Effects of visual and support surface orientation references upon postural control in vestibular deficient subjects.

Assessment of postural control in vestibular deficient subjects with and without visual and ankle joint sway information permitted: 1) a quantitative assessment of the overall vestibular information used by the individual patient for control of upright posture; 2) an estimate of the extent to which the vestibular deficient subject can appropriately "select" and alternatively use visual and ankle joint somatosensory information for compensatory postural control and 3) quantification of adaptive changes in postural responses to visual and somatosensory inputs. Results from this study support the hypothesis that abnormal vestibular function disrupts the subject's reference to gravity (earth) vertical. This loss of an absolute spatial reference normally provided by vestibular input prevents the resolution of conflicting or inaccurate visual and somatosensory spatial references which may occur during active or passive body movements.