When two decisions are required in quick succession, the second is delayed, because a central stage of processing can handle only one at a time.
Telford reported the effect in 1931 and Welford framed it as a single-channel bottleneck. Perception and motor execution can overlap; the decision stage cannot, so the second response waits. The delay is measurable, involuntary, and unaffected by practice at the component tasks, which is why it constrains genuine multitasking rather than merely discouraging it.
In practice
- An operator asked to judge two alarms arriving together answers the second late, however well trained.
- A driver deciding whether to brake cannot simultaneously decide what to say, and one of them waits.
- Further reading
- Wikipedia
- Subject
- Psychology & Behavior
- Essay
- A century and a half of measuring the mind