Precision contact of the fingertip reduces postural sway of individuals with bilateral vestibular loss

Contact of the hand with a stationary surface attenuates postural sway in n ormal individuals even when the level of force applied is mechanically inad equate to dampen body motion. We studied whether subjects without vestibula r function would be able to substitute contact cues from the hand for their lost labyrinthine function and be able to balance as well as normal subjec ts in the dark without finger contact. We also studied the relative contrib ution of sight of the test chamber to the two groups. Subjects attempted to maintain a tandem Romberg stance for 25 s under three levels of fingertip contact: no contact; light-touch contact, up to 1 N (approximate to 100 g) force; and unrestricted contact force. Both eyes open and eyes closed condi tions were evaluated. Without contact, none of the vestibular loss subjects could stand for more than a few seconds in the dark without falling; all t he normals could. The vestibular loss subjects were significantly more stab le in the dark with light touch of the index finger than the normal subject s in the dark without touch. They also swayed less in the dark with light t ouch than when permitted sight of the test chamber without touch, and less with sight and touch than just sight. The normal subjects swayed less in th e dark with touch than without, and less with sight and touch than sight al one. These findings show that during quiet stance light touch of the index finger with a stationary surface can be as effective or even more so than v estibular function for minimizing postural sway.