Effects of vision on head stability and torques during voluntary pulls made by standing humans

This study tested the hypothesis that vision would improve pitch-plane stabilization of the head by increasing how well neck muscle torque compensates for torques associated with body motion, in a task where standing human subjects made rapid voluntary pulls. Ten subjects performed abrupt horizontal pulls on a handle to two peak force targets, with the eyes open and closed. We evaluated head angular velocity with respect to space. Inverse dynamics were used to subdivide the torque acting on the head into gravito-interactive and muscle components. A torque compensation ratio was computed from those two components. Head angular velocity was lower and the compensation ratio was higher during pulls made with the eyes open, for both force targets. The data suggest that vision enhances head stability by increasing the effectiveness with which muscle torques oppose gravito-interactive torques during voluntary pulls made while standing. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.