The logic behind sleep deprivation studies is basically sound. The first problem is that sleep is a process that not only occurs in the brain, but is also a process that undoubtedly confers unique benefits to the brain itself. In the parlance familiar to those who are afflicted with a degree in experimental psychology and have thus been subjected to a course in "The Philosophy of Science", the scientific paradigm under which sleep deprivation research is conducted contains some conceptual gaps. The difficulty is as follows: extended continuous wakefulness is an antecedent condition that leads to a predictable, observable outcome: decremented performance. Results from studies conducted to determine the effects of sleep loss on various neurocognitive abilities have proven useful for informing policy, and decision-making in a variety of operational and regulatory environments, and the utilitarian value of such studies for testing work/rest schedules and drug effects remains high.

This chapter presents the methodology, normative data, results from clinical populations and problems associated with the objective measures of sleepiness. The multiple sleep latency test (MSLT) is used in the diagnosis of narcolepsy and the hypersomnias. The maintenance of wakefulness test (MWT) has been used by the FAA and state departments of transportation as a means of screening pilots and commercial drivers for ability to maintain alertness in sedentary work settings. Less research supports the Oxford Sleepiness Resistance (OSLER) and pupillography tests, but the OSLER, which attempts to measure sleep onset without traditional measurement of either performance or EEG, holds promise as a simpler but still time-consuming measure. The tests measure more than a single sleep system and almost certainly reflect the summation of numerous sources of state and trait arousal in addition to the effects of circadian time, prior wakefulness and numerous underlying sleep and arousal pathologies.