this invention includes a plurality of ambient sensors at least one human subject stimulator , at least one sensor adapted to detect the human subject response to the stimuli , and a controller programmed to receive information from the environmental or ambient sensors , to control the stimulators , and to record the human subject &# 39 ; s response to the stimuli via the human response sensors . the invention can monitor and record , over a series of consecutive time periods , the human subject &# 39 ; s vigilance , level of physical activity , and other physiological , physical , and chemical variables pertaining to the subject and his or her ambient environment . the invention can be used to prevent impairments in mental performance occurring due to fatigue or exposure to adverse environmental conditions or human subject condition . based on continuous evaluations of the status of the subject the vigilance monitor can be programmed to automatically intervene to prevent degradation in mental performance by providing a warning to the subject or to others .