Mutual avoidance behaviours of two pedestrians passing through an aperture

Humans use visual information to safely guide locomotion to avoid collisions with objects or other people within cluttered environments. The purpose of the current study was to examine head-on mutual avoidance behaviours of two young adults when approaching an aperture from opposite sides. It was hypothesized that when two young adults are on a collision course, both pedestrians would accurately perceive the difference in arrival time between one another to predict and maintain passing order through an aperture. Nineteen young adults ($\overline{x}=21.35\pm 0.49$ years, 9 males and 10 females) participated in the study and interacted with a female research assistant (RA) (22 years, 157.5 cm). Starting at one of two locations on opposite sides of a 10 m pathway, the participant and the RA were instructed to approach one another, and mutually decide who would pass first through an aperture located halfway (5 m) along the path. Kinematic trunk data was collected from both the participant and the RA using the Optotrak motion analysis system. The results revealed that the walkers were able to accurately perceive and maintain the predicted order of crossing (i.e., predicted order matched their observed crossing order) on 90.9 % of the trials. This finding indicate that individuals are in-tune to the visual information necessary in determining and maintaining crossing order, such that the walker passing second (P2) slowed down and deviated from the path to allow the other walker (P1) to pass through the doorway first. Additionally, it was revealed that individuals distribute their gaze fixations equally between the aperture and the approaching person prior to crossing the aperture. The results suggest that when two young adults are approaching a doorway from opposite sides, they may rely on the coupling of two optical expansion rates, or tau-coupling, to determine crossing order as indicated by the low number of inversions. While gaze behaviours are coupled with locomotion to maintaining path trajectory and determining crossing order.