Assessing vestibular contributions during changes in gait trajectory.

Displacing prisms and galvanic stimulation were used to examine visual-vestibular interactions during target-directed gait. Participants walked towards a wall 6 m away. After taking four steps, a target on the wall, located directly in front or to the right of the participant, was illuminated. Participants continued walking towards the target. Galvanic vestibular stimulation was triggered at either gait initiation, a step before the potential turn, or at target illumination. Although the visual and vestibular perturbations significantly altered gait trajectory, the greatest interaction occurred when galvanic stimulation was triggered one step before the target appeared. This implies an increase in the weighting of vestibular inputs just before turning to prepare for the potential change in direction.