Long-term alertness tasks require the client’s attention “to be focused continuously for long periods of time on one or more sources of information, in order to detect and respond to small changes in the information presented” (Davies et al. 1984). Vigilance represents a special variant of long-term attention. Vigilance tasks make demands on attention over a long period of time – often a number of hours – and the relevant stimuli typically occur at very irregular intervals and at a very low frequency among a large number of irrelevant stimuli. Vigilance training cannot be effective unless a training session lasts for more than 30 minutes at the minimum.