Patrick Baudisch - Back-of-Device Interaction Allows Creating Very Small Touch Devices

In this talk, I will discuss how to add pointing input capabilities to very small screen devices. On first sight, touchscreens seem to allow for particular compactness, because they integrate input and screen into the same physical space. The opposite is true, however, because the user’s fingers occlude contents and prevent precision. I argue that the key to touch-enabling very small devices is to use touch on the device backside. In order to study this, we have created a 2.4” prototype device; we simulate screens smaller than that by masking the screen. I present a user study in which participants completed a pointing task successfully across display sizes when using a back-of device interface. The touchscreen-based control condition (enhanced with the shift technique), in contrast, failed for screen diagonals below 1 inch. I present four form factor concepts based on back-of-device interaction and provide design guidelines extracted from a second user study.