Stephanie M Shields¹ (), Kathryn Bonnen¹; ¹Indiana University

During visually-guided walking, a person’s view of the environment changes with their body, head, and eye movements. What they see then influences their subsequent movements, forming a sensorimotor control loop. A crucial piece of that loop is the precise coordination between the body, head, and eyes in controlling gaze location. Here, we aimed to study such coordination in unconstrained locomotion, with an initial focus on coordination between the eyes and head. We used previously published data from a study that simultaneously recorded participants’ eye and body movements while they walked along a nature trail with varying terrain complexity (Bonnen et al., 2021). Analyzing changes in eye and head direction (azimuth and elevation), we found that the eyes moved more frequently and in a wider variety of directions than the head. The distribution of eye movement directions was fairly even (with a slight cardinal bias) while changes in head direction were more vertical than horizontal. As a result, horizontal gaze shifts were most common. Analyzing the timing of these changes suggests, in line with existing literature, that the temporal relationship between eye and head movements is flexible, with gaze shifts most often preceding or co-occurring with head movements. Additionally, we compared results across terrain complexity and found variation in the direction and timing of changes. Differences in the distributions of change directions are consistent with previous findings suggesting that terrain complexity impacts gaze behavior, seemingly by increasing task difficulty and forcing participants to pay more attention to the ground ahead of them. Future work will aim to test that connection by analyzing eye-head coordination conditioned on the current eye and head directions relative to the walking path. These results will help advance understanding of how eye and movements synergistically interact during natural behavior.