Award Lecture: 2022 Tillyer Award Lecture: Visual Control of Locomotion in Natural Environments.

Control of locomotion is clearly an important role for vision, but one that we know little about. Considerable attention has been devoted to the potential role of retinal motion patterns, generated by self-motion, in steering towards a goal. These motion patterns are determined by an interconnected set of factors, including gaze location, gaze stabilization, the structure of the environment, and the walker's behavioral goals. We have collected measurements of the eyes, the body, and the 3D environment during locomotion in natural terrains. This has allowed us to explore the resulting retinal motion patterns, and how they might be used to guide behavior. Large variations in head direction during the gait cycle make it problematic for use in steering towards a goal, but gaze stabilization leads to regularities in the retinal motion patterns that could provide a postural control signal during locomotion. Another aspect of the visual control of locomotion is the choice of foot placement in rugged terrain. We examined the role of local height changes in the terrain, and showed that visual selection of footholds reflects a complex interplay between energetic costs and the need for stable foot placement. Thus visual signals about motion and depth act as time-varying local control signals for the momentary disposition of the body rather than steering toward more distant goals.