task?

The findings from Charron and Koechlin do not necessarily mean that the human brain is incapable of performing more than two activities at once.

Neuroscientist Scott Huettel of Duke University has pointed out that much depends on the nature of the tasks involved. In an interview, he noted that highly practiced or largely automatic activities can often be combined more easily with other tasks.

Eating, for example, relies on well-practiced motor skills that may not compete heavily with the brain systems involved in language, visual interpretation or more complex cognitive activities.

In other words, some combinations of tasks are easier to manage than others. Walking while having a conversation, for instance, is very different from writing an important email while trying to follow a complicated discussion and review a spreadsheet at the same time.

More demands can mean more mistakes

A 2016 study examining task-switching in emergency medicine looked at professionals who regularly have to move rapidly between tasks in an environment where interruptions are common.

The research suggests that, unless a task has become highly familiar or automated through practice, increasing the number of competing demands on our attention can also increase the likelihood of errors.

This may help explain why familiar activities can sometimes be performed alongside another task with relatively little difficulty. With practice, certain behaviours become more automatic and require less conscious attention.

Interruptions can also make it harder to return immediately to the same level of concentration. Research by Gloria Mark and colleagues found that workers frequently switch between activities following interruptions, and that these disruptions can be associated with greater stress and a sense of increased workload (Mark et al., 2008).

Overall, what we commonly call “multitasking” often involves a combination of simultaneous activity and rapid switching between tasks. How successfully we manage it depends on many factors, including the complexity of the tasks, how familiar they are and how much attention each one requires.

So while answering messages during a meeting or moving between several projects may sometimes feel efficient, there can also be a cost in terms of concentration, speed or accuracy.

The takeaway is not that we should avoid multitasking altogether, but rather that some tasks benefit from our full attention — especially when they are complex, unfamiliar or important.