Definition reprinted with permission from Culebras, Antonio, Clinical Handbook of Sleep Disorders, Butterworth-Heinemann
A series of measurements of the interval from "lights out" to sleep onset that is used in the assessment of the ability to remain awake. Subjects are instructed to try to remain awake in a darkened room while in a semireclined position. Long latencies to sleep are indicative of the ability to remain awake. This test is most useful for assessing the effects of medication on the ability to remain awake.