Self-initiating a seated perturbation modifies the neck postural responses in humans

When seated subjects are submitted to a linear acceleration, reports indicate that the kinematic and electromyographic (EMG) responses of the head-neck system can be modulated with the magnitude of the linear acceleration. There is no evidence, however, that head kinematics or neck EMG activity can be modulated when specific knowledge and active control about the onset of platform acceleration are available. Sixteen seated subjects were given forward linear accelerations in two different conditions nested within subjects: reactive and predictive. In the reactive condition, the acceleration was initiated following a variable delay unknown to the subjects whereas in the predictive condition, subjects manually self-initiated the perturbation. All neck muscle activities were decreased 50-100 ms after platform movement onset in the predictive condition relative to the reactive condition, whereas head and neck peak angular positions and velocities were not different between the two conditions. These results suggest that feedforward control could use the self-generated timing information of platform movement onset to scale the appropriate neck motor output.