Aging Clin Exp Res, Vol. 19, No. 6 438 Key words: Aging, posture, stability, virtual reality, vision. Correspondence: Pamela S. Haibach, PhD, Department of Physical Education, SUNY Brockport, B310 Tuttle North, Brockport, NY 14420, USA E-mail: phaibach@brockport.edu Received June 30, 2006; accepted in revised form November 6, 2006. INTRODUCTION The amount of time that the body is in an unstable po- sition increases the likelihood of a potential fall. Tempo- ral limitations in the maintenance of postural control have been found to be an important indicator of postural stability in standing (1, 2) and stepping tasks (3) as a function of age. Spatial-temporal components are fun- damental to the maintenance of postural control (4). A physical perturbation or volitional movement is not the only means of perturbing the postural state in upright standing. Dynamic visual environments can also induce strong postural responses. For example, Lee’s (5) moving room paradigm created an illusory effect due to percep- tual information contrasting a perceived environment vs the real environment. The participant perceived the mo- tion of his/her body in vertical space and in turn oscillated with the moving room. Transient perceptual conflicts then arise between the visual information and the orien- tation of the environment (6). These studies have revealed the fundamental role of vi- sual perception as a source of postural reorganization. Older adults have been reported to rely on their visual in- puts more for postural stability than younger individuals due to other sensory losses (7) which may explain the en- hanced postural sway found in elderly adults during dy- namic visual environments (8). Although many investigations have examined the effect of a dynamic visual environment on postural sway (1, 8- 11), time dependence of the visual system to recalibrate and sustain postural stability following a visual perturbation, has not been examined. In this investigation, temporal lim- itations to postural control were assessed following a solely visual perturbation using virtual reality without any physical perturbations or changes in postural orienta- tion other than that induced from the visual motion. Vir- tual reality allows a flexible method of generating a vari- ety of visual stimuli (12-14). The role of age upon postural control was of particu- lar interest with significant temporal lags in the ability to reacquire postural stability expected with old adults (8 th decade) in comparison to young adults (late 2 nd decade) Aging Clinical and Experimental Research Aging and time-to-postural stability following a visual perturbation Pamela S. Haibach, Semyon M. Slobounov, Elena S. Slobounova, and Karl M. Newell Department of Kinesiology, The Pennsylvania State University, University Park, PA, USA ABSTRACT. Background and aims: Postural stability is essential to the performance of most daily activities and is necessary to lead an independent lifestyle. Most functional assessments of balance have only evaluated spatial properties of posture, however, assessments should also evaluate balance in the temporal domain. Both domains provide crucial information to an indi- vidual’s postural stability. The following study examines time to regain stability and the magnitude of postural motion following a virtual perturbation. Methods: To ex- amine the temporal limitations imposed by age (n=45), 3 adult age groups were tested, young (18-19 yr), young old (60-69 yr), and old adults (70-79 yr). Participants were placed into a virtual room appearing as if the visual surround moved in a discrete antero-posterior motion. A force platform was used to assess postural motion across 4 visual perturbation conditions, 9 and 18 cm and 0.3 and 0.6 Hz. Results: Young adults exhibited sig- nificantly less postural motion than both of the older age groups and required the least amount of time to regain postural stability following the discrete visual pertur- bation, while the old adults required the greatest amount of time. Conclusions: These findings indicate that even small visual perturbations induce strong temporal limitations which are magnified by advancing age. Fur- thermore, the postural saturation (reduction in postural motion) that is typically found in young adults with in- creasing movement magnitude was not found in either of the older adult groups. Older adults are at a higher risk of losing balance during this period of time to reacquire postural stability which appears to be unaf- fected by elevated visual motion. (Aging Clin Exp Res 2007; 19: 438-443) © 2007, Editrice Kurtis