Both vision and locomotion have been studied separately within controlled lab environments but never together to understand how both are intertwined when a human walks over natural terrain.

Now, the University of Texas at Austin has developed new technologies that track how vision guides foot placement, bringing researchers one step closer to determining what is going on in the brain when a human walks. The development could lead to better treatment for mobility impairments (such as strokes, aging and Parkinson’s) and technology developments such as prosthetics and robots.

"One of the beautiful things about visually guided walking is that it involves every level of our perceptuomotor hierarchy,” says Jonathan Matthis, a postdoctoral researcher in the UT Austin Center for Perceptual Systems. “To really understand it, you need to know how vision works, how planning works, how muscles work, how spines work, how physics work.”

A jury-rigged welding mask and new methods to calibrate the eye tracker with a motion-tracking suit recorded gaze and full-body kinematics. Source: University of TexasResearchers used new motion-capture and eye-tracking technologies to track distinct patterns between the two mechanisms. A jury-rigged welding mask was used to shade the infrared eye cameras from sunlight and new methods were developed to calibrate the eye tracker with a motion-tracking suit to record gaze and full body kinematics as participants navigated three different terrain types including flat, medium and rough.

"Eye movements are incredibly informative as a window into the cognitive process," Matthis says. "By tracking eyes, we get a clear picture of the kind of information the central nervous system needs to complete any given task."

In testing, researchers found people have distinct walking and gaze patterns in each of the terrains. Subjects walked quickly with longer strides on flat terrain, looking down only about half the time. However, over medium and rough terrain, steps became shorter and slower, and participants looked at the ground more than 90 percent of the time to visualize upcoming footholds. Over medium terrain, walkers focused on where their feet would be in two steps while over rough terrain walkers split their gaze between future foot placement in two and three steps to allow for longer-term path planning.

However, a trend emerged in all three terrains where participants consistently looked 1.5 seconds ahead of their current location. This is similar to look-ahead timing seen in research of motor actions (such as stair climbing, driving and reaching) suggesting that this timing plays an important role in human movement.

"The constant look-ahead time suggests that walkers are maintaining some sort of global locomotor strategy that is being tuned to each specific environment," Matthis says. "Walkers use gaze to ensure that they always know what will be coming up 1.5 seconds down the path.”

Researchers believe this knowledge could help to one-day improve clinical treatment of gait-related disorders.

The full research can be found in the journal Current Biology.