Mix it Up; or, How to Beat Vigilance Decrement

In the mid-1940s, the British psychologist Norman Mackworth set about to investigate why, during World War II, the Royal Air Force’s radar and sonar operators would miss weak signals that could suggest submerged enemy vessels.

Mackworth was particularly interested in why this observed phenomenon was likely to happen more towards the end of the operators’ shifts.

The “Mackworth Clock” study established that after 30 minutes in an intense task, there was a deterioration of 10–15% in the accuracy of signal detection. Fatigue ensued, and blood flow to the brain decreased. This deterioration continued as the time on task increased. Mackworth also found that short breaks restored performance.

The Way Attention Works

Research on “vigilance” (that’s psychology-speak for attention) has demonstrated that attention is a limited resource. Most of us find it challenging to sustain constant attention to a single task for long periods, especially if the task were demanding, tedious, and boring. Students, for example, can’t concentrate and follow lectures for more a few minutes at a time. This notion of limited and waning attention is called “vigilance decrement.”

Sustained Vigilance Requires Hard Mental Work

Vigilance decrement also increases error rates and slows down reaction times, especially in tasks that need sustained attention—security personnel, surveillance-camera monitors, pilots and vehicle drivers, medical diagnostic screeners, students, and so on—even engineers who train self-driving cars.

As with Mackworth’s study, vigilance decrement is most pronounced when monitoring screens and displays, often over periods as short as 10 or 15 minutes.

TSA screeners in America, for instance, continually rotate positions throughout their shift to avoid making mistakes and missing details—especially small but important details. They even rotate among different stations. Every TSA officer is trained in all the tasks on the floor, including x-ray screening, searching bags, validating tickets and passports, and conducting pat-down searches. TSA agents take frequent breaks, sometimes resting for 30 minutes every two or three hours.

Idea for Impact: To Beat Vigilance Decrement, Take Truly Restful Breaks

• Rest well before undertaking a task that requires sustained attention. The airline industry has specific guidelines for duty, rest, and sleep requirements to combat the risks of fatigue in aircrews.
• Hand over surveillance tasks as frequently as possible.
• Mix ’em up. Try interleaving—instead of focusing on a single task, frequently switch between different ones.

During the current COVID-19 lockdown, you’ll work better with breaks. Mix up how you sequence your work. Avoid doing the same tasks in the same order each day.