Sleep onset facilitation by tones.

In five successive sessions the effect on sleep latencies of three sound stimuli (silence, continuous sound, and an intermittent tone), as well as the combination of a tone plus counting or eye closing, were compared. Tests were conducted under a condition of "artificial insomnia": the subjects attempted sleep in the morning after a full night's sleep. No condition approached the latencies after a night of sleep deprivation. The intermittent tone and the tone plus counting were most effective and showed a differential sessions effect. The tone plus eye opening and closing was counterproductive.