The optokinetic nystagmus is a phylogenetically old reflexive reaction of the eyes to the movements of the visual surroundings. Two components can be distinguished: (1) the direct one is considered to represent a cortically transmitted loop through the posterior parietal areas: MT and MST; (2) the indirect component passes through brain stem nuclei. One of them is the pretectal nucleus of the optic tract in which we found neurons related to the velocity of the moving pattern. Since in neurons of the oculomotor nuclei the neuronal activity is related to eye position, integration must take place somewhere in the circuit. The brain stern-mediated indirect component is influenced by the vestibular organs, not only by semicircular canals but also by otoliths.