Abstract 1241, Date 1:00 pm, Sunday, February 20, 2005 (24 hours) Session : D16: Vestibular: Clinical
Visual Dependence in Postural Control and Spatial Orientation
*Massimo Cenciarini, Patrick J. Loughlin, Mark S. Redfern, Patrick J. Sparto
The purpose of this study was to determine if visual dependence for postural control is related to visual dependence for spatial orientation. Correlations between postural sway responses to sinusoidal moving scenes and reliance on visual cues for spatial orientation were studied. Results from 8 healthy adult subjects are reported here (mean age 2 years, range 22-35 yrs). Sway measurements via center of pressure (COP) were recorded during standing while subjects viewed an antero-posterior optic flow produced by a back-projected virtual reality system that encompassed 180 degrees of the visual field. Subjects stood on either a fixed or sway-referenced support surface during the trials containing visual motion at an amplitude of 16 cm peak-to-peak and constant frequencies of 0.1, 0.25, 0.4, 0., and 1 Hz for 60 seconds. Each test condition was repeated three times, for a total of 30 trials over two sessions. The first session consisted of fixed platform trials, randomized by frequency of the moving scene, and the second session consisted of sway-referenced trials. Subjective visual vertical (SVV) was measured by having subjects seated in the dark align an initially tilted ((40¡) fluorescent rod to vertical. Visual orientation cues were altered by changing the background condition: black (no background), tilted frame (( 28¡), or a rotating dotted pattern (( 30¡/s). Two repetitions of each condition were conducted. Root-mean-square of the COP was used to quantify the amount of postural sway in response to the moving scene visual stimulus. The final angular deviation of the rod from vertical was used as a measure of reliance on visual information. A positive correlation was found between the amount of sway induced by the optic flow and the deviation of the rod from vertical (r=0.5 to 0.88 for the various conditions studied). This result supports the concept of a common mechanism of visual dependence for balance and visual dependence for spatial orientation.