The volunteers spent 3 nights in a sleep laboratory. The first night was intended to get them used to sleeping in the laboratory, and no studies were done. On the next 2 nights, prerecorded noises from an actual hospital, including human voices, IV alarms, telephones, ice machines, outside traffic, and helicopters, were transmitted into the volunteers' rooms, and the effect of the specific type and volume of noise on their sleep was studied by using an electroencephalogram (EEG). Patient heart rates were monitored with an electrocardiogram (EKG).