Humans typically underestimate travel distance during walking, which can be explained by leaky path integration. The amount of leak, i.e. the underestimation, is determined by the length of the path. Experiments both with blindfolded walking and visually-simulated walking in virtual reality have shown that for movements along curved paths that veer left and right around a central forward direction estimates of the start-to-end distance decrease as the path length increases. Leaky path integration for visual travel distance estimation thus takes place along the actually traversed path even when a straight beeline distance is calculated. We studied whether the same leaky path integration occurs during real self-motion in a full cue situation when visual, vestibular and proprioceptive cues are available together. Twenty subjects walked from a starting point to targets 20, 40 or 60m away, guided by an experimenter. They walked either along a straight line, or along paths that deviated first to the right and then to the left (or vice versa) before they reached the end point. This increased the path length by 10%, 20% or 30%. Subjects then gave a verbal estimate of their beeline distance from the starting point. When compared to results of previous blindfolded and visually-simulated walking experiments, the full-cue estimates showed less dependence on path length, suggesting a smaller leak in path integration in the multisensory condition.

path integration, vision, vestibular, proprioception, motion