This new double-sided multi-touch mobile interaction model enables intuitive finger gestures for manipulating 3D objects and user interfaces on a 2D screen. Although multi-touch input enables scrolling and the zooming of a document, its manipulation is constrained to two dimensions over the horizontal or vertical planes of a mobile device’s 2D touch screen. By adding touch inputs from the device’s back side, the degree of freedom for manipulation can be extended to a pseudo three dimensions.
Source: E.E. Shen, S.D. Tsai, H. Chu, Y.J. Hsu, and C.E. Chen, “Double-side multi-touch input for mobile devices,” Proceedings of the 27th international conference extended abstracts on Human factors in computing systems, Boston, MA, USA: ACM, 2009, pp. 4339-4344. (Poster in PDF format is available at NTU Ubicomp Laboratory)