Stereokinetic shapes and their shadows

The visual space of phenomenal appearances has a complex geometry which cannot be reduced strictly to Euclidean or projective geometry. The distinctive nature of this space and its objects is evidenced paradigmatically by stereokinetic phenomena, which are perceptual objects in actual three-dimensional coming into being. Stereokinetic phenomena produce the appearance not only of corporeality but also, in certain circumstances, of shadows. By altering certain components of his experiments on the three-dimensional appearance of a truncated cone, in fact, Musatti discovered that on its white base floats some sort of shadow obscuring stretches of the white lines. These shadows are connected to phenomena of amodal presentations successively analysed by Kanizsa. The continuity of the unfolding in visual space of stereokinetic transformations produces a diversified series of percepts coming into being, shadows included, and highlights the role of configurational movement as a factor of formal unification, thereby proposing once again the hypothesis of assimilative factors as responsible for the field organisation of past experience.