The sensory organs of balance permit a person to maintain upright posture and to position objects in the central field of vision where image clarity is best. Physicians have long used stance and gait as pointers to damage and disease; likewise drugs and alcohol will produce balance disturbances in otherwise healthy individuals. Changes in steadiness have thus served in both clinical and research settings as an overall index of central nervous system functioning. Although some clinical batteries exist, these tend to be expensive and require cumbersome, fixed apparatuses. There has not been a portable, automatically scored, and affordable way to measure postural stability in experimental work. In Phase I of this effort, we hypothesized that measures of head position alone could adequately represent overall steadiness, designed and built a prototype device using new video recording and image capturing technology, and developed software for automated analysis of head movements from video records. Sixteen postural measures were evaluated, and one was selected for further use based on measurement properties. Using the prototype, we analyzed head movements and obtained three key results: a) Head movements for a single subject showed perfect agreement with group results on a less sophisticated "time to fall" measure, showing that the approach was useful for individual measurement; b) more and larger head movements were found with increasing doses of alcohol; and c) two aviators showed significant decreases in postural steadiness after using a flight simulator. POTENTIAL COMMERCIAL APPLICATIONS OF THE RESEARCH A general measure of central nervous function which can be connected to performance in everyday life could be used, a) as a fitness-for-duty index in the workplace; b) to measure aftereffects which are increasingly being reported in connection with the newly developing virtual reality systems; c) to index time-course change of disease, drug therapy, or drug usage; and d) to assess postura l stability in the elderly, infirm, or other clinical populations.
