OPTIC FLOW-INDUCED SWAY IN ANXIETY DISORDERS ASSOCIATED WITH SPACE AND MOTION DISCOMFORT

This study examined whether anxiety patients with space and motion discomfort (SMD; e.g., fear of heights), like patients with vestibular dysfunction, have increased body sway responses to motion in the visual field. Six patients with panic disorder, agoraphobia, or generalized anxiety disorder, ail with symptoms of SMD, and seven asymptomatic nonanxious control subjects were examined. While standing on a force platform, subjects monocularly viewed optic flow (movement) stimuli projected on a screen in a 60 degrees central visual field. The experiment consisted of (a) a baseline (no-flow) period involving three different visual conditions without flow, (b) an optic flow period involving five different conditions of moving visual stimuli, and (c) a postflow period during which the baseline conditions were repeated. Three of the five optic flow stimuli oscillated at a frequency of 3 cycles/10 s (0.3 Hz) in a manner designed to increase anterior-posterior sway. Postural sway measures were decomposed into powers at four frequency bands, one of which (centered at 0.3 Hz) reflected sway that occurred in tandem with the motion of the oscillating flow stimuli. Results indicated that compared with controls, sway in patients showed (a) greater overall levels; (b) greater flow effects, i.e., greater increases during oscillatory flow conditions compared to baseline; (c) a trend toward greater persistence effects, i.e., greater increases from preflow to postflow periods. Four of the six patients showed sway levels exceeding that of normals by two standard deviations. The results indicate that SMD in patients with anxiety disorders is associated with increased reliance on visual cues for maintaining balance. The situation-specific symptoms of SMD may lead to avoidance behaviors and the development of phobia, such as height phobia or agoraphobia.