Can People Really Multitask? The Cost of Switching and How to Live With It

Of 200 people tested, 2.5% could do two things at once with no drop in performance at all. The study, by Watson and Strayer at the University of Utah, was published in Psychonomic Bulletin & Review in 2010.

Participants drove in a high-fidelity driving simulator while answering a demanding memory task presented by ear. Their scores were compared with driving alone and with the memory task alone. The vast majority did clearly worse at both when they had to do them together. The authors called the 2.5% who showed no decline “supertaskers”. Even when doing one task at a time, these people scored in the top quarter on every measure.

So for almost everyone, multitasking badly is normal. This post looks at why performance drops when we do two things at once, and what happens in the mind when we switch from one task to another.

Doing two things at once, and switching

Research on multitasking has two main strands. One studies dual tasks: doing two tasks at the same time, or with almost no gap between them. The other studies task switching: moving back and forth between tasks, in a fixed order or when a cue says so.

A 2018 review in Psychological Bulletin by Koch and colleagues points out that these two strands grew up largely apart, with different methods. It also notes that many studies have found performance drops when people have to handle several tasks or actions, compared with suitable control conditions.

The bottleneck in doing two things at once

Start with doing two things at once. A 1994 review by Pashler, also in Psychological Bulletin, opens with the observation that people often have trouble performing two fairly simple tasks at the same time.

On the cause, the review concludes that there is a stubborn bottleneck in the process of choosing an action, and probably in retrieving things from memory in general. Like the narrow neck of a bottle, it is a stage two tasks cannot pass through at the same moment. Separate kinds of interference, the review adds, also come from preparing for a task, from seeing and hearing, and from timing.

In other words, even when we feel we are doing two things in parallel, at some stage one task may be waiting for the other.

The cost of each switch

Now switching. A 2003 review in Trends in Cognitive Sciences by Monsell of the University of Exeter starts from the fact that everyday life requires frequent shifts between tasks.

In this research, participants are given a small set of simple tasks and switch among them often. Right after a switch, they respond much more slowly than when they repeat the same task, and they usually make more errors. This is called the switch cost.

A chance to prepare for the next task makes the switch cost smaller, but it does not make it go away. Monsell traces the cost to two sources: the mental setup for the previous task lingering, or being held down, after the switch; and the time it takes to reconfigure for the new task.

What makes a switch heavier

Not every switch costs the same. A 2001 paper in the Journal of Experimental Psychology: Human Perception and Performance by Rubinstein, Meyer and Evans looked at this in four experiments.

Participants sorted shapes by different rules, or solved arithmetic problems using different operations, either alternating between tasks or repeating one. The time lost to switching grew as the rules got more complex, and shrank when a visual cue showed which task to do next.

Switching from a familiar task to an unfamiliar one also seemed to take longer to load the rules than switching the other way. The authors explain the results with a model in which a switch has two stages: shifting the goal, and activating the new rules.

Living with the cost of switching

The tasks in these studies were simple ones, such as sorting shapes or doing sums. Even so, a few points carry over to daily work.

Fewer switches. If every switch has a cost, grouping similar work together cuts the number of switches. Answering email in one sitting rather than throughout the day is one example.

Knowing what comes next, with a moment to prepare. Time to prepare made the switch cost smaller, and a clear cue about the next task made switching faster.

Extra time for unfamiliar work. Going from a familiar task to an unfamiliar one took longer than the reverse. When such a switch is coming, that time can be planned in.

One task at a time when safety is at stake. The supertasker study used driving. Phone calls and crash risk behind the wheel are covered in Is a Hands-Free Phone Safe While Driving?

The effect of being interrupted mid-task, and “attention residue” from unfinished work, are covered with their studies in Can’t Stay Focused? A 10-Minute Daily Practice for Adults. Studies comparing people who often use several media at once, like TV and a phone, with people who rarely do are in Does Too Much Smartphone Use Hurt Your Focus?

Being bad at multitasking is normal

Of the 200 people, 5 showed no decline at all when doing both tasks together. The vast majority did clearly worse. The bottleneck in doing two things at once and the cost of each switch are not a weakness of a few people. They show up again and again across experiments as part of how human minds work.

If multitasking feels hard, that means your mind works the way most minds do. There is also a view that planning work so you can finish one thing at a time is a skill in its own right.

References

• Watson JM, Strayer DL. Supertaskers: Profiles in extraordinary multitasking ability. Psychon Bull Rev. 2010;17(4):479-485.
• Koch I, Poljac E, Müller H, Kiesel A. Cognitive structure, flexibility, and plasticity in human multitasking: An integrative review of dual-task and task-switching research. Psychol Bull. 2018;144(6):557-583.
• Pashler H. Dual-task interference in simple tasks: Data and theory. Psychol Bull. 1994;116(2):220-244.
• Monsell S. Task switching. Trends Cogn Sci. 2003;7(3):134-140.
• Rubinstein JS, Meyer DE, Evans JE. Executive control of cognitive processes in task switching. J Exp Psychol Hum Percept Perform. 2001;27(4):763-797.

BrainDojo has trainings called Dual Task and Triple Task. In Dual Task you make a runner jump over holes while solving math problems. In Triple Task you drive around obstacles and solve math while remembering what you passed. A session can start at about ten seconds, and Today’s Training is picked for you each day.

Every training except the newest ones is free to play, and the free version shows ads. BrainDojo Plus removes the ads and lets you play the new trainings at any time. Your first session is covered in Getting Started with BrainDojo.