Vigilance, alertness, or sustained attention: physiological basis and measurement

Abstract

Vigilance is a term with varied definitions but the most common usage is sustained attention or tonic alertness. This usage of vigilance implies both the degree of arousal on the sleep-wake axis and the level of cognitive performance. There are many interacting neural and neurotransmitter systems that affect vigilance. Most studies of vigilance have relied on states where the sleep-wake state is altered, e.g. drowsiness, sleep-deprivation, and CNS-active drugs, but there are factors ranging from psychophysics to motivation that may impact vigilance. While EEG is the most commonly studied physiologic measure of vigilance, various measures of eye movement and of autonomic nervous system activity have also been used. This review paper discusses the underlying neural basis of vigilance and its assessment using physiologic tools. Since, assessment of vigilance requires assessment of cognitive function this aspect is also discussed.

Fig. 1

Error rate and EEG spectral power for a single subject during a 28-min continuous performance task. The local error rate is plotted to the left of the spectra. Note the relationship between changes in the EEG spectrum (decreases in alpha frequency and increases in theta frequency activity) and increasing error rate over time. From Makeig et al. (1993).