Human beings generally find their way through environments with ease and without injury. During a normal walk, a pedestrian must judge direction of movement with an accuracy of about 4 degrees of visual angle (about the width of two thumbs held at arms' length). Otherwise he or she risks injury; a driver or pilot risks worse, and must attain considerably greater accuracy. Previously it has been shown that people can find their way based on information in the global pattern of movement at the back of the eye, called the retinal flow. More particularly, as one moves through the environment, an individual's natural mode of looking entails a cycle of pursuit fixations and saccades. That is, an observer looks at a given object (say to the left of his or her path) while moving forward on a linear or curvilinear path. The pursuit fixation entails a smooth counterclockwise eye rotation during locomotion. He or she then saccades rightward to a new object, entailing an abrupt clockwise eye movement. This cycle generally repeats, either again on the left side or reversing to the right. Several sources of information are available in the retinal flow during pursuit fixation. The two most important are differential motion parallax (DMP), the relative motion around a fixated object where near objects move faster than, and in the opposite direction from, far objects, and inward motion (IM), the motion of objects toward the fovea. These studies will continue this basic line of research, investigating further the utility of DMP and IM, and exploring new sources of information, including several entailed in a constant gaze-movement angle which may be useful in detecting collisions. In particular, the experiments will determine how moving observers negotiate moving objects in a rigid environment. The research should result in a deeper theoretical understanding of the limits and nature of human beings' wayfinding ability, with a long-term aim of promoting traffic safety. Stimuli will be presented to individual viewers on a computer screen and will be manipulated in ways that obey the mechanics of the real world and the biomechanics of human locomotion.
