Spontaneous behavioral coordination between avoiding pedestrians requires mutual anticipation rather than mutual gaze

Pedestrians threading through a crowd is a striking example of coordinated actions. Mutual anticipation between pedestrians is a candidate mechanism underlying such coordination. To examine this possibility, we experimentally intervened pairs of pedestrians performing simple avoidance tasks. Pedestrians in the baseline condition spontaneously coordinated their walking speed and angle until passing one another. Visually distracting one of the pedestrians decreased the level of behavioral coordination. Importantly, blocking the pedestrians' gaze information alone did not alter their walking. These results indicate that spontaneous coordination requires mutual anticipation. Eye movement analysis showed that the direction of a pedestrian's gaze changed depending on the uncertainty of the oncoming pedestrian's motion, and that pedestrians tended to look ahead toward the ultimate passing direction before they actually walked in that direction. We propose that body motion cues may be sufficient and available for implicit negotiation of potential future motions.