Vigilance

Vigilance is a term with varied definitions, so papers that use the word may not measure the same thing [1]. Most studies of vigilance have used states where sleep and wake are altered, such as drowsiness, sleep deprivation and drugs that act on the central nervous system, but factors from psychophysics to motivation can also affect it [1]. EEG is the most commonly studied physiologic measure of vigilance, and eye movement and autonomic nervous system measures have also been used [1].

One of the leading behavioral tests is the psychomotor vigilance test (PVT), a high signal-load reaction-time test that is very sensitive to sleep deprivation [2]. Four findings recur with it [2]. Sleep deprivation slows responses overall and makes lapses of more than 500 ms and errors of commission more common [2]. It also strengthens the time-on-task effect within each test, and long periods awake reveal interacting circadian and homeostatic sleep drives [2].

On NootropicsWork, vigilance tasks are graded under Attention, not as a separate outcome. When a trial reports vigilance, check three things: whether participants were rested or sleep-deprived, how long the test ran, and which metric was reported.

The metric matters. In a laboratory study of 74 healthy adults aged 22 to 45, tested during 33 hours awake or across 5 nights of 4 hours in bed, PVT measures based on lapses and response speed were more sensitive to sleep loss than mean and median reaction time [3]. The authors concluded that lapse and response-speed metrics should be considered the primary outcomes for the 10-minute PVT, and that mean and median reaction time should not be used as primary measures of alertness [3].

A finding in well-rested people and a finding after a night without sleep answer different questions, and NootropicsWork reports them separately when trials allow it.

Attention, reaction time and mental fatigue.