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Single-tasking vs. multitasking: what the evidence actually says

"I'm good at multitasking" is one of the most common things people say about how they work. The research is unusually consistent on this one — and it mostly disagrees. Here's what's well-established about doing several things at once versus doing one thing at a time, the one genuine exception, and what it means for how you set up a focus session.

By ComunAI · 29 June 2026 · ~6 min read

Most "multitasking" is really fast switching

Start with what the brain is actually doing. Outside of truly automatic activities (walking while talking), you don't run two demanding tasks in genuine parallel — you flip your attention between them, rapidly. Cognitive psychologists have studied that flip directly for decades: when people alternate between two simple tasks instead of repeating one, they are reliably slower and make more errors on the trials right after a switch. Robert Rogers and Stephen Monsell demonstrated this switch cost in tightly controlled experiments.¹ Evidence: Strong So "multitasking" isn't a separate skill — it's switching, and switching has a price tag.

Where does the price come from? A detailed model by Joshua Rubinstein, David Meyer, and Jeffrey Evans traced it to the mental work of reconfiguring — putting down the rules of one task and loading up the rules of another every time you change.² Evidence: Strong The more the two tasks differ, the bigger the toll. Pay that cost a few hundred times a day and the small frictions add up.

And part of your mind stays behind

Switch costs are measured in milliseconds in the lab; the version that bites in real work unfolds over minutes. Organisational psychologist Sophie Leroy called it attention residue — after you move to a new task, a slice of your attention stays stuck on the previous one, and you perform worse on the new task until that residue clears.³ Evidence: Strong Toggling between a document and a chat thread doesn't give you two streams of progress; it gives you two half-loaded tasks, each dragging on the other. (We unpacked this seam-by-seam cost in Do App Blockers Actually Help You Focus?)

The "supertasker" exception — real, but rare

Here's the fair caveat to a one-sided story. A small line of research has found that a tiny minority of people — around 2.5% in the study that coined the term supertaskers — really can handle two demanding tasks at once with little measurable cost.⁴ Evidence: Moderate It's a genuine finding. But two things follow from it, not one: the effect is real, and it almost certainly doesn't describe you. By definition the overwhelming majority pay the full switching tax — and people are famously poor at judging which group they're in.

The stakes scale with how much the task matters

The clearest real-world demonstration isn't from an office — it's from a car. David Strayer and William Johnston showed that talking on a phone while doing a demanding tracking task degraded performance, including missing more signals, in a way that simply listening to the radio did not.⁵ Evidence: Strong The lesson generalises: the cost of dividing attention is largest exactly when the task is hard and the misses are expensive — which is precisely the deep, careful work a focus session is meant to protect.

Does heavy multitasking at least train the skill?

It's tempting to assume that people who multitask constantly get good at it. The evidence points, if anything, the other way: a well-known study found that people who reported heavy media multitasking were actually worse at filtering out irrelevant information.⁶ But this corner is genuinely unsettled — later studies have produced mixed results, and the direction of cause is unclear. Evidence: Contested We flag it precisely because it's the kind of claim that gets overstated in both directions.

So what should you actually do?

The evidence-based bottom line

For the work that matters, single-tasking isn't a productivity fad — it's the option that fits how attention actually works. Genuine parallel processing of two demanding tasks is rare; for nearly everyone, multitasking is switching, and switching costs time, accuracy, and a trailing residue you can feel. The practical move is unglamorous: pick one thing, make the alternatives harder to reach than the work, and let a bounded session carry you to a real stopping point before you switch. One task at a time, on purpose.