The two-thirds power law in motion perception

Abstract

If a visual motion abruptly vanishes, the vanishing point is mislocalized in the anticipated direction of the motion (cf. Freyd Finke, 1984; Hubbard Bharucha, 1988; Verfaillie & d'Ydewalle, 1991). Here, we replicate this effect for curvilinear motions, showing that the compatibility with human movements, as expressed by the two-thirds power law (cf. Lacquaniti, Terzuolo, Viviani, 1983; Viviani, 2002), specifically contribute to this anticipation error. Thus, the compatibility effect does not manifest itself solely in an overshooting of the judged vanishing position in comparison to the objective vanishing position, but also in a more accurate anticipation of the curvilinearity of the forthcoming motion. The latter effect only occurred for spatially unpredictable target motions. Spatially more predictable target motions allowed for a different kind of anticipation, which overrode the compatibility effect. The results are discussed with regard to the notion of an action-related influence on motion perception.