Can where we are tell us where to go? The role of positional cues in visual guidance of human walking

Warren et al.(2001) investigated the role of optic flow and egocentric direction in the visual guidance of walking. They dissociated perceived and walking direction and measured walking trajectories in four different scenes that ranged in complexity from a single target line to a textured room containing posts. Trajectories became progressively straighter, and so less compatible with the use of egocentric direction, as the scenes became more complex. They interpreted the change in trajectory as due to the increasing availability of optic flow. However, the complex scenes also introduced geometric cues, positional cues, and motion parallax. We sought to tease the contribution of these cues out. Using a VR system we first replicated two scenes in Warren et al.’s study, the single line scene and the room plus posts scene. Our data closely replicated their results, we found that trajectories were markedly straighter in the room condition. We then isolated optic flow so that we could evaluate its contribution. We used a single target line scene as before, an empty room, and an isolated cloud of dots that filled the volume of the room. The dot scene provides the same amount of optic flow as the room plus posts scene that was used previously. Therefore if the change in trajectories is due to an increased amount of optic flow then trajectories in the dot scene should be at least as straight as in the empty room scene. What we found was that the trajectories in the dot condition were more curved than in the empty room condition and similar to those obtained in the single line environment. These results suggest that geometric or positional cues play a previously unrecognised role in the visual guidance of walking