Gaze fixation patterns for negotiating complex ground terrain.

We constantly encounter different ground terrain in our environment that we must safely traverse. The visual system is unique, as it is the only sensory system that can provide accurate and precise information about the environment at a distance through a series of fixations directed to salient objects and/or surfaces. However, how the nervous system utilizes visual information regarding complex ground terrain to guide safe foot placement is not known. We had individuals walk across a walkway with varying ground terrain while gaze fixations were monitored. Several findings emerged. First, gaze fixations were highly task-relevant in that they were predominantly made to areas eventually stepped on and their patterns tended to depend on the task instructions. Second, fixations were frequently directed to a transition region between different surfaces in addition to fixations directed to an actual surface. These results suggest that fixations are directed to regions that maximize the amount of information which the nervous system can integrate in order to facilitate safe foot placement. And third, spatial information of the upcoming ground terrain was sampled sequentially in small sections and continuously updated as the individual traversed the challenging ground terrain. This is suggestive of on-line control and may be beneficial to ensure one is able to adapt to stability concerns, unexpected changes in terrain, or sudden changes in the path taken.