This study investigated developmental changes in the use of a contact surfa
ce during the acquisition of upright posture. Standing infants were longitu
dinally examined at four developmental epochs: pulling to stand (PS); stand
ing alone (SA); walking onset (WO); and 1.5 months post-walking (PW). The r
esults revealed that as standing experience increased the force applied to
the contact surface by the hand and the body sway decreased. Applied force
and body sway were consistently related in the anterior-posterior direction
(r approximate to 0.65). Temporally, body sway led applied force (approxim
ate to 45 ms) at the PS, SA, and WO developmental periods. However, at PW,
the temporal relationship reversed and applied force led body sway (approxi
mate to 140 ms). These results indicate that initially infants use surface
contact for mechanical purposes but later for orientation information that
affords prospective control of posture.