The British Royal Air Force had a problem. It was 1943, and the Brits were using radar material to spot German submarines sneaking around off the western coast of France. The young man sitting in planes circling over the Bay of Biscay had more than enough motivation to keep a watchful eye for the telltale blips on the screens in front of them. Yet they had a concern predisposition to miss the signals they’d been trained to recognize. The longer they wasted looking at the screen, the less reliable they became.
The RAF could tell their skills degraded over duration, but it wasn’t sure how long “its been” safe to keep them at their vital chore. So they brought in Norman Mackworth. Mackworth brought in his clock.
The British psychologist introduced RAF cadets alone in a sparse and silent wooden cabin where they are able to sit 7 paws from a clock 10 inches in diameter. The clock had a single side. Every second, the side moved forward a one-third of an inch. But at random interludes, it moved twice that interval. The subject’s task was to watch the clock, and press a morse key( that occasion telegraph operators use) each time it made the double rush. Some of the cadets sat there for 30 hours, others an hour, the unluckiest two hours. Mackworth worked in all sorts of variables–some themes get phone calls during the test, others got amphetamines–but the clear takeaway was it took less than half an hour for their attention to wander.
In Breakdown of Vigilance During Prolonged Visual Search, Mackworth retraced an acknowledgement of this phenomenon back to Shakespeare’s The Tempest 😛 TAGEND
For now they are oppress’d with movement, they Will not , nor cannot, use such vigilance As when they are fresh.
Before and since Mackworth’s time, the “vigilance decrement” has caused trouble everywhere humans are kindly requested to spend long periods of primarily uneventful duration, watching for easy to discern but impossible to predict signals. Security lookouts suffer from it. So do the person or persons looking after nuclear reactor and Predator monotones. Same starts for TSA agents and lifeguards.