Void shadows: multi-touch interaction with stereoscopic objects on the tabletop

In this paper we present the Void Shadows interaction - a novel stereoscopic 3D interaction paradigm in which each virtual object casts a shadow on a touch-enabled display surface. The user can conveniently interact with such a shadow, and her actions are transferred to the associated object. Since all interactive tasks are carried out on the zero-parallax plane, there are no accommodation-convergence or related 2D/3D interaction problems, while the user is still able to "directly" manipulate objects at different 3D positions, without first having to position a cursor and to select an object. In an initial user study we have proved the applicability of the metaphor for some common tasks, and we have found that compared to in-air 3D interaction techniques the users performed up to 28% more precisely using about the same amount of time.