Walking on natural terrain takes precise coordination between vision and body movements to efficiently and stably traverse any given path. But until now, vision and locomotion have been studied separately within controlled lab environments.
To better understand how gaze and gait work together to help us navigate the natural world, UT Austin researchers combined new motion-capture and eye-tracking technologies by jerry-rigging a welding mask around an eye tracker — to shade the infrared eye cameras from sunlight — and calibrating the eye tracker with a motion-tracking suit to record gaze and full-body kinematics as participants navigated through flat, medium and rough terrains.
Researchers found that subjects walked quickly with longer strides on the flat terrain, looking down only about half of the time to briefly scan the upcoming path for obstacles. On the medium and rough terrains, steps became shorter, slower and more variable, with participants looking at the ground more than 90 percent of the time to precisely fixate upcoming footholds. For the medium terrain, focus was directed to where the foot would be in two steps; and for the rough terrain, focus was directed two and three steps ahead.
In all of three terrains, participants consistently looked 1.5 seconds ahead of their current location. This finding is similar to look-ahead timing seen in research on other motor actions — stair climbing, driving and reaching — suggesting that this timing plays an important role in human movement.
“Taking this type of research out of the lab and into the real world allows us to observe human behavior in its natural environment,” says Jonathan Matthis, a postdoctoral researcher in the UT Austin Center for Perceptual Systems. “This gives us more opportunity to discover things we didn’t expect, which will help us advance our scientific knowledge to the benefit of improving clinical treatment of gait-related disorders.”
Feature image: Jonathan Matthis, a postdoctoral researcher in the Center for Perceptual Systems, observes a research participant in “medium terrain” conditions using a motion capture suit, mobile eye tracker and transparent infrared-blocking face shield.