Certain practical measures to counteract sleepiness under monotonous driving conditions, have been evaluated. Three treatments were given separately during a 30 min rest period between two, one-hour monotonous drives: a placebo (decaffeinated coffee), a nap (less than 15 minutes), and 150 mg caffeine (in decaffeinated coffee). Ten subjects (experienced drivers) underwent all conditions in a balanced design. Sleep was restricted to 5 hours the night before each treatment condition. An interactive and instrumented driving simulator emulated monotonous driving. Subjects drove between 14:00h and 16:30h. Major and minor lane deviations were identified. Subjects reported their subjective alert/sleepiness levels, and recordings were made of brain (electroencephalogram - EEG) and eye activites (electro-oculograms - EOGs). Video records showed facial/postural changes. Both caffeine and a nap significantly reduced driving impairments, subjective sleepiness, and EEG activities indicative of drowsiness; these effects lasted for the 1 hour duration of driving after treatment. The findings with caffeine were consistent across subjects, whereas those for nap were less so, depending on the ability to nap (most subjects napped). Eye movements (e.g. eye rolling) were unreliable in determining sleepiness and inferior to the other measures. Changes in driving performance and EEG were closely linked, but there was a small time lag between the two. Subjects were aware of their deteriorating EEG state of alertness almost "on line". Self-knowledge is a good guide to real sleepiness, but subjects may not realise that sleepiness portends sleep, which may descend rapidly thereafter. If one has to drive whilst sleepy, then a break with coffee or a nap can be beneficial, but for only a while. (A)
Abstract