User studies and expert reviews are established methods for evaluating usability and user experience (UX) in user-centered design. However, practitioners often struggle to integrate these often time-consuming and costly methods in their design processes. As technological products and services are becoming increasingly mobile, their contexts of use are increasingly diverse and less predictable. While this changing context is hard to capture in lab studies, the same mobile technologies also provide possibilities for new study methods. In this paper we advocate lightweight mobile tools for crowdsourcing UX feedback. In cooperation with a design agency, we built two apps that allow users to express feedback with text, ratings and pictures whenever using a product. The second app assigns feedback to categories, while the first does not. In a case study we compared the quantity, relevance, and nature of the feedback collected with both UX evaluation apps to traditional evaluation methods. The feedback collected with the apps was considered highly useful by designers and provided more user stories and context than traditional evaluations.

We address novel two-handed interaction techniques in dual display interactive workspaces combining direct and indirect touch input. In particular, we introduce the notion of a horizontal tool space with task-dependent graphical input areas. These input areas are designed as single purpose control elements for specific functions and allow users to manipulate objects displayed on a vertical screen using simple one- and two-finger touch gestures and both hands. For demonstrating this concept, we use 3D modeling tasks as a specific application area. Initial feedback of six expert users indicates that our techniques are easy to use and stimulate exploration rather than precise modeling. Further, we gathered qualitative feedback during a multi-session observational study with five novices who learned to use our tool and were interviewed several times. Preliminary results indicate that working with our setup is easy to learn and remember. Participants liked the partitioning character of the dual-surface setup and agreed on the benefiting quality of touch input, giving them a 'hands-on feeling'.

Drivers attend to a lot of information at various locations inside and outside the car as well as on external devices (e.g. smart phones). Head-Up Displays (HUDs) support keeping drivers' visual focus directed towards the street; as they present virtual information in the windshield area on top of the physical world within the field of view of the driver. Displayed information, however, is often spatially dissociated with its cause in the physical world: for example a warning is displayed, yet drivers still require time searching for the hazard causing it. Windshield displays (WSDs) allow virtual warnings being displayed at the position of the hazard. We compared HUD and WSD with the baseline no-display and found that drivers demonstrate a calm gaze behavior with WSDs; they keep their visual attention in average 1.5 s longer focused on the leading car. However, we also found no significant faster reaction time compared to HUDs. We discuss our findings comparing HUDs to WSDs, present potential limitations of our study and point out future steps in order to further investigate the advantages of WSDs.

Mid-air gestures are initial hand poses with a subsequent movement. Existing gesture guides reveal this dynamic part of a gesture. Initial poses, however, are either revealed by space-consuming cheat sheets or time-consuming demonstration videos. Mime is a novel interaction concept that (1) reveals how to form complex hand poses and (2) teaches pose-command mappings: Mime reduces hand poses to space-efficient line figures that users mime with their hands; these abstract lines are embedded into command icons or names to create a mnemonic. We present several applications of the Mime concept, and implemented a prototype based on mid-air back-of-device interaction on off-the-shelf mobile phones. We compared both mnemonics, iconic and textual, to a baseline without embedding to test learnability and memorability of a 12-item vocabulary. Users in the iconic condition required significantly less training than both other conditions and recalled significantly more items after one week compared to the no-cue baseline.

Despite the demonstrated benefits of multi-finger input, todays gesture vocabularies offer a limited number of postures and gestures. Previous research designed several posture sets, but does not address the limited human capacity of retaining them. We present a multi-finger chord vocabulary, introduce a novel hand-centric approach to detect the identity of fingers on off-the-shelf hand-held tablets, and report on the detection accuracy. A between-subjects experiment comparing "random" to a "categorized" chord-command mapping found that users retained categorized mappings more accurately over one week than random ones. In response to the logical posture-language structure, people adapted to logical memorization strategies, such as 'exclusion', 'order', and 'category', to minimize the amount of information to retain. We conclude that structured chord-command mappings support learning, short-, and long-term retention of chord- command mappings.

