Visual feedback in the lower visual field affects postural control during static standing

Background: The dorsal parietal visual system plays an important role in self-motion perception and spatial cognition. It also strongly responds to visual inputs from the lower visual field. Postural control is modified in a process called sensory reweighting based on the reliability of available sensory sources. The question of whether visual stimuli presented to either the lower or upper visual field affect postural control and sensory reweighting has not been resolved. Research question: Do visual stimuli presented to the lower and upper visual fields affect postural control and sensory reweighting? Methods: Twenty-nine healthy young adults participated in the study. Four conditions (full visual field, upper visual field, lower visual field, and no optic flow condition) were simulated in a VR environment using a headmounted display. The optic flow stimuli used were swarms of small white spheres originating from the central point of the visual field, moving radially towards the periphery, and expanding across the scene. Participants were instructed to stand quietly for 50 s under each visual condition. Using force plate signals, we measured the center of pressure (COP) signal in the horizontal plane and calculated its 95 % ellipse area, root mean square (RMS) deviations, the mean velocity, and power spectral density (PSD). Results: Optic flow in the full and lower visual fields produced significantly smaller 95 % ellipse area and RMS of COP in the anterior-posterior direction compared to optic flow in the upper visual field. Furthermore, the PSD of the lower frequency band (0-0.3 Hz) was decreased and that of higher frequency bands (0.3-1 Hz and 1-3 Hz) was increased for the lower compared to the upper visual field. Significance: Visual feedback affects static postural control more when presented in the lower visual field compared to the upper visual field.