Is Multitasking Bad for You? The Real Cost of Switching

Picture a simple laboratory task. Numbers or shapes appear on a screen, one at a time. Sometimes you have to classify them by one rule, sometimes by another. The tasks are easy. Nobody fails them.

And yet, on the trials where the rule changes, something measurable happens. Your response is slower, and usually a little more likely to be wrong, than on the trials where you simply repeat what you did before. Psychologists call this the switch cost, and it is one of the most reliable findings in the study of attention.

That small, stubborn delay is the honest core of the debate about multitasking. The rest of the debate - including some very famous headlines - rests on much weaker ground. It helps to separate the two.

What happens when you switch

Most of what we call multitasking is not doing two things at once. For anything that needs thought, the mind mostly alternates: a line of an email, a glance at a message, back to the email. Each alternation has a price.

In 2001, Joshua Rubinstein, David Meyer and Jeffrey Evans ran four experiments in which people either repeated one task or alternated between two. Some tasks involved sorting geometric shapes by different rules; others involved solving arithmetic problems with different operations. Alternating produced a time cost every time. That cost grew when the rules were more complex, and it shrank when people were given a visual cue about which task came next.

Their interpretation was that switching involves at least two stages of mental control: shifting the goal (now I am doing this, not that) and activating the rules for the new task. Both take time, and neither happens for free just because you want it to.

Preparation helps, but not completely

In a widely cited 2003 review, the psychologist Stephen Monsell summarised what years of these experiments had shown. Immediately after a task switch, responses are substantially slower and usually more error-prone. Giving people time to prepare for the switch reduces this cost - but does not eliminate it.

Monsell described the cost as coming from several sources at once. Part of it is the time needed to reconfigure your mental set for the new task. Part of it is leftover activation from the old task that has not fully faded, and leftover inhibition that you applied to the new one while you were busy with the old. In everyday terms: when you come back to a report after answering a message, some of your mind is still in the message.

A reasonable caution is that these are milliseconds on simple tasks in a lab. Nobody has turned them into a reliable figure for how much of a working day is lost to switching, and you should be sceptical of precise percentages you see quoted. What the lab work does show is the direction and the mechanism: switching is never free, and it costs more when the tasks are complex.

The heavy multitasker headlines

In 2009, Eyal Ophir, Clifford Nass and Anthony Wagner published a study that became one of the most quoted in the field. They built a questionnaire to measure how often people use several media at once - say, messaging while watching video - and compared heavy and light media multitaskers on standard tests of mental control.

The results were striking. Heavy media multitaskers were more easily distracted by irrelevant things in their environment and by irrelevant information in memory. Most surprisingly, they were also worse on a test of task switching, the very skill you might expect them to have practised. The authors suggested this came from a reduced ability to filter out interference.

The idea that multitasking makes you worse at multitasking was irresistible, and it travelled far beyond the original paper.

What happened when others tried to replicate it

Later studies did not all agree. In 2017, Wisnu Wiradhany and Mark Nieuwenstein ran two replication studies with a total of 14 tests, designed with reasonable statistical power to detect the original effects. Only five of the 14 showed a significant effect in the expected direction, and only two of those survived a more conservative analysis. Their meta-analysis of 39 effect sizes found a weak association between media multitasking and distractibility, which became non-significant once they corrected for the tendency of small studies to report bigger effects.

A 2018 review by Melina Uncapher and Anthony Wagner - one of the original authors - took a more positive but still careful view. On balance, they wrote, heavier media multitaskers tend to perform worse in a number of cognitive areas, especially tasks that need sustained attention, although many studies find no difference at all. They were explicit that the direction of causality is unknown.

A 2021 meta-analysis by Douglas Parry and Daniel Le Roux, pooling 118 assessments, found a small overall association that depended heavily on how multitasking and attention were measured. Their conclusion was blunt: a decade on, researchers were no closer to understanding the link.

That last point matters. Even where the association exists, it is a correlation. People who are easily distracted may be drawn to multitasking, rather than multitasking making them distracted. The evidence does not yet tell us which.

What this means for you

The robust finding is the modest one: each switch costs something, the cost grows with task complexity, and preparing for a switch helps but does not remove it. The dramatic claim - that multitasking permanently damages your attention - is not established.

If you are curious about your own habits, our absent-mindedness test, our mind-wandering test and our phone habit test can help you notice patterns. They describe tendencies; they do not measure brain damage or diagnose anything.

Some practical ideas follow directly from the lab work:

• Batch similar tasks. Answering ten messages in one block means one switch, not ten.
• Protect complex work. Because switch costs grow with rule complexity, the tasks that suffer most from interruptions are the hard ones. Give those uninterrupted time first.
• Leave yourself a cue. Cues reduced switch costs in the experiments. A one-line note about what you were about to do next makes returning to a task easier.
• Reduce involuntary switches. Notifications are switches you did not choose. Turning off the ones you do not need is the simplest change available.

None of this requires believing that your brain has been rewired by your phone. It only requires accepting a smaller, better-supported truth: attention is a limited resource, and every jump spends a little of it.