We introduce BodyScape, a body-centric design space that allows us to describe, classify and systematically compare multi-surface interaction techniques, both individually and in combination. BodyScape reflects the relationship between users and their environment, specifically how different body parts enhance or restrict movement within particular interaction techniques and can be used to analyze existing techniques or suggest new ones. We illustrate the use of BodyScape by comparing two free-hand techniques, on-body touch and mid-air pointing, first separately, then combined. We found that touching the torso is faster than touching the lower legs, since it affects the user's balance; and touching targets on the dominant arm is slower than targets on the torso because the user must compensate for the applied force.

Despite the demonstrated benefits of bimanual interaction, most tablets use just one hand for interaction, to free the other for support. In a preliminary study, we identified five holds that permit simultaneous support and interaction, and noted that users frequently change position to combat fatigue. We then designed the BiTouch design space, which introduces a support function in the kinematic chain model for interacting with hand-held tablets, and developed BiPad, a toolkit for creating bimanual tablet interaction with the thumb or the fingers of the supporting hand. We ran a controlled experiment to explore how tablet orientation and hand position affect three novel techniques: bimanual taps, gestures and chords. Bimanual taps outperformed our one-handed control condition in both landscape and portrait orientations; bimanual chords and gestures in portrait mode only; and thumbs outperformed fingers, but were more tiring and less stable. Together, BiTouch and BiPad offer new opportunities for designing bimanual interaction on hand-held tablets.

Very-high-resolution wall-sized displays offer new opportunities for interacting with large data sets. While pointing on this type of display has been studied extensively, higher-level, more complex tasks such as pan-zoom navigation have received little attention. It thus remains unclear which techniques are best suited to perform multiscale navigation in these environments. Building upon empirical data gathered from studies of pan-and-zoom on desktop computers and studies of remote pointing, we identified three key factors for the design of mid-air pan-and-zoom techniques: uni- vs. bimanual interaction, linear vs. circular movements, and level of guidance to accomplish the gestures in mid-air. After an extensive phase of iterative design and pilot testing, we ran a controlled experiment aimed at better understanding the influence of these factors on task performance. Significant effects were obtained for all three factors: bimanual interaction, linear gestures and a high level of guidance resulted in significantly improved performance. Moreover, the interaction effects among some of the dimensions suggest possible combinations for more complex, real-world tasks.

This paper explores the need for sustainable design with paper: how people really print and how we can take advantage of novel, reusable paper technology. We conducted two studies to investigate user's printing behavior. A key finding of the first study was that users often need an intermediate state between the electronic and physical forms of their documents. The second study examined users' predictions of which types of documents required this intermediate state. We formulate these findings into design guidelines that take into account: examination phase, transitions, cognitive and emotional reasons, and task- and event-relevant documents. Finally, we discuss how the different physical characteristics of reusable paper affect the user interface and could effectively support sustainable design.

We present Silicone iLluminated Active Peripherals (SLAP), a system of tangible, translucent widgets for use on multitouch tabletops. SLAP Widgets are cast from silicone or made of acrylic, and include sliders, knobs, keyboards, and buttons. They add tactile feedback to multi-touch tables, improving input accuracy. Using rear projection, SLAP Widgets can be relabeled dynamically, providing inexpensive, battery-free, and untethered augmentations. Furthermore, SLAP combines the flexibility of virtual objects with physical affordances. We evaluate how SLAP Widgets influence the user experience on tabletops compared to virtual controls. Empirical studies show that SLAPWidgets are easy to use and outperform virtual controls significantly in terms of accuracy and overall interaction time.

We present SLAPbook, an application using SLAP, translucent and tangible widgets for use on vision-based multi-touch tabletops in Single Display Groupware (SDG) environments. SLAP stands for Silicone ILluminated Active Peripherals and includes widgets such as sliders, knobs, keyboards, and buttons. The widgets and tactile feedback to multi-touch tables while simultaneously providing dynamic relabeling to tangible objects using the table's rear projection. SLAPbook provides multiple users the ability to add and edit content to a guestbook, browse other peoples' entries, and access personal data using a token-based personalization system. Interaction with the table takes place in the personal and public space so that users can make use of personal and shared controls to perform separate and coordinative actions.