Where do people look when they walk or run at different speeds?

When walking or running, people spend part of their time looking at the ground surface in front of them. They presumably do so to guide their future foot placement. We were interested in how far ahead they look when they do so. This distance probably depends on the time it takes to select and guide the foot to suitable positions. If this time is independent of how people walk or run, how far ahead they look will be proportional to their movement speed. But considering the fundamental role of ground reaction forces in walking and running, the time needed to guide the foot may primarily depend on the step frequency, with people looking a certain number of steps ahead. If so, how far ahead they look will be proportional to their step length. To examine to what extent speed and step length determine where people look, we asked twelve participants to walk at three different speeds, as well as to run at three different speeds. We measured their eye movements, head orientation, speed, and step frequency. We combined their gaze elevation with their eye height to estimate how far away they were looking. Our participants did not scale how far away they looked to their speed of locomotion: they reached where they were looking earlier when they were moving faster. Neither did they scale how far away they looked to their step length: they looked fewer steps ahead when moving faster. The participants appeared to look a certain distance ahead, irrespective of their speed and step length, both when running and when walking. They did look less far ahead when running than when walking.