Adaptation of modern biomedical technology to the study of sleep in the natural environment was reported. A small portable unit, containing two electroencephalographs (EEG), one electrooculograph (EOG), one electrocardiograph preamplifier, and a fifth channel as an indicator of signalled awakening, was constructed. A sixth channel was connected to a sound level meter to encode environmental noise. Each channel was allocated to a particular time slot, with one unique time slot for synchronization purposes. If only one subject was recorded, the multiplexed signal was transmitted over the British medical band via a single stage frequency modulated transmitter. When two or more subjects were recorded simultaneously, cable telemetry was adopted. For 8 hour sleep monitoring, silver/silver-chloride electrodes were attached to subjects, and EOG electrodes were placed on outer canthi of each eye. Computer analysis of sleep opened not only the feasibility of learning details hidden in data, but also improved objectivity of interpretation. At the time this paper was prepared, four hardware circuits had been constructed, alpha, spindle, and delta detectors for EEG, and a rapid eye movement detector for EOG. Software was designed to imitate human scoring procedures. Some changes were introduced into the logic. Two frequently used tests, four choice serial reaction time (4CH) and unprepared simple reaction time (USRT), were completely redesigned. Two other tests, short term memory and Wilkinson vigilance test, were modified for field situation. USRT and 4CH were housed in portable cassette recorders. Field recordings were replayed, decoded, and analyzed by digital computer. Computer sleep profile was augmented with two questionnaires, Stanford sleepiness scale and a locally designed scale, in which subjects assessed their patterns and quality of sleep.
The Twenty-Four Hour Workday: Proceedings of a Symposium on Variations in Work-Sleep Schedules, Division of Biomedical and Behavioral Science, NIOSH, U.S. Department of Health and Human Services, Cincinnati, Ohio, DHHS (NIOSH) Publication No. 81-127