Vigilance and Mental Workload at Work: Why Attention Drops, and How to Measure It

What is vigilance?

Vigilance is the ability to keep attention on a task over a long period, often to detect an event that rarely happens: an alarm in a control room, a change on a screen, a hazard on the road.

Its best-known feature is the vigilance decrement: detection performance declines with time on task, sometimes within the first tens of minutes.

Hard mental work, not boredom

One could think that monitoring a calm process asks little of the brain. Research says the opposite: a review of vigilance studies shows that sustained attention is demanding mental work, with high workload and stress reported by the people doing it ^[1].

Attention is not stable either. In a sustained attention task, performance fluctuates from moment to moment between periods in the zone, stable and accurate, and periods out of the zone, more variable and error prone ^[3].

What EEG adds

A review of neurophysiological measures in aircraft pilots and car drivers describes how EEG, together with other signals, has been used to assess mental workload, fatigue and drowsiness ^[2].

The value of EEG is to follow these states during the task, continuously, rather than reconstructing them after an incident.

What a measurement is for

• Understanding: seeing at which moments of a shift or a scenario load concentrates and vigilance drops.
• Training: letting each person see their own state during a scenario and learn to manage it.
• Organisation: informing breaks, rotations and workstation design with a measurement of the human state.

Limits

• Findings come mostly from laboratory tasks and simulators; transfer to each workplace has to be checked.
• Each person has their own baseline, and a single marker is not enough to conclude.
• A measurement of vigilance does not replace safety rules or the judgement of the people in charge.