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Why Multitasking Is a Lie Your Brain Tells You

By Sofia Brennan|Focus & Attention•April 17, 2026•7 min read•37,646 views
Why Multitasking Is a Lie Your Brain Tells You

The Multitasking Myth

The word multitasking entered common usage from computing, where it describes the capacity to execute multiple processes simultaneously. Applied to human cognition, it carries the implication that the brain can genuinely attend to multiple tasks at the same time — processing information from multiple streams in parallel without cost to any stream. This implication is, with very limited exceptions, false.

What humans do when they appear to multitask is task-switch — rapidly alternating attention between different tasks rather than genuinely attending to them simultaneously. The switching may be rapid enough to create the subjective impression of simultaneity, but the neural processes of attention and working memory are largely serial, not parallel. Each switch carries costs that accumulate across a session.

The Cost of Task-Switching

Research on task-switching has documented several distinct costs. The first is the switch cost itself — a performance decrement that occurs immediately after switching to a new task, even when both tasks are well-practised. Response time slows and error rates increase for a brief period after each switch, as the brain reconfigures working memory to support the new task.

The second cost is attention residue, identified by Sophie Leroy: when attention is switched away from an unfinished task, cognitive resources continue to be partially allocated to that task, reducing capacity for the new one. This residue persists until the previous task reaches a point of psychological completion, which may not occur until it is actually finished.

Key Finding

Research by David Meyer at the University of Michigan found that task-switching can reduce productivity by as much as 40%, even when the switches are brief and the tasks are familiar. The cost accumulates over a day of interrupted work.

Media Multitasking and Cognitive Control

Heavy media multitasking — the simultaneous use of multiple media streams, such as watching television while using a smartphone — has attracted particular research attention. Eyal Ophir, Clifford Nass, and Anthony Wagner at Stanford published an influential 2009 study comparing heavy and light media multitaskers on various cognitive measures. Counterintuitively, heavy media multitaskers performed worse than light multitaskers on tests of attentional filtering, working memory, and task-switching ability.

The researchers proposed that heavy media multitaskers were less able to filter irrelevant information — they were more distracted by irrelevant stimuli, not less. Habitual media multitasking appeared to have trained a mode of broad, inclusive attention that was disadvantageous when focused attention was required.

The Supertasker Exception

A small proportion of people — estimated at around 2% — appear to show little or no performance cost from simultaneous task demands. These individuals, dubbed supertaskers by researchers Jason Watson and David Strayer, can genuinely perform two demanding tasks simultaneously without the performance decrements observed in most people.

The existence of supertaskers is scientifically interesting but practically limited in its implications. The vast majority of people are not supertaskers, and most people who believe they are multitasking effectively are not. Research consistently finds that self-assessments of multitasking ability are poorly calibrated — people with the worst multitasking performance tend to overestimate their ability the most.

What Genuine Parallel Processing Looks Like

The brain does perform some processes in parallel. Automatic, well-practised behaviours — walking, breathing, maintaining balance — can occur simultaneously with conscious thought because they do not compete for working memory or attentional control. This is why experienced drivers can hold a conversation while driving on a familiar route, while novice drivers cannot. The driving task, once automatised, no longer requires conscious attentional resources.

The practical implication is that two demanding tasks that both require attentional control cannot be done simultaneously without cost to at least one. Two tasks where one is fully automatised can often be combined without meaningful cost. The distinction between automatised and controlled processing is therefore central to understanding when apparent multitasking is genuinely possible and when it is an expensive illusion.

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