The autokinetic effect (also referred to as autokinesis) is a phenomenon of visual perception in which a stationary, small point of light in an otherwise dark or featureless environment appears to move. It was first recorded by a Russian officer keeping watch who observed illusory movement of a star near the horizon. It presumably occurs because motion perception was always relative to some reference point. In darkness or in a featureless environment there is no reference point, so the movement of the single point is undefined. The direction of the movements does not appear to be correlated with the involuntary eye movements, but may be determined by errors between eye position and that specified by efference copy of the movement signals sent to the extraocular muscles.
The amplitude of the movements is also undefined. Individual observers set their own frames of reference to judge amplitude (and possibly direction). Because the phenomenon is labile, it has been used to show the effects of social influence or suggestion on judgements. For example, if an observer who would otherwise say the light is moving one foot overhears another observer say the light is moving one yard then the first observer will report that the light moved one yard. Discovery of the influence of suggestion on the autokinetic effect is often attributed to Sherif (1935), but it was recorded by Adams (1912), if not others.
Alexander von Humboldt observed the phenomenon in 1799 while looking at stars with the naked eye, but thought it was a real movement of the stars. Thus he named them "Sternschwanken" i.e. "Swinging Stars". It was not until 1857 that G. Schweitzer (Schweitzer, 1857), an early German psychologist, discovered that is was a subjective phenomenon. The US Navy started studying this in 1945 in order to explain vertigo experiences related by pilots. Today this "kinetic illusion" is categorized as a vestibular-induced illusion, see vestibular system.
Many sightings of UFOs have also been attributed to the autokinetic effect's action on looking at stars or planets.