Tangible user interfaces seek to make computing natural and ubiquitous by coupling digital information with physical objects. The thesis contributes to this field by presenting empirical research on tangible computing and touch interaction.

In the area of tangible computing, the thesis first presents mixiTUI, a tangible sequencer that allows electronic musicians to play their music live. mixiTUI was developed in collaboration with electronic musicians and aims to balance preparation and improvisation in staging live performances. mixiTUI was evaluated in a concert with 117 participants and the results suggest that mixiTUI improved both the audience’s and the musician’s experience.

To enhance the interaction with tangible user interfaces,we developed Tangible Bots, a set of active, motorized tangibles. Tangible Bots assist users by providing haptic feedback, by correcting interaction errors, by supporting multi-touch control, and by allowing efficient interaction with multiple tangibles. These benefits were evaluated in a study that shows that rotation-based interactions were more efficient with Tangible Bots. A second study demonstrated usefulness by observing how electronic musicians use Tangible Bots to create music with amodified version of mixiTUI.

To further investigate motion in tangible user interfaces, we reviewed 44 papers and surveyed the design space of shape-changing interfaces. In the review, we identified eight types of shape that are transformed in various ways to serve both functional and hedonic design purposes.

Three questions are discussed based on the review: (a) which design purposes may shape-changing interfaces be used for, (b) which parts of the design space are not well understood, and (c) why studying user experience with shape-changing interfaces is important.

In the area of touch interactions, we report on results from a study that investigated the influence of display orientation on users’ performance and satisfaction. Using a horizontal and a vertical touch screen, we studied 16 participants as they tapped, dragged, and interacted bimanually.

Results show that orientation impacted both performance and error rates. Tapping was performed 5% faster on the vertical surface, whereas dragging was performed 5% faster and with fewer errors on the horizontal surface. The vertical surface was perceived as more physically demanding to use than the horizontal surface.

Finally, the thesis investigates how touch interaction can become more expressive. We do this by presenting Expressive Touch, a tabletop interface that infers tapping force from the sound waves created by the users’ finger upon impact. Using Expressive Touch, we studied participants’ perception of tapping force and investigated their ability to control it. Results show that participants could produce two different force levels with 98% accuracy. For six levels of force, accuracy dropped to 58%.

Seven demo applications showcase the capabilities of Expressive Touch and are used to evaluate the usability and usefulness of force tapping.

Overall, the interaction techniques and technologies presented in the thesis show to enhance the interaction with tangible user interfaces and touch interfaces by making the interaction more expressive, efficient, and enjoyable.