Effect of truck noises on percentage of deep sleep

Sleep was divided into only two categories, “deep” and “shallow,” the latter including waking, stage 1, and dreaming. For the sake of objectivity and precision the criterion was the level of the alpha frequency and/or the audibility of spindles, from a speeded‐up magnetic tape recording, which was timed by stop watch. Twenty truck noises, at a peak level of 65 dBA, presented every other night, reduced deep sleep of 12, mainly young, subjects by 3%. Adaptation of the waking response occurs despite the separation of noise nights by at least one quiet night. The small adaptation of shifts in sleep level, previously considered insignificant, still persist. Adaptation to sleeping in the laboratory appears to continue for more than the one or two nights usually assumed.