Abstract
Outside of the lab, people usually move relative to other moving people. Moving and stationary people perceive human movement differently (Jacobs & Shiffrar, 2005). Here we examine the cues that walking observers use to compare their own gait speed to the gait speed of a nearby walker. Naive subjects walked on a treadmill set at various speeds ranging from 2 to 3 mph. On each trial, the gait of the projected walker was 0.3 mph faster or slower than the subject's own gait speed. Subjects reported whether they walked faster or slower than the projected walker. To determine whether body form influences the perception of relative gait speed, the projected walker was depicted as either a point-light walker or a fully embodied humanoid. Gait speed discrimination performance was superior with the embodied walker suggesting that body structure contributes to gait perception. Normally, faster walkers change their position relative to slower walkers. To determine whether perceived gait speed depends upon a perceived walker's position relative to a walking observer, the projected walker slowly translated forward or backward while walking. Gait speed discrimination was influenced by walker position at large but not small position changes. Finally, gait speed discriminations with near and far walkers were compared. Performance was best with near walkers. Taken together, these results suggest that body form and location contribute to the visual analysis of human gait by walking observers.