Multitasking

Multitasking, in the strict sense of the term, is not possible for the human brain when dealing with cognitively demanding tasks. What we call multitasking is, in almost all cases, rapid sequential switching — the brain moving very quickly between tasks rather than processing them in parallel. The subjective experience of multitasking feels like simultaneity, but this experience is an illusion produced by the speed of switching rather than by genuine parallel processing.

The cognitive mechanism at the centre of this is the brain's executive control system — the set of processes responsible for directing attention, inhibiting irrelevant information, and managing the transition between tasks. This system has limited capacity. When it must manage two complex tasks simultaneously, it does so by rapidly alternating between them, and each alternation incurs what researchers call a switch cost: a brief but measurable period of reduced efficiency during which the brain disengages from one task and re-engages with the next.

Switch costs are individually small — typically ranging from 15 to 40 seconds per transition — but their cumulative effect over a working session is significant. A person who switches tasks fifty times across a working day loses somewhere between twelve and thirty minutes to switching alone, before accounting for the reduced quality of output that typically follows each interruption. This calculation does not account for a second effect: cognitive depletion. Switching tasks draws on the executive control system repeatedly, and this depletes its resources over time. By the end of a switching-heavy session, the capacity available for demanding cognitive work is measurably lower than at the start.

The persistence of the multitasking myth is, paradoxically, partly explained by the people who most practise it. Studies consistently find that people who describe themselves as habitual multitaskers perform worse on tests of attention, filtering, and cognitive control than those who do not. If workers were fully aware of the switch cost they incur each time they move between tasks, they would likely structure their time very differently. The myth survives because the inefficiency is invisible from the inside: multitasking creates the subjective sensation of productivity — the feeling of doing a lot — without the corresponding objective output.

None of this suggests that all forms of multitasking are equally costly. Highly automatic tasks — walking, listening to familiar music, simple physical actions — can often be combined with cognitive work with minimal interference. The problem is specific to tasks that both require executive control. When two such tasks are attempted simultaneously, neither receives the full capacity it needs, and both suffer accordingly. The skill worth developing is not multitasking but its alternative: the ability to prioritise, to commit fully to one task, and to resist the pull of the concurrent.