The two jobs your brain does one at a time

Multitasking is often listed as a skill in job adverts, and many people believe they are good at it. Answering email during a meeting or texting while driving feels like doing two things at once.

In 2001 the psychologists Joshua Rubinstein, David Meyer and Jeffrey Evans published four experiments in which people either repeated one task or alternated between two, such as sorting shapes by different rules or solving different kinds of sums. Switching always cost time, and the cost grew when the tasks were more complex or less familiar. Each switch might cost only a fraction of a second, but switches add up.

Driving shows what is at stake. In a 2010 University of Utah study, 200 people drove in a simulator while doing a memory and maths task on a hands-free phone. Most braked about 20% more slowly and left 30% more distance to the car ahead. About 1 in 40, whom the researchers called supertaskers, showed no drop. The researchers stressed that the odds of being one are low.

The evidence does not say people can never do two things at once. Walking while talking is easy, because one of the tasks is automatic. The finding is about two tasks that both need attention: the brain mostly takes turns, and each turn costs a little time and accuracy.

The AI angle: AI tools invite multitasking. A chatbot drafts while you sit in a meeting, an agent runs in one tab while you work in another. Checking AI output is itself an attention-heavy task. If you skim a summary or a contract draft while doing something else, you are exactly the person most likely to miss the one confident sentence that is wrong.

The idea behind this caseLesson: Review AI like a manager →

1. 1Do one attention-heavy task at a time, and batch small ones such as email into set slots.
2. 2Give AI output a proper review slot with your full attention, especially numbers, names, dates and anything you will send.
3. 3Be wary of claims that you, or a tool, can do two demanding things at once without cost. Ask how it was measured.
4. 4Never read or write messages, or check AI answers, while driving.