Gaze and the Control of Foot Placement When Walking in Natural Terrain

Abstract

Human locomotion through natural environments requires precise coordination between the biomechanics of the bipedal gait cycle and the eye movements that gather the information needed to guide foot placement. However, little is known about how the visual and locomotor systems work together to support movement through the world. We developed a system to simultaneously record gaze and full-body kinematics during locomotion over different outdoor terrains. We found that not only do walkers tune their gaze behavior to the specific information needed to traverse paths of varying complexity but that they do so while maintaining a constant temporal look-ahead window across all terrains. This strategy allows walkers to use gaze to tailor their energetically optimal preferred gait cycle to the upcoming path in order to balance between the drive to move efficiently and the need to place the feet in stable locations. Eye movements and locomotion are intimately linked in a way that reflects the integration of energetic costs, environmental uncertainty, and momentary informational demands of the locomotor task. Thus, the relationship between gaze and gait reveals the structure of the sensorimotor decisions that support successful performance in the face of the varying demands of the natural world. In Brief Matthis et al. recorded subjects' gaze and full-body kinematics during real-world locomotion. Walkers show distinct gaze strategies appropriate for the demands of each terrain. Nevertheless, walkers also adopted a constant look-ahead time across all terrains. Walkers tune gaze behavior to sustain consistent locomotor strategy in all terrains.

Downward Gazing for Steadiness

“…That being said, in this experiment we did not try to investigate a specific mechanism(s), but to establish the overall effect of DWG to commonly reported distances (Patla and Vickers, 2003;Marigold and Patla, 2007;Matthis, Yates and Hayhoe, 2018) during walking. Results of this experiment were unambiguous, demonstrating that DWG to one and three meters ahead (roughly corresponding to 1-1.5 and 3-4 steps ahead, respectively) significantly increased postural steadiness.…”

“…Visual information is important for guiding human locomotion (Patla, 1997;Marigold, 2008). When walking on uneven surface (Marigold and Patla, 2007) or complex terrain (Matthis, Yates and Hayhoe, 2018), healthy individuals tend to gaze downward, presumably to reduce the surface's uncertainty (Domínguez-Zamora, Gunn and Marigold, 2018) by identifying individual footholds and use this information, in feedforward (Matthis, Barton and Fajen, 2015) and/or online (Reynolds and Day, 2005a;Reynolds and Day, 2005b;Smid and Den Otter, 2013), to control the leg's trajectory. Given a well-established relation between gaze behavior and footholds in precise stepping paradigms (e.g.…”

Sequential Decision Fusion for Environmental Classification in Assistive Walking

“…Another method to predict the motion intent of amputees is to recognize the signals in the prosthesis-environment loop [17]. Visual information can guide able-bodied people to change locomotion modes in different environments [18]. Similarly, environmental recognition can provide the prosthesis with the environmental context of the human motion intent and help the prosthesis to reconstruct the vision-locomotion loop.…”