We present Headbang, an interaction technique that enriches touch input on handheld devices through slight head movement gestures. This way, users can easily execute shortcuts, like Copy, Paste, or Share, to on-screen targets while touching them. Headbang utilizes the capabilities of commodity smartphones to track the user’s head with their front facing cameras. We evaluated Headbang in two studies and show that the system can be reliably used while sitting and walking and offers a similar accuracy and speed as touch interaction.

Tangibles on multitouch tabletops increase speed, accuracy, and eyes-free operability for individual users, and verbal and behavioral social interaction among multiple users around smaller tables with a shared focus of attention. Modern multitouch tables, however, provide sizes and resolutions that let groups work alongside each other in separate workspaces. But how aware do these users remain of each other's actions, and what impact can tangibles have on their awareness? In our study, groups of 2--4 users around the table played an individual game grabbing their attention as primary task, while they also had to occasionally become aware of other players'actions and react as secondary task. We found that players were significantly more aware of other players'actions using tangibles than those using pure multitouch interaction, indicated by faster reaction times. This effect was especially strong with more players. We close with qualitative user feedback and design recommendations. We found that players were significantly more aware of other players'actions using tangibles than those using pure multitouch interaction, indicated by faster reaction times. This effect was especially strong with more players. We close with qualitative user feedback and design recommendations.

Exploring source code history is an important task for software maintenance. Traditionally, source code history is navigated on the granularity of individual files. This is not fine-grained enough to support users in exploring the evolution of individual code elements. We suggest to consider the history of individual elements within the tree structure inherent to source code. A history graph created from these trees then enables new ways to explore events of interest defined by structural changes in the source code. We present Tree Flow, a visualization of these structural changes designed to enable users to choose the appropriate level of detail for the task at hand. In a user study, we show that both Chronicler and the history aware timeline, two prototype systems combining history graph navigation with a traditional source code view, outperform the more traditional history navigation on a file basis and users strongly prefer Chronicler for the exploration of source code.

Using a smartphone for touch input to control apps and games mirrored to a distant screen is difficult, as the user cannot see where she is touching while looking at the distant display. We present HaptiCase, an interaction technique that provides back-of-device tactile landmarks that the user senses with her fingers to estimate the location of her finger in relation to the touchscreen. By pinching the thumb resting above the touch- screen to a finger at the back, the finger position is transferred to the front as the thumb touches the screen. In a study, we compared touch performance of different landmark layouts with a regular landmark-free mobile device. Using a land- mark design of dots on a 3x5 grid significantly improves eyes-free tapping accuracy and allows targets to be as small as 17.5 mm---a 14% reduction in target size---to cover 99% of all touches. When users can look at the touchscreen, land- marks have no significant effect on performance. HaptiCase is low-cost, requires no electronics, and works with unmodified software.

Tangible objects on capacitive multi-touch surfaces are usually only detected while the user is touching them. When the user lets go of such a tangible, the system cannot distinguish whether the user just released the tangible, or picked it up and removed it from the surface. We introduce PERCs, persistent capacitive tangibles that "know" whether they are currently on a capacitive touch surface or not. This is achieved by adding a small field sensor to the tangible to detect the touch screen's own, weak electromagnetic touch detection probing signal. Thus, unlike previous designs, PERCs do not get filtered out over time by the adaptive signal filters of the touch screen. We provide a technical overview of the theory be- hind PERCs and our prototype construction, and we evaluate detection rates, timing performance, and positional and angular accuracy for PERCs on a variety of unmodified, commercially available multi-touch devices.Through their affordable circuitry and high accuracy, PERCs open up the potential for a variety of new applications that use tangibles on today's ubiquitous multi-touch devices.