Abstract
When walking, we detect possible collisions with other pedestrians and avoid them, estimating body volumes and safety margins. This safety margin, collision envelope, has been measured in limited conditions: only parallel approaching collisions with lateral offset were tested while subjects watched a walking video. These scenarios limit generalizability for real-world walking where walkers navigate freely with various approaching directions of pedestrians. To evaluate realistic and dynamic collision envelopes in a risk-free environment, we developed a virtual reality walking scenario using the Meta Quest 2 head-mounted display (HMD). While a subject walking with gaze movement in an empty real-world corridor, a corresponding virtual shopping mall with pedestrians approached from 20°, 40°, or 60° bearing angles on a collision course face-to-face or overtaken were shown on HMD. 10 non-colliding pedestrians on various walking paths were also present. Subjects were asked to freely and naturally avoided potential collisions (walking path or speed change). Subjects with homonymous hemianopia (HH; n=6) and subjects with normal vision (NV; n=8) avoided 20 face-to-face and 20 overtaken pedestrians. As a result of the collision avoidance behavior, the trajectories of pedestrians relative to the subjects were changed, and thus the safety margins in various paths were collected. Dynamic collision envelope was calculated as the area kept as the safety margin in more than 50% of trials. HH subjects had larger envelopes (0.95m2, SD=0.60) than NV subjects (0.71m2, SD=0.42; p=0.044) and envelopes were larger when colliders were approaching (1.14m2, SD=0.53) compared to overtaken (0.49, SD=0.19; p<0.001). These results may suggest a more conservative safety margin in HH than NV when avoiding potential collisions. Since the relative walking speeds of the approaching pedestrians were faster than the overtaken pedestrians, estimated time-to-collision may also affect the size and structure of the collision envelope.