Postural stabilization for the control of touching

We attempted to distinguish between task-related (supra-postural) and perceptual influences on postural motions. Two groups of participants had to make very light tactile contact with an adjacent pliable surface while standing with their eyes closed. In the absence of vision, such light touching with a finger is known to reduce sway. For one group, tactile contact with the surface was merely the result of extending the right forearm. For the other group, variability in the point of tactile contact had to be kept to a minimum. Touching reduced postural sway relative to non-touching only for participants in the latter group. The present results, in combination with others addressing similar task differences, question the assumption that information detected haptically and/or visually is used solely to reduce postural fluctuations. It seems that postural fluctuations are modulated to facilitate performance of tasks over and above the task of standing upright and still.