Relative contributions of optic flow, bearing, and splay angle information to lane keeping.

Heading from optic flow, bearing, and splay angle information can all be used for lane keeping on a straight path. Here we investigated the relative contributions of these three visual cues to accurate lane-keeping control in a novel way. The displays simulated observers steering a vehicle down a straight path defined by a pair of posts (providing bearing angles only) or a segment of lane edges (providing bearing and splay angles) at a fixed viewing distance, and the ground contained no flow, sparse flow, or dense flow. Observers used a joystick to control the vehicle's lateral movement to stay in the center of the lane while facing random perturbations to both the vehicle's lateral position and orientation. The lateral position perturbation affected the use of both splay and bearing angle cues, but the vehicle orientation perturbation only affected the use of bearing angles. We found that performance improved as more flow information was added to the scene regardless of the availability of bearing or splay angle information. In the presence of splay angles, observers would ignore bearing and rely mainly on splay angles for lane keeping.