Changes to walking trajectories to avoid altitude-related threats

Walking in complex environments demands changes in locomotor behavior. Despite knowledge of how altitude threats, such as walking at high heights, affect spatiotemporal measures of gait, it is unclear how individuals select walking trajectories when there are altitude threats. The purpose of this study was to use determine how individuals modify their walking trajectory in the presence of altitude threats (i.e., a cliff edge). We hypothesized that individuals would change their trajectory by walking away from the threat, thereby increasing their lateral deviation orthogonal to the task goals, when walking at high heights. We tested this hypothesis by placing participants (n=6) in a virtual reality environment and giving the task of walking along the length of a rectangular plank at low (ground level) and high (15 meters) height conditions. The lateral deviation was quantified as the displacement along the width of the plank. People modified their walking trajectories by increasing lateral deviation when walking at high versus low heights [mean (SD) difference = 2.7 (2.2) in; p = 0.027]. All participants reported that more mental effort was necessary to complete the walking tasks at high height [mean (SD) difference = 19.9 (14.1) data points; p=0.006]. These results suggest that locomotor behavior considers environmental threats to be relevant to task goals in a risk minimization framework, and support the idea that individuals select path trajectories that accommodate their risk tolerance.