FINGERTIP CONTACT INFLUENCES HUMAN POSTURAL CONTROL

Touch and pressure stimulation of the body surface can strongly influe nce apparent body orientation, as well as the maintenance of upright p osture during quiet stance. In the present study, we investigated the relationship between postural sway and contact forces at the fingertip while subjects touched a rigid metal bar. Subjects were tested in the tandem Romberg stance with eyes open or closed under three conditions of fingertip contact: no contact, touch contact (< 0.98 N of force), and force contact (as much force as desired). Touch contact was as eff ective as force contact or sight of the surroundings in reducing postu ral sway when compared to the no contact, eyes closed condition. Body sway and fingertip forces were essentially in phase with force contact , suggesting that fingertip contact forces are physically counteractin g body sway. Time delays between body sway and fingertip forces were m uch larger with light touch contact, suggesting that the fingertip is providing information that allows anticipatory innervation of musculat ure to reduce body sway. The results are related to observations on pr ecision grip as well as the somatosensory, proprioceptive, and motor m echanisms involved in the reduction of body sway.