The Role of Retinal Flow in Walking

Both visual direction and optic flow have been implicated in walking towards a goal, in experiments that use prisms to alter visual direction. However, prisms bias retinal flow patterns in ways that may affect balance. This will alter foot placement, and indirectly, a walkers path. We used a prism manipulation in virtual reality for goal-directed walking, where we manipulated the location of texture-defined flow as well as direction of gaze. The addition of texture straightened paths, but primarily when it provided flow on the ground plane. Texture only on the ground produced straightening comparable to full-scene texture, whereas wall-only texture produced little straightening. This reveals a disproportionate contribution of motion generated on the ground plane to control locomotion, potentially reflecting higher retinal speeds and the prism-induced rotations in the lower visual field. This suggests that, when visual direction is manipulated by a prism, trajectories might result from unexpected motion patterns that activate a balance response, leading to compensatory foot placement. Thus trajectories may be shaped by complex interactions between goal direction, gaze, and local retinal motion patterns.