Postural stability and stereo-ambiguity in man-designed visual environments

Measuring postural stability in the presence of a stereoambiguous stimulus is discussed. The existence of the following elements of the theoretical chain of events which leads to disorientation is shown for the first time: (a) inappropriate binocular convergence consistent with false fusion, and the wallpaper illusion, (b) heightened postural instability, and (c) correlation between subjective disorientation and postural instability. The modern rectilinear visual environment contains visual stimuli for which evolution has not had time to optimally shape visual processing. One such stimulus, periodic stripes, is known to lead to visual depth ambiguity. The authors show that postural instability, as measured by the variance of fore and aft sway, is increased by viewing such stimuli. This instability may be the precursor of falls. Designers must evaluate the visual impressions conveyed by their systems in order to avoid postural instability due to visual ambiguity.