Abstract 302, Date 1:00 PM, Sunday February 22, 2004 (24 hours) Session D4:Vestibular: Clinical
The Role of Central and Peripheral Optic Flow in the Control of Upright Posture Within a Mixed-Frequency Visual Environment
Jeffrey G. Jasko, Patrick J. Sparto, Mark S. Redfern, Patrick J. Loughlin
The goal of this study was to investigate the influence of optic flow on upright posture when patterns in the central and peripheral fields of view (FOVs) move simultaneously but at different sinusoidal frequencies.      Twenty healthy subjects (9 male, 11 female; ages 21-30) participated in the experiment. They were surrounded by an image encompassing 180 x 0 (horiz. x vert.) FOV. The central stimulus was a pattern of alternating black-and-white concentric rings, and the peripheral stimulus consisted of black-and-white checkers. There were two visual combinations: in one, the central optic flow stimulus moved at 0.1 Hz while the peripheral optic flow moved at 0.25 Hz; in the other, the frequencies were reversed. The peak-to-peak amplitude of all stimuli was 16 cm. In addition, there were 2 support surface conditions: fixed and sway-referenced. Head position was recorded during the 90-second trials. A statistical test determined whether there was a significant response at either stimulus frequency. Subjects who had significant responses during of the trials were considered "responders". Root-mean-square (RMS) sway of the responders' data was calculated at both stimulus frequencies using a bandpass filter, and then normalized to their quiet-stance sway. Within each visual/platform condition, the normalized sway at the peripheral frequency was compared to the normalized sway at the central frequency using paired t-tests. There were more significant responses to the peripheral optic flow stimulus (58/80) than there were to the central optic flow (16/80). Thirteen subjects were classified as responders. In 3 of the 4 visual/platform conditions, the normalized RMS sway at the peripheral frequency was significantly greater than the normalized sway at the central frequency. This suggests that the postural system is more sensitive to optic flow in the peripheral FOV, regardless of frequency. Supported by NIH P30-DC05205, K25-AG01049