Optical flow, spatial orientation, and the control of posture in the elderly.

Stabliographic techniques were used to better understand the role of the visual system in the perceptual motor activity of older people as it relates to the maintenance of postural control. The central research question was to determine the sensitivity of the subject's visual system to changes in three standard conditions of optical flow generated by an experimental moving room. Any movement that was present as a function of this optical flow field was recorded on a force platform and expressed in movement of a computed center-of-pressure variable. Movement of the center of pressure was recorded in a baseline condition and in the experimental conditions, and the data were analyzed with respect to differences in the three conditions of optical flow and between both younger and older subjects. The older subject group exhibited less stability than the younger subjects in response to the baseline conditions; and, after adjusting for baseline movement, the center-of-pressure motions of younger and older subjects, in response to the experimental conditions, were compared. No reliable differences were present between younger and older subjects for the radial optical flow condition; in the lamellar flow condition, older subjects moved significantly more than younger subjects; and, in the combined condition (global), the movement of the older subjects was significantly greater than that of the younger subjects for all motion variables recorded. The results are interpreted and discussed both in terms of their implication for falling in the elderly and in the context of an ecological interpretation of the role of vision in maintaining postural stability while both stationary and in motion.