Visual field dependence influences balance in patients with stroke

To compare the occurrence of visual field independence/dependence in healthy subjects with patients who are post-stroke using the Rod and Frame Test, and determine whether increased visual dependence is reflected in their postural responses when immersed in a moving visual environment. Eight older and twelve young adults, and twelve patients with cortical or sub-cortical stroke, were asked to align a rod enclosed in a tilted frame to vertical and horizontal. Angular deviations of rod position were calculated and compared. Center-of-mass (COM) of the body was calculated for two patients and two young adults standing in the dark and in an immersive virtual environment to examine their postural responses. Balance of the patients did not appear different from healthy subjects when standing in the dark suggesting they were not dependent on the presence of vision, but more rapid and larger COM displacements emerged in the patients when immersed in a moving visual scene. Patients also exhibited greater errors when aligning the rod compared to both healthy groups. Thus, patients with stroke may be more dependent on visual inputs when they are present, and have more difficulty resolving conflict between the visual and somatosensory cues compared to healthy young or older subjects. This impaired conflict resolution may underlie the rapid instability observed in patients when they were placed in a moving visual environment.