Kathryn Bonnen¹ (), Ziggy Waller; ¹Indiana University

Walking over complex terrains requires that humans gather information about the upcoming path to find good foothold locations. Here we examine the sequences of eye movements used in service of this task, observing how walkers shift their gaze between upcoming footholds. Methods & Data Processing: We recorded the eye movements and body movements of participants (n=8) walking over rough terrain. The data was processed to find fixations and find foothold locations (see Bonnen et al 2021). A photogrammetry technique was applied to reconstruct the depth structure of the ground (Muller et al 2023). Combining the reconstructed ground and the gaze data we calculated the gaze-ground intersections. For each fixation, we found the foothold location closest to the gaze-ground intersection. If the gaze location was less than .4 meters (or about half of a step) from the foothold location, we assigned it to that foothold. We then analyzed these sequences of fixations, focusing on gaze shifts from foothold to foothold (30% of all fixations). Results: We found that when participants shifted their gaze from one foothold to another, it was more likely to be forward down the path (70.4%, .95 CI [67.5, 73.0]), rather than backwards toward their body (7.0%, .95 CI [5.6, 8.7]. The forward gaze shifts were dominated by shifts forward by a single foothold (48.5%, or 69% of all forward shifts). They stayed fixated on the current foothold 22.6% of the time (.95 CI [20.1, 25.2]). Conclusions: When walkers fixate a series of footholds, they tend to move their gaze forward down the path, often shifting forward by a single foothold at a time. This is consistent with the idea that the biomechanics of walking strongly influences the visual search patterns used by human walkers.