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.