Fixation or
visual fixation is the maintaining of the
visual gaze on a single location. Humans (and other animals with a
fovea) typically alternate
saccades and visual fixations, the notable exception being in
smooth pursuit, controlled by a different neural substrate that appear to have developed for hunting prey. There are three categories of fixational eye movements:
microsaccades, ocular drifts, and
ocular microtremor. Fixational eye movement has been found in a number of species, including humans, other primates, cats, rabbits, turtles, salamanders, and owls. Although their existence has been known since the 1950s, the role and importance of fixational eye movement is still debated.