Modeling observer and object motion perception

When a person moves about the world, images of the surrounding scene move across his or her retinas, providing a rich source of information about the environment. The motion of the images arises from numerous sources. The observer’s own locomotion causes the images of all stationary items to move in a pattern. This pattern of image velocities on the retina is known as optic flow or retinal flow. This pattern can be a fairly simple, radial pattern (Figure 1a) if the observer moves in a straight line, or more complex (Figure 1b) if the observer moves on a curved path. In addition, the observer may make eye or head movements that also affect the flow field. Finally, objects in the world may themselves be moving, creating additional complexity in the scene (Figure 1c). Somehow the brain is able to process this motion information adeptly to ascertain the direction of motion of the observer as well as the position and direction of motion of moving objects in the scene. This ability allows soccer players to follow a moving ball while maneuvering past other running players, and drivers on busy roads to avoid moving cars and pedestrians while driving straight or negotiating turns.