Abstract : The autokinetic, oculogyral, and oculogravic illusions all involve apparent motion or displacement of the visual field with respect to an observer. It is shown that these illusions are related to involuntary eye movements, occurring either spontaneously as in the autokinetic illusion, or in response to the special stimuli associated with the other two illusions. During fixation the visual sensation of movement seems to be produced by, or related to, the pattern of efferent activity aimed at the group of extraocular muscles which will act as antagonists to the involuntary eye movement referred to.