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 stab ilization of the head by increasing how well neck muscle torque compensates for torques associated with body motion, in a task where standing human su bjects 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 dynamic s were used to subdivide the torque acting on the head into gravito-interac tive and muscle components. A torque compensation ratio was computed from t hose two components. Head angular velocity was lower and the compensation r atio was higher during pulls made with the eyes open, for both force target s. The data suggest that vision enhances head stability by increasing the e ffectiveness with which muscle torques oppose gravito-interactive torques d uring voluntary pulls made while standing. (C) 2000 Elsevier Science Irelan d Ltd. All rights reserved.