Where we look determines what we see. Because human vision varies greatly with retinotopic location, with high spatial resolution limited to the fovea, humans have evolved a sophisticated ocular motor system, much of it aimed at stabilizing vision on objects of interest, despite the fact that we are mobile creatures and live in dynamic environments. Thus fixation serves to hold our gaze on a stationary object, while the vestibular and optokinetic systems work together to stabilize that gaze while our bodies or heads are in motion. If the object is moving, the smooth pursuit system will use information about the object's trajectory to keep gaze on the object. Any failure of these systems to keep gaze directed at the object will create a position error signal that will trigger a corrective saccade. Finally saccades also have the function of shifting gaze to new objects of interest, following which all the systems mentioned will act to stabilize gaze on the new object.
Spencer S. Eccles Health Sciences Library, University of Utah