Postural stabilization for the control of touching

We attempted to distinguish between task-related (supra-postural) and perce ptual influences on postural motions. Two groups of participants had to mak e very light tactile contact with an adjacent pliable surface while standin g with their eyes closed. In the absence of vision, such light touching wit h 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 othe r group, variability in the point of tactile contact had to be kept to a mi nimum. Touching reduced postural sway relative to non-touching only for par ticipants in the latter group. The present results, in combination with oth ers addressing similar task differences, question the assumption that infor mation detected haptically and/or visually is used solely to reduce postura l fluctuations. It seems that postural fluctuations are modulated to facili tate performance of tasks over and above the task of standing upright and s till. (C) 1999 Elsevier Science B.V. All rights reserved. PsycINFO classifi cation: 2320; 2330; 2346.