THE ROLE OF CENTRAL AND PERIPHERAL OPTIC FLOW IN THE CONTROL OF UPRIGHT POSTURE

Several studies have examined the influence of optic flow presented in the central and peripheral fields of view on postural sway, but they have yielded diverging results. Early reports suggested that movement in the periphery was associated with increased sway. Later studies have argued that central movement is equally important. The primary objective of this set of experiments was to further investigate the influence of central and peripheral optic flow on postural equilibrium. The postural sway of 20 healthy subjects (ages 21-30 years) was measured while they viewed moving visual stimuli in a computer-generated immersive environment encompassing their entire horizontal field-of-view (FOV). Two main studies were conducted. In the first, optic flow was presented at different FOVs, but the motion contained only one frequency component during each trial. In the second, the central and peripheral regions of the visual stimulus moved simultaneously but at different frequencies.In the first experiment, the location of the optic flow stimulus significantly affected the number and size of significant postural responses. There were twice as many significant postural responses to the peripheral optic flow condition compared to the central optic flow. In addition, the magnitude of the response to the peripheral optic flow was 6.5 times greater than the response to the central flow. The number and magnitude of significant responses were also greater for higher-frequency stimuli, after accounting for quiet-stance sway components. In the second experiment, there were 3.5 times as many significant postural responses to the peripheral optic flow stimulus as there were to the central optic flow. Likewise, the amount of sway was greater in response to the peripheral stimulus.The results of both experiments suggest that the postural system is more sensitive to anterior-posterior optic flow in the peripheral FOV, regardless of stimulus frequency. These findings have implications for the use of virtual environments, showing that head-mounted displays with a limited central FOV do not provide the visual information most important for postural control. Furthermore, the results suggest that rehabilitation therapists should incorporate peripheral movement cues in treatment to enhance balance retraining