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Gregory Dachner, William Warren; Visual information for the joint control of speed and direction in pedestrian following. Journal of Vision 2016;16(12):769. doi: 10.1167/16.12.769.
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© 2017 Association for Research in Vision and Ophthalmology.
During collective crowd motion, an individual pedestrian coordinates their locomotion with visible neighbors. Previously, we found that an individual matches the walking speed (Rio et. al. 2014) and heading direction (Dachner & Warren 2015) of a neighbor. Here we investigate the visual information that jointly governs speed and heading. We hypothesize that when the neighbor is in front, optical expansion controls speed while change in bearing controls heading direction; but when the neighbor is to one side, these relations reverse. In Experiment 1, participants followed a virtual pole (40cm) that changed speed or direction or both, while the walking trajectory was recorded. We varied the target's direction change (left, no change, right), speed change (decrease, no change, increase), initial position (0° in front, 30° or 60° to the side), and initial distance (1m, 4m). Results show that the follower matched the target's final direction (F(2,33)=2806.53, p< 0.001) and final speed (F(2,33)=128.27, p< 0.001). Importantly, other interactions were found. When the target was in front (0°) and changed direction, the participant only turned (F(2,33)=1531.41, p< 0.001); but when the target was to the side (60°), the participant both turned (F(2,33)=2018.19, p< 0.001) and changed speed (F(2,33)=121.59, p< 0.001). Moreover, at 0° the response delay to speed change was shorter than to direction change, but this relation reversed at 30° and 60° (F(2,66)=45.1, p< 0.001). These results are consistent with optical expansion controlling speed and bearing controlling heading when the target is in front, but these reverse when the target is to the side. In Experiment 2, we independently manipulate the target's bearing and expansion. Preliminary results suggest that the effect of optical expansion depends on target position. These findings imply that an individual pedestrian's motion is driven by the visual information that couples them to their visible neighbors. Supported by NSF BCS-1431406
Meeting abstract presented at VSS 2016
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