It has been argued that transparent displays are beneficial for certain tasks by allowing users to simultaneously see on-screen content as well as the environment behind the display. However, it is yet unclear how much in background awareness users gain and if performance suffers for tasks performed on the transparent display, since users are no longer shielded from distractions. Therefore, we investigate the influence of display transparency on task performance and background awareness in a dual-task scenario. We conducted an experiment comparing transparent displays with conventional displays in different horizontal and vertical configurations. Participants performed an attention-demanding primary task on the display while simultaneously observing the background for target stimuli. Our results show that transparent and horizontal displays increase the ability of participants to observe the background while keeping primary task performance constant.

We present a quantitative and qualitative analysis of interruptions of interaction with a public display game, and explore the use of a manual pause mode in this scenario. In previous public display installations we observed users frequently interrupting their interaction. To explore ways of supporting such behavior, we implemented a gesture controlled multiuser game with four pausing techniques. We evaluated them in a field study analyzing 704 users and found that our pausing techniques were eagerly explored, but rarely used with the intention to pause the game. Our study shows that interactions with public displays are considerably intermissive, and that users mostly interrupt interaction to socialize and mainly approach public displays in groups. We conclude that, as a typical characteristic of public display interaction, interruptions deserve consideration. However, manual pause modes are not well suited for games on public displays. Instead, interruptions should be implicitly supported by the application design.

While whole body interaction can enrich user experience on public displays, it remains unclear how common visualizations of user representations impact users' ability to perceive content on the display. In this work we use a head-mounted eye tracker to record visual behavior of 25 users interacting with a public display game that uses a silhouette user representation, mirroring the users' movements. Results from visual attention analysis as well as post-hoc recall and recognition tasks on display contents reveal that visual attention is mostly on users' silhouette while peripheral screen elements remain largely unattended. In our experiment, content attached to the user representation attracted significantly more attention than other screen contents, while content placed at the top and bottom of the screen attracted significantly less. Screen contents attached to the user representation were also significantly better remembered than those at the top and bottom of the screen.

We present GelTouch, a gel-based layer that can selectively transition between soft and stiff to provide tactile multi-touch feedback. It is flexible, transparent when not activated, and contains no mechanical, electromagnetic, or hydraulic components, resulting in a compact form factor (a 2mm thin touchscreen layer for our prototype). The activated areas can be morphed freely and continuously, without being limited to fixed, predefined shapes. GelTouch consists of a poly(N-isopropylacrylamide) gel layer which alters its viscoelasticity when activated by applying heat (>32 C). We present three different activation techniques: 1) Indium Tin Oxide (ITO) as a heating element that enables tactile feedback through individually addressable taxels; 2) predefined tactile areas of engraved ITO, that can be layered and combined; 3) complex arrangements of resistance wire that create thin tactile edges. We present a tablet with 6x4 tactile areas, enabling a tactile numpad, slider, and thumbstick. We show that the gel is up to 25 times stiffer when activated and that users detect tactile features reliably (94.8%).

We present the design and evaluation of MyPosition, a public display in the form of a large projection, featuring an interactive poll visualization. MyPosition aims at facilitating the deliberation and comparison of individual opinions on locally relevant topics in an opportunistic and engaging way. We evaluated MyPosition in an in-the-wild study and demonstrated that the engaging nature of the installation was effective in enticing public discussion. We found that (i) the increased identifiability of users positively impacted the engagement with and the social debate around the installation, however lowered the actual polling rate; (ii) people submitted their personal opinion instead of playing around with the interactive features; and (iii) the display led to considerable discussion as well as nudging among people, in particular in zones beyond the interaction area in front of the screen.

Most of today's public displays only show predefined contents that passers-by are not able to change. We argue that interactive public displays would benefit from immediately usable mid-air techniques for choosing options, expressing opinions or more generally selecting one among several items. We propose a design space for hand-gesture based mid-air selection techniques on interactive public displays, along with four specific techniques that we evaluated at three different locations in the the field. Our findings include: 1) if no hint is provided, people successfully use Point+Dwell for selecting items, 2) the user representation could be switched from Mirror to Cursor after registration without causing confusion, 3) people tend to explore items before confirming one, 4) in a public context, people frequently interact inadvertently (without looking at the screen). We conclude by providing recommendations for designers of interactive public displays to support immediate usability for mid-air selection.

We present Tracs, a dual-sided see-through display system with controllable transparency. Traditional displays are a constant visual and communication barrier, hindering fast and efficient collaboration of spatially close or facing co-workers. Transparent displays could potentially remove these barriers, but introduce new issues of personal privacy, screen content privacy and visual interference. We therefore propose a solution with controllable transparency to overcome these problems. Tracs consists of two see-through displays, with a transparency-control layer, a backlight layer and a polarization adjustment layer in-between. The transparency-control layer is built as a grid of individually addressable transparency-controlled patches, allowing users to control the transparency overall or just locally. Additionally, the locally switchable backlight layer improves the contrast of LCD screen content. Tracs allows users to switch between personal and collaborative work fast and easily and gives them full control of transparent regions on their display.

We investigate how to reveal an initial mid-air gesture on interactive public displays. This initial gesture can serve as gesture registration for advanced operations. We propose three strategies to reveal the initial gesture: spatial division, temporal division and integration. Spatial division permanently shows the gesture on a dedicated screen area. Temporal division interrupts the application to reveal the gesture. Integration embeds gesture hints directly in the application. We also propose a novel initial gesture called Teapot to illustrate our strategies. We report on a laboratory and field study. Our main findings are: A large percentage of all users execute the gesture, especially with spatial division (56%). Users intuitively discover a gesture vocabulary by exploring variations of the Teapot gesture by themselves, as well as by imitating and extending other users' variations.

Most interactive public displays currently rely on flat screens. This form factor impacts how users (1) notice the public display (2) develop motivation and (3) (socially) interact with the public display. In this paper, we present Chained Displays, a combination of several screens to create different form factors for interactive public displays. We also present a design space based on two complementary concepts, Focus and Nimbus, to describe and compare chained display configurations. Finally, we performed a field study comparing three chained displays: Flat, Concave, and Hexagonal. Results show that Flat triggers the strongest honeypot effect, Hexagonal causes low social learning, and Concave triggers the smallest amount of simultaneously interacting users among other findings.

In this paper we present our findings from a lab and a field study investigating how passers-by notice the interactivity of public displays. We designed an interactive installation that uses visual feedback to the incidental movements of passers-by to communicate its interactivity. The lab study reveals: (1) Mirrored user silhouettes and images are more effective than avatar-like representations. (2) It takes time to notice the interactivity (approx. 1.2s). In the field study, three displays were installed during three weeks in shop windows, and data about 502 interaction sessions were collected. Our observations show: (1) Significantly more passers-by interact when immediately showing the mirrored user image (+90%) or silhouette (+47%) compared to a traditional attract sequence with call-to-action. (2) Passers-by often notice interactivity late and have to walk back to interact (the landing effect). (3) If somebody is already interacting, others begin interaction behind the ones already interacting, forming multiple rows (the honeypot effect). Our findings can be used to design public display applications and shop windows that more effectively communicate interactivity to passers-by.

We propose a course design that fits a practical game development project into a regular game design lecture course. As this approach requires a consistent structure, our concept proposes an adaption of Scrum that is based on the game development life-cycle: ABC-Sprints consist of three Sprints to iteratively create Alpha, Beta and Completed versions of a game. We present a detailed walkthrough of the course and give results of a formal evaluation. These indicate that ABC-Sprints help students to manage their workload and to increase productivity over time. Consequently, three teams each presented a game at the end of the course that technically exceeded typical outcomes of game projects without lectures. We hence encourage to apply ABC-Sprints to other curricula and provide a set of recommendations